3D printing flaxseed gum fish-source protein gel adaptive to elderly swallowing and bionic digestion response as well as preparation method and application of 3D printing flaxseed gum fish-source protein gel

Abstract

The invention relates to the technical field of food processing, in particular to 3D printing flaxseed gum fish-source protein gel adaptive to elderly swallowing and bionic digestion response as well as a preparation method and application of the 3D printing flaxseed gum fish-source protein gel. According to the present invention, by constructing the lycopene-loaded flaxseed gum-myofibrillar protein composite gel system, the multi-scale structure regulation and the lycopene precise delivery are achieved, and the function adaptation mechanism of the lycopene in the 3D printing swallowing food is systematically clarified; the invention focuses on a molecular mechanism that flaxseed gum molecule acting force rearrangement drives myofibrillar protein secondary structure transformation, and combines rheological recovery characteristics of LFG gel under a dynamic shearing condition and a cross-scale regulation effect of swallowing kinetics, and further discloses a lycopene release behavior of the LFG gel in a process of simulating dynamic digestion of old people. From the synergetic perspective of molecular interaction, rheological response and digestive behavior regulation, reference is provided for the development of elderly special dietary food with swallowing suitability, accurate nutrition delivery and sensory palatability.

Description

Technical Field

[0001] The present invention relates to the field of food processing technology, and in particular to a 3D printed flaxseed glue fish-derived protein gel adapted to elderly swallowing and bionic digestive responses, as well as a preparation method and application thereof. Background Art

[0002] Traditional dysphagia foods utilize texture modification methods such as thickening and crushing to ensure swallowing safety, but these methods suffer from drawbacks such as loss of nutrient density, inefficient delivery of functional factors, and a monotonous taste. In recent years, 3D printing technology has provided a new path for the development of personalized dysphagia foods. By precisely controlling the rheological properties and morphological adaptability of materials, customized soft foods can meet the needs of individuals with different dysphagia groups. However, starch or single-protein gels suffer from bottlenecks such as insufficient mechanical strength and a limited nutrient carrier function, making it difficult to simultaneously meet the requirements for swallowing safety and functional nutrient delivery. While polysaccharides such as carrageenan and konjac glucomannan can enhance the water-holding capacity of myofibrillar protein gels, excessive use can cause viscoelastic imbalances, leading to the risk of food bolus adhesion during pharyngeal passage. Flaxseed gum, as a soluble dietary fiber, has health benefits such as anti-diabetes, anti-hypertension, cholesterol-lowering, and colorectal cancer prevention. Prior art suggests that flaxseed gum is a potential thickener for dysphagia patients, exhibiting excellent rheological and lubricating properties in various fluid matrices and enhancing the pleasure experienced during the final swallowing phase. However, the multi-scale structural (molecular-mesoscopic-macroscopic) regulation mechanism of flaxseed gum-myofibrillar protein gel is still unclear. In particular, how polysaccharide-protein interactions affect the release kinetics of active ingredients through molecular rearrangement under dynamic digestion conditions urgently needs to be systematically studied.

[0003] Lycopene, a potent fat-soluble antioxidant, has limited bioavailability due to its chemical instability and low water solubility. Furthermore, the gastrointestinal physiology of the elderly (such as decreased gastric acid secretion and delayed gastric emptying) can significantly alter the digestive behavior of carrier materials. Therefore, it is crucial to develop a lycopene-loaded protein gel suitable for swallowing by the elderly. Summary of the Invention

[0004] The present invention aims to provide a 3D-printed flaxseed gum and fish-derived protein gel that is adapted to the swallowing and biomimetic digestive responses of the elderly, as well as its preparation method and application, to address the aforementioned problems of the prior art. The present invention provides a 3D-printed flaxseed gum and fish-derived protein gel that is adapted to the swallowing and biomimetic digestive responses of the elderly. This 3D-printed flaxseed gum and fish-derived protein gel can be used to prepare 3D-printed food. This invention provides a reference for the development of specialized foods for the elderly that combine swallowing adaptability, precise nutrient delivery, and sensory palatability.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides a method for preparing a 3D printed flaxseed glue fish-derived protein gel adapted to elderly swallowing and biomimetic digestive responses, comprising the following steps:

[0007] Using ovate pomfret as a raw material to prepare fish-derived myofibrillar protein, and uniformly mixing the fish-derived myofibrillar protein with a buffer solution to obtain a fish-derived myofibrillar protein solution;

[0008] Evenly mixing lycopene and sunflower oil to obtain a lycopene solution;

[0009] Evenly mixing the fish-derived myofibrillar protein solution and flaxseed gum to obtain a flaxseed gum-fish-derived protein gel;

[0010] The lycopene solution and the flaxseed gum-fish source protein gel are evenly mixed to obtain the 3D printed flaxseed gum-fish source protein gel.

[0011] Preferably, the concentration of lycopene in the lycopene solution is 1 mg / g.

[0012] Preferably, the final concentration of the flaxseed gum in the 3D printed flaxseed gum fish-derived protein gel is 1.5-4wt%, the final concentration of the lycopene solution is 10wt%, and the final concentration of the fish-derived myofibrillar protein is 20wt%.

[0013] Further preferably, the final concentration of the flaxseed gum in the 3D printed flaxseed gum fish-derived protein gel is 3.5 wt %.

[0014] Preferably, the buffer solution is a 0.1 M NaCl solution.

[0015] Preferably, the method for preparing fish-derived myofibrillar protein comprises the steps of sequentially grinding and centrifuging the oval pomfret meat.

[0016] Preferably, the method for preparing fish-derived myofibrillar protein specifically comprises the following steps:

[0017] The oval pomfret meat is minced in an ice bath, and then centrifuged three times in a low phosphate buffer solution. The resulting precipitate is then centrifuged three times in a high phosphate buffer solution. The resulting supernatant is stored in a 4°C refrigerator for 2 hours and then centrifuged again. The resulting supernatant is mixed with distilled water and precipitated, and then centrifuged twice more to collect the precipitate to obtain the fish-derived myofibrillar protein.

[0018] Preferably, the low phosphate buffer comprises 0.005 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O and 15.5 mmol / L Na2HPO4·12H2O;

[0019] The high phosphate buffer comprises 0.6 mol / L NaCl, 3.38 mmol / L NaH2PO·2H2O and 15.5 mmol / L Na2HPO4·12H2O.

[0020] The present invention provides a 3D printed flaxseed glue fish-derived protein gel obtained by the above-mentioned preparation method.

[0021] The present invention provides the use of the above-mentioned 3D printed flaxseed glue fish-derived protein gel in the preparation of 3D printed food.

[0022] The present invention provides the use of flaxseed gum-fish protein gel in improving the embedding efficiency and / or bioaccessibility of lycopene. The preparation method of the flaxseed gum-fish protein gel comprises the following steps:

[0023] Using ovate pomfret as a raw material to prepare fish-derived myofibrillar protein, and uniformly mixing the fish-derived myofibrillar protein with a buffer solution to obtain a fish-derived myofibrillar protein solution;

[0024] The fish-derived myofibrillar protein solution and flaxseed gum are evenly mixed to obtain the flaxseed gum-fish-derived protein gel.

[0025] Further preferably, the method for preparing fish-derived myofibrillar protein comprises the steps of sequentially grinding and centrifuging the oval pomfret meat.

[0026] Further preferably, the method for preparing the fish-derived myofibrillar protein specifically comprises the following steps:

[0027] The oval pomfret meat is minced in an ice bath, and then centrifuged three times in a low phosphate buffer solution. The resulting precipitate is then centrifuged three times in a high phosphate buffer solution. The resulting supernatant is stored in a 4°C refrigerator for 2 hours and then centrifuged again. The resulting supernatant is mixed with distilled water and precipitated, and then centrifuged twice more to collect the precipitate to obtain the fish-derived myofibrillar protein.

[0028] Further preferably, the low phosphate buffer comprises 0.005 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O and 15.5 mmol / L Na2HPO4·12H2O;

[0029] The high phosphate buffer comprises 0.6 mol / L NaCl, 3.38 mmol / L NaH2PO·2H2O and 15.5 mmol / L Na2HPO4·12H2O.

[0030] The present invention discloses the following technical effects:

[0031] The present invention is dedicated to developing functional 3D printed foods suitable for elderly people with swallowing disorders. By constructing a lycopene-loaded flaxseed gum-myofibrillar protein composite gel system (LFG gel, i.e., 3D printed flaxseed gum fish protein gel), multi-scale structural regulation and precise delivery of lycopene are achieved, while systematically elucidating its functional adaptation mechanism in 3D printed swallowable foods. The present invention focuses on the molecular mechanism of the rearrangement of flaxseed gum molecular forces driving the transformation of the secondary structure of myofibrillar protein, and combines the rheological recovery characteristics of LFG gel under dynamic shear conditions and the cross-scale regulatory effect of swallowing dynamics to further reveal its lycopene release behavior in simulating the dynamic digestion process of the elderly. From the synergistic perspective of molecular interactions, rheological responses, and digestive behavior regulation, it provides a reference for the development of special dietary foods for the elderly that have both swallowing adaptability, precise nutrient delivery, and sensory palatability.

[0032] In the 3D-printed flaxseed gum fish-derived protein gel provided by the present invention, when the flaxseed gum addition amount is between 1.5wt% and 4wt%, especially at 3.5wt%, the flaxseed gum induces an alpha-helix rise through electrostatic shielding. The flaxseed gum promotes the formation of a dense elastic network, which can increase the lycopene encapsulation efficiency to 85.99%. In addition, the flaxseed gum optimizes the viscoelastic properties of the gel system through the entanglement of molecular chains, giving the gel good deformability and self-supporting strength. This not only ensures the smooth passage of the gel during swallowing, but also enables it to exhibit excellent recovery properties after experiencing high-speed shear. The present invention uses a biomimetic dynamic digestive system (DHSI-IV) to simulate the gastrointestinal environment of the elderly and found that the gel network undergoes conformational contraction in the gastric acid environment, delaying the release of lycopene. During the dynamic gastrointestinal digestion process, the release rate of lycopene from the 3D-printed flaxseed gum fish-derived protein gel is improved, the oil droplets in the digestate are more evenly distributed, and the micellization process of lycopene is significantly promoted, with its bioaccessibility reaching as high as 87.39%. According to the International Dysphagia Dietary Standards Initiative (IDDSI) standards, LEF-3.5% gel is classified as a Level 5 dysphagia food. This gel not only exhibits excellent 3D printing performance but is also highly compatible with the digestive characteristics of the elderly. This invention not only provides a theoretical basis for swallowing-safe 3D-printed foods but also offers a new approach to the coordinated regulation of "structure-function-digestive response" for addressing precise nutrition needs and the design of functional foods for the elderly. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 Surface hydrophobicity (a), FT-IR spectra (b) and Gaussian distribution fitting curves (ci) of gel systems with different formulations;

[0035] Figure 2 Results of G'(a), G"(b) and tanδ(c) of strain sweep, G'(d), G"(e) and tanδ(f) of frequency sweep, apparent viscosity (g), creep-recovery curve (h), 3ITT recovery curve (i) and microstructure of FG gel sample (j);

[0036] Figure 3 Lycopene encapsulation efficiency (a), interaction force (b), T2 relaxation time distribution curve (c), and MRI of LFG-0%-LFG-4% (di);

[0037] Figure 4 Strain sweeps (a), elastic Lissajous curves (b), and viscous Lissajous curves (c) of the sample at strain amplitudes of 1%, 10%, 100%, and 500%.

[0038] Figure 5 Frequency scan (a), apparent viscosity (b), creep-recovery curve (c), 3ITT recovery curve (d), and microstructure (e) results of LFG gel samples;

[0039] Figure 6 IDDSI test (a) and appearance of 3D printed gel (b);

[0040] Figure 7 The pH curve (a), gastric emptying curve (b), gastric digesta image (c), and microstructure (d) of the sample during dynamic gastric digestion in the DHSI-IV system;

[0041] Figure 8 Figure 1 shows the DIVHS system (a), the release rate of lycopene during in vitro dynamic gastric (b) and gastrointestinal (c) digestion in the DHSI-IV system, the bioavailability of lycopene (d), and the microstructure of the samples during in vitro dynamic gastrointestinal digestion (e).

[0042] Figure 9 The gellan gum-myofibrillar protein gel will undergo delamination during the heat induction process;

[0043] Figure 10 The stratification of acacia gum-myofibrillar protein gel occurs during heat induction.

[0044] Figure 11 This is the result of the spoon tilt test experiment;

[0045] Figure 12 This is the result of the investigation on the encapsulation efficiency of lycopene. DETAILED DESCRIPTION

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0047] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0048] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0049] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0050] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0051] Unless otherwise specified, the materials used in the present invention are all purchased by those skilled in the art, and the methods used in the present invention are all methods well known to those skilled in the art.

[0052] Example 1

[0053] 1. Materials and Methods

[0054] 1.1. Myofibrillar protein extraction

[0055] Using oval pomfret as raw material, the oval pomfret meat was ground at 3000 r / min for 2 min in an ice bath, centrifuged at 8000 r / min at 4°C for 10 min in a low phosphate buffer (0.005 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O, 15.5 mmol / L Na2HPO4·12H2O, pH 7.5), and the supernatant was removed. The centrifugation step was repeated 3 times. The precipitate was centrifuged three times at 4000 rpm in a high phosphate buffer solution (0.6 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O, 15.5 mmol / L Na2HPO4·12H2O, pH = 7.0) for 10 minutes each time. The mixture was then stored in a 4°C refrigerator for 2 hours and then centrifuged at 10,000 rpm for 10 minutes at 4°C. The supernatant was collected in cold distilled water and precipitated at 4°C for 30 minutes. The precipitate was then centrifuged again at 10,000 rpm for 15 minutes each time at 4°C to collect the fish-derived myofibrillar protein (MP).

[0056] 1.2 Preparation of flaxseed gum-fish protein gel (FG gel)

[0057] MP was dispersed in a pre-cooled buffer solution (0.1 M NaCl, 4°C, final concentration of fish-derived myofibrillar protein was 0.5 g / g). Flaxseed gum (FG) was added at 0, 1.5, 2, 2.5, 3, 3.5, and 4% (w / w, final concentration) and homogenized at 10,000 rpm for 1 min. Sunflower oil was then added at 10% (w / w, final concentration) and homogenized at 12,000 rpm for 3 min. The resulting mixtures were labeled FG-0%, FG-1.5%, FG-2%, FG-2.5%, FG-3%, FG-3.5%, and FG-4%, or as FG-0%, FG-1.5%, FG-2%, FG-2.5%, FG-3%, FG-3.5%, and FG-4% gel systems. The samples were heated in a 90°C water bath for 30 min, then cooled in an ice bath for 1 h and stored at 4°C for subsequent analysis.

[0058] 1.3 Preparation of lycopene-loaded flaxseed gum-fish protein gel (LFG gel) and determination of its embedding efficiency

[0059] Lycopene powder was weighed and dissolved in sunflower oil to a lycopene concentration of 1 mg / g, and magnetic stirring was applied for 4 h. MP was dispersed in a pre-cooled buffer solution (0.1 M NaCl, 4°C, fish-derived myofibrillar protein concentration of 0.5 g / g), and 1.5, 2, 2.5, 3, 3.5, and 4% (w / w, final concentration) of flaxseed gum were added, respectively, and homogenized at 10,000 rpm for 1 min; then, 10% (w / w, final concentration) of lycopene-dissolved sunflower oil was added and homogenized at 12,000 rpm for 3 min. The samples were labeled as LFG-1.5%, LFG-2%, LFG-2.5%, LFG-3%, and LFG-3.5%, respectively. and LFG-4%, or sequentially designated as LFG-1.5% gel system, LFG-2% gel system, LFG-2.5% gel system, LFG-3% gel system, LFG-3.5% gel system, and LFG-4% gel system; except for the final concentration of flaxseed gum, the final concentrations of the remaining components of these gel systems were the same: the final concentration of fish-derived myofibrillar protein was 20% (w / w), and the final concentration of lycopene-dissolving sunflower oil was 10% (w / w). Samples were heated in a 90°C water bath for 30 minutes and then cooled in an ice bath for 1 hour. They were stored at 4°C until further analysis.

[0060] Lycopene entrapment efficiency determination: 0.1 g of gel sample was added to 1 mL of DMSO and mixed evenly. Then, 2 mL of a mixed organic phase solution (n-hexane: dichloromethane = 3:1, v / v) was added for extraction. After three extractions, the extracts were combined and centrifuged at 3000 rpm for 10 min. The supernatant was placed in a spectrophotometer and the absorbance at 472 nm was measured. According to the lycopene standard curve (weigh 2.5 mg of lycopene standard, dissolve it in a small amount of dichloromethane, add n-hexane to make up to 50 mL, this is mother solution No. 1 (50 μg / mL), then take 0.1 mL, 0.2 mL, 0.4 mL, 0.8 mL, 1.6 mL, and 3.2 mL of standard solution from mother solution No. 1, respectively, dilute to 10 mL, shake well, and prepare standard solutions of 0.5, 1, 2, 4, 8, and 16 μg / mL. Measure the absorbance of the standard solution at 472 nm, and the standard curve is: Y (absorbance) = 0.0495 x (concentration) - 0.0077, R 2 =0.9995), and the lycopene content in the gel sample was calculated.

[0061] 1.4. Determination of surface hydrophobicity

[0062] Weigh 1 g of gel sample and mix it with 1 mL of distilled water. After vortex homogenization, add 200 μL of bromophenol blue solution and shake at room temperature in the dark for 10 minutes. Subsequently, centrifuge at 8000g for 10 minutes at 4°C, and collect the supernatant. The absorbance of the supernatant at a wavelength of 596 nm is measured using a spectrophotometer (SYNERGYH1 Bio Tek, USA), marked as A1. Distilled water is used as a control, and the measured absorbance is A0. The surface hydrophobicity is calculated according to the following formula:

[0063] Surface hydrophobicity (BPB bound, μg) = 200 μg × (A0-A1) / A0.

[0064] 1.5 Intermolecular Interactions

[0065] 0.5 g of gel sample was mixed with 4.5 mL of S1 (0.6 mol / L NaCl), S2 (0.6 mol / L NaCl and 1.5 mol / L urea), S3 (0.6 mol / L NaCl and 8 mol / L urea), or S4 (0.6 mol / L NaCl, 8 mol / L urea, and 0.5 mol / L β-mercaptoethanol) solutions, respectively, and incubated at 4°C for 1 hour. The mixture was centrifuged at 10,000 rpm for 10 minutes at 4°C, and the supernatant was collected. The protein concentration of the supernatant was determined using the biuret method. The ratio of different chemical bonds in the gel sample is expressed as the ratio of the protein content dissolved by the different reagents to the total protein concentration.

[0066] 1.6 FT-IR spectroscopy analysis

[0067] The FG gel sample was first placed at -80°C for 24 hours and then freeze-dried. The dried gel sample was ground into powder and stored in a desiccator. The gel sample powder was mixed with potassium bromide powder and ground into thin slices for FT-IR analysis. The FTIR spectrum range was 4000-400 cm -1 , with a resolution of 4cm -1 , with an average of 32 scans in total.

[0068] 1.7 LF-NMR analysis

[0069] The water distribution and proton density of the gel samples were analyzed using LF-NMR (Suzhou Newmax Analytical Instrument Co., Ltd., Suzhou, China). A 4 g gel sample was weighed and equilibrated to room temperature before being placed in an NMR tube for measurement. The SR-CPMG sequence was: SW = 2000 kHz, SF = 19 MHz, O1 = 453037.23 Hz, P1 = 6.6 μs, P2 = 11.04 μs, RFD = 0.02 ms, RG1 = 10.0 dB, DRG1 = 3, PRG = 2, TE = 0.6 ms, NECH = 9000, number of inversion times = 20, and NS = 8.

[0070] The proton density of the gel was observed using magnetic resonance imaging (MRI). The grayscale images were converted into proton density-weighted color images (T2) using uniform pseudo-colorization using NMR Image Processing Version 3.0 software (Suzhou Newmark Analytical Instrument Co., Ltd., Suzhou, China).

[0071] 1.8 Rheological properties

[0072] The rheological properties of FG gel samples and LFG gel samples were measured using a HAAKE MARSⅢ rheometer (MARS 60, Thermo, Germany).

[0073] In the static rheological test, the shear rate was set at 0.1-100s -1 , the viscosity of the sample was measured at 25°C.

[0074] Amplitude sweep: The sample was scanned from 0.1% to 100% strain at a constant frequency of 1 Hz at 25°C. Large-amplitude oscillatory shear was scanned from 0.1% to 500% strain at a constant frequency of 1 Hz at 25°C. Data at 1%, 10%, 100%, and 500% strain were collected to generate Lissajous plots.

[0075] Frequency sweep: at a strain of 1% (within the linear viscoelastic region), the frequency was 0.1-100 Hz.

[0076] Creep recovery test: The gel sample was subjected to a stress of 10 Pa for 300 s, and then the stress was removed for 300 s before recovery, and the strain recovery was observed.

[0077] Three-stage thixotropy test (three-interval shear recovery test, 3ITT): in 1s -1 Sheared at a low shear rate of 180s, then at 100s -1 Shearing was continued for 90s at a high shear rate and then -1 Shearing was carried out at a low shear rate of 270s.

[0078] 1.9. Confocal laser scanning microscopy (CLSM) analysis

[0079] Laser confocal microscopy was used to observe the microstructure of the emulsion gels and to image the distribution of proteins and oil droplets within the gels. The polysaccharide (flaxseed gum), fish-derived myofibrillar proteins, and the oil phase (sunflower oil) were stained with fluorescent dyes (100 μL of Calcofluor White Strain, 100 μL of a 1 mg / mL Nile Blue solution in ethanol, and 100 μL of a 1 mg / mL Nile Red solution in isopropanol). The stained samples were placed on glass slides and observed and photographed under a laser confocal microscope as soon as possible.

[0080] 1.10 International Standard for Grading and Testing of Foods Swallowed (IDDSI)

[0081] LFG gel was tested and classified for dysphagia according to the International Dysphagia Standardization Initiative method.

[0082] Fork drop test: Use a smooth fork to lift the gel sample and observe its accumulation on the fork and its dripping between the teeth.

[0083] Spoon tilt test: Use a standard smooth spoon to scoop up the sample and observe the state of the food bolus on the spoon. Then slowly tilt the spoon to the side and observe the sliding state of the sample and the state of the spoon surface after the sample slides.

[0084] Fork Squeeze Test: Cut a gel sample of appropriate size and apply pressure to the sample surface with a fork to observe how well the sample retains its shape. The gel sample's deformation and particle size are then graded according to the IDDSI standard.

[0085] 1.11. 3D printing performance

[0086] The lycopene-loaded gel sample was loaded into a syringe connected to a 3D food printer (Shiyin Food Robot Technology Co., Ltd., Hangzhou, China). The printing temperature was maintained at 25°C for 1 h. The nozzle diameter was 0.8 mm, the nozzle movement speed was 15 mm / s, and the fill rate was 70%.

[0087] 1.12. In vitro dynamic digestion characteristics

[0088] Gel digestion in the elderly gastrointestinal tract was simulated using a dynamic human gastrointestinal in vitro digestion apparatus (Dynamic Human Gastrointestinal IV, DHSI-IV, Xiaodong Pro Health (Suzhou) Instrument Co., Ltd., Suzhou, China). The preparations of simulated saliva (SSF), simulated gastric fluid (SGF), and simulated gastric fluid (SIF), as well as relevant parameters for gastrointestinal digestion in the elderly, are detailed in Table 1. Subsequently, pepsin was added to SGF to a final pepsin activity of 3000 U / mL; pancreatin and bile salts were added to SIF to a final pancreatin activity of 250 U / mL, and the final bile salt concentration was 10 mM.

[0089] Table 1 Relevant components and concentrations of SSF, SGF and SIF

[0090] Element Concentration in SSF / mM Concentration in SGF / mM Concentration in SIF / mM KCl 15.1 6.9 6.8 <![CDATA[KH2PO4]]> 3.7 0.9 0.8 <![CDATA[NaHCO3]]> 13.6 25 85 NaCl - 47.2 38.4 <![CDATA[MgCl2(H2O)6]]> 0.15 0.12 0.33 <![CDATA[(NH4)2CO3]]> 0.06 0.5 - HCl 1.1 15.6 8.4 <![CDATA[CaCl2(H2O)2]]> 1.5 0.15 0.6

[0091] Before the experiment, the equipment and simulated digestive fluid were preheated to 37°C. The stomach rolling speed was 2 r / min, the pyloric dilation was 0-15 mm, the stomach was squeezed at 1 mm / s, and the squeezing depth was 20 mm. First, 100 g of sample was mixed with 100 mL of SSF for 2 minutes and stirred homogenously to simulate oral feeding. The sample mixture was then introduced into the dynamic in vitro digestion simulation system for in vitro dynamic gastric digestion and in vitro dynamic gastrointestinal digestion. The simulated dynamic gastric digestion and simulated dynamic gastrointestinal digestion lasted for 120 minutes and 180 minutes, respectively.

[0092] During the simulated dynamic gastric digestion process, the pH of the gel samples in the simulated stomach was measured using a pH meter at 20, 40, 60, 80, 100, and 120 min.

[0093] The gastric emptying rate (%) is defined as the percentage of the volume of chyme retained in the human stomach after digestion (mL) divided by the sum of the total gastric secretion (mL) during digestion and the initial food sample volume (mL). The gastric emptying process was analyzed and fitted using the Elashoff power exponential model optimized by Siegel et al. The formula for calculating the gastric content residual ratio is as follows:

[0094] y(t)=1-(1-e -kt ) β ;

[0095] Where y(t) is the residual ratio of gastric contents at time t (min); k is the gastric emptying rate of food per minute (1 / min); and β is the intercept of the fitting curve on the y-axis.

[0096] t 1 / 2 It is an important indicator to measure the gastric emptying rate, representing the half-emptying time of food in the stomach. The shorter the half-emptying time, the faster the emptying rate. 1 / 2The calculation formula is as follows:

[0097]

[0098] Where k is the gastric emptying rate of food per minute (1 / min); β is the intercept of the fitting curve on the y-axis.

[0099] 1.13. Release Behavior and Bioaccessibility of Lycopene

[0100] At sampling point A( Figure 8 a) Collect gastric digestion samples at 30, 60, 90 and 120 min to simulate dynamic gastric digestion; at sampling point B ( Figure 8 In step a), gastrointestinal digestion samples were collected at 60, 90, 120, 150, and 180 minutes of simulated dynamic gastrointestinal digestion. Lycopene release rates from the gel samples during simulated dynamic gastric and gastrointestinal digestion were analyzed using the lycopene content determination method described in step 1.3. Lycopene release data from the gel samples during gastrointestinal digestion were fitted to the zero-order, first-order, and Higuchi kinetic equations to investigate the release mechanism of lycopene from the gel.

[0101] Zero-order equation: M t / M ∞ =kt;

[0102] First-order equation: M t / M ∞ =1-exp(kt);

[0103] Higuchi equation: M t / M ∞ =kt 1 / 2 ;

[0104] In the above equation, M t / M ∞ represents the cumulative release fraction of lycopene in time t, while k represents the release rate. Different equations correspond to different transfer mechanisms.

[0105] The digestive fluid from the small intestinal stage was centrifuged at 5000 rpm for 15 minutes at 4°C, and the middle layer, the transparent micelle layer loaded with lycopene, was collected. The bioaccessibility of lycopene in the gel after in vitro digestion was calculated according to the following formula.

[0106]

[0107] Where C 胶束部分 and C 消化液 are the lycopene concentrations in the micellar fraction and digestive fluid, respectively.

[0108] 1.14 Data Analysis

[0109] All experiments were repeated three times. SPSS software (Version 22.0, SPSS Inc., Chicago, IL, USA) was used to analyze the statistical significance of the results.

[0110] 2. Results and Discussion

[0111] 2.1 Structural properties of flaxseed-protein gel

[0112] Surface hydrophobicity is often used to characterize the degree of exposure of hydrophobic groups inside proteins, and plays a key role in determining the functional properties of proteins. When flaxseed gum interacts with myofibrillar protein (FG gel), it triggers the reconstruction of the protein molecular structure, and the change in surface hydrophobicity becomes an important representation of this reconstruction process. Figure 1 It can be observed from a that the surface hydrophobicity of the flaxseed gum added group is significantly reduced compared to the non-added group (FG-0%). This phenomenon is attributed to the flaxseed gum polysaccharide chain forming a barrier on the surface of the myofibrillar protein molecule through the steric effect, which limits the contact of surface hydrophobic groups such as phenylalanine and leucine side chains with the external environment. The exposure of the hydrophobic groups is suppressed, thereby reducing the surface hydrophobicity of the gel. In addition, in the process of forming the three-dimensional network structure of the gel, flaxseed gum and myofibrillar protein are intertwined, changing the size and shape of the gaps in the network. The hydrophobic areas that may have been exposed on the surface are confined to the inside of the network and are difficult to contact with the outside world, which also contributes to the reduction of surface hydrophobicity.

[0113] FT-IR is an important technical means to analyze the interaction between molecular groups, and can reveal the characteristic law of flaxseed gum on the evolution of the secondary structure of myofibrillar protein. Figure 1 As shown in b, the gel sample is at 4000-400 cm -1 There are six characteristic absorption peaks in the range. Compared with the FG-0% group, the spectra of other gel samples do not show new absorption peaks, which indicates that myofibrillar protein and flaxseed gum do not form new covalent bonds. -1 and 2860cm -1 The two peaks at 1750 cm are derived from the stretching vibration of aliphatic CH (CH2 and CH3 groups), reflecting the exposure and rearrangement of the hydrophobic region of myofibrillar protein. -1 The absorption peak corresponds to the characteristic vibration of ester carbonyl C=O; 1470cm -1 The absorption peak at 1170cm is attributed to the bending vibration mode of CH2 / CH3, which is mainly derived from the aliphatic structure of protein or flaxseed gum. -1The characteristic peak at is closely related to the stretching vibration of the C-O-C glycosidic bond. In order to infer the changes in the secondary structure of the protein, the FG gel amide I band (1600-1700 cm -1 ) to analyze the conformational characteristics of ( Figure 1 Amide I band 1651-1660cm -1 1600-1639cm -1 、1661-1700cm -1 and 1651-1700cm -1 The subpeaks correspond to α-helices, β-sheets, β-turns, and random coils, respectively. Compared to FG-0%, the α-helix content of the gel decreased at FG addition levels of 1.5wt% to 3wt%, while the β-sheet ratio increased, indicating an unfolding of the protein structure and enhanced interactions between proteins. Flaxseed gum promotes the formation of β-sheets, leading to the unwinding of protein structures and the creation of conditions for cross-linking of protein molecules, ultimately forming a stable three-dimensional gel matrix. However, the α-helix content in the FG-3.5% gel system was higher than that in the FG-0% group, while the β-sheet content was lower. This may be due to the electrostatic shielding effect of high flaxseed gum inducing an increase in α-helices, promoting cross-linking between proteins and flaxseed gum, and thus enhancing the order of protein sequences within the gel system. Previous studies have shown that the β-sheet content in heat-induced protein gels is positively correlated with their hardness. Therefore, the decreased β-sheet content in the FG-3.5% gel system suggests that its texture may be more suitable for individuals with dysphagia. This concentration-dependent conformational switching effect provides a molecular-level design basis for regulating the balance between swallowing adaptability and nutrient carrier function.

[0114] 2.2 Rheological properties of flaxseed-protein gel

[0115] All gel samples exhibited typical shear-thinning properties, with apparent viscosity negatively correlated with shear rate ( Figure 2In the FG-0% gel system, the rod-shaped myosin or expanded segments in the MP often overlap and entangle, and their steric hindrance and intermolecular friction increase the viscosity of the system. However, the apparent viscosity of the FG-1.5% and FG-2% gel systems is higher than that of the FG-0% gel system, primarily due to the synergistic thickening effect induced by the entanglement of flaxseed gum and myofibrillar proteins. When the flaxseed gum addition level is increased to 2.5wt%, its steric effect significantly interferes with the self-assembly of myofibrillar proteins, disrupting the ordered connections between proteins and causing a breakdown of the three-dimensional network structure, resulting in the lowest viscosity. As the flaxseed gum addition level increases to 3wt%-4wt%, the flaxseed gum and myofibrillar proteins restructure the gel network through electrostatic interactions. The electrostatic repulsion between the negatively charged flaxseed gum and fish-derived myofibrillar proteins not only alters the molecular structure and surface charge of the proteins but also increases the resistance of the protein chains, ultimately increasing the viscosity of the FG gel system. As the shear rate increases, the structure of the FG gel system is disrupted by external forces, and the apparent viscosity decreases. At high shear rates, the viscosity of the gel system with added FG is lower than that of the FG-0% gel system, which can effectively reduce the ink extrusion pressure during the 3D extrusion molding process, thereby improving printing accuracy and molding stability.

[0116] Rheological multi-dimensional characterization revealed that the addition of flaxseed gum has a significant structure-activity relationship on the viscoelasticity of fish-derived myofibrillar protein. Amplitude sweep analysis showed that ( Figure 2 ac in), the G' and G" values of all FG gel systems in the low strain range of 0.1-1% maintain a linear viscoelastic response, and the network structure remains relatively stable. In the linear viscoelastic region, all FG gel samples show the characteristic that G' is greater than G", indicating that they mainly behave as semi-solid gels dominated by elasticity. When the strain exceeds the critical value, the high concentration flaxseed gum groups (FG-3% gel system, FG-3.5% gel system and FG-4% gel system) show characteristic type III nonlinear viscoelastic behavior, which is manifested as a decrease in G', while G" shows a dynamic evolution of first increasing and then decreasing in the nonlinear viscoelastic region. The decrease in G' and G" also reflects that the intermolecular interactions in the gel sample are destroyed and the network structure is broken under this strain. In addition, when the strain exceeds the linear viscoelastic region, tanδ shows a geometric increase, which proves the gradual strengthening of the viscous dissipation mechanism during the disintegration of the gel sample network. At high strain amplitude, the tanδ of the gel system with flaxseed gum added was higher than that of the FG-0% gel system, indicating that the addition of flaxseed gum could enhance the flow properties of the gel sample under high stress and reduce swallowing resistance.

[0117] The frequency scanning results show that with the increase of flaxseed gum addition, the G' and G" of the FG gel system both show a downward trend, but the FG gel system always maintains the solid-state characteristic that G' is greater than G" ( Figure 2d and e in the figure). This indicates that linseed gum reduces the elasticity of the FG gel network. The G' of the FG gel system exhibits frequency-dependent behavior, which may be due to the dynamic formation of physical crosslinks and entanglements, which gives the network more storage capacity during rapid deformation and also reflects that its network structure is more sensitive to changes in reaction rate. In the entire frequency scanning range, the tanδ of all gel systems is less than 0.5, indicating that the gel system is dominated by elasticity ( Figure 2 f). The figure shows that when the flaxseed gum addition level is ≥2.5wt%, the tanδ value of the gel system decreases with increasing frequency. At low shear frequencies, higher tanδ values facilitate the formation of a cohesive bolus in the oral cavity, reducing oral residue. However, at high shear frequencies, tanδ decreases, indicating that the gel system's increased elasticity resists fragmentation during rapid deformation, helping to maintain bolus integrity during swallowing and reducing the risk of fragmentation and pharyngeal residue.

[0118] Creep and recovery behavior characterize the anti-deformation properties and energy dissipation mechanism of gel samples under external forces. Generally speaking, when the gel network structure is tighter, its pore size is smaller and the distribution is more uniform. At this time, if an external force is applied to the network structure, the network tends to be more stable, making it difficult for the chain segments to migrate and the molecular chains to move. As a result, the internal friction of the gel is increased due to the limited displacement, thus improving the gel's anti-deformation ability. Figure 2 As shown in h, all gel samples exhibited similar creep recovery properties, undergoing transient deformation during stress loading and unloading, and all exhibited irrecoverable strain. From 0 to 180 s, when the gel samples were subjected to constant stress, their deformation increased with time. Compared to the FG-0% gel system, the addition of flaxseed gum increased the degree of deformation. The FG-3% gel system exhibited the greatest deformation, corresponding to its lowest G' within the linear viscoelastic region, indicating weak elastic properties. After stress removal from the gel system between 180 and 360 s, the deformation decreased over time and stabilized after reaching a certain value, indicating that the gel system exhibited viscous flow characteristics, but some irrecoverable deformation remained. Flaxseed gum increased the degree of deformation and exhibited good deformation recovery, indicating that the gel system could readily undergo moderate deformation under tongue pressure to facilitate passage through the constricted pharynx. Furthermore, its excellent deformation recovery effectively prevented excessive deformation and disintegration of the food bolus, ensuring its structural integrity during esophageal transit.

[0119] from Figure 2 As can be seen from the figure, in the first stage, the viscosity of the gel samples was relatively small, and the viscosity of the gel system with flaxseed gum was slightly lower than that of the FG-0% gel system. In the second stage, at a high shear rate (100s -1), the structure of the gel system is destroyed and the viscosity decreases significantly. This is because the high shear force destroys the three-dimensional network structure of the gel system, weakens the interaction between molecules, and leads to a decrease in viscosity. When the shear rate returns to 1s -1 , the viscosity of the FG gel system is restored. Among them, the viscosity of the FG-0% gel system, FG-1.5% gel system and FG2% gel system in the third stage is higher than that in the first stage, indicating that they have strong structural recovery ability and thixotropy. This helps to improve the accuracy of 3D printing and improve the resolution and quality of printed products. However, for people with swallowing disorders, this will cause the food to move slower in the esophagus and significantly prolong the swallowing process, which may cause discomfort and increase the risk of choking. Although the viscosity of the FG-2.5% gel system, FG-3% gel system, FG-3.5% gel system and FG-4% gel system in the third stage is slightly lower than that in the first stage, they still have good structural recovery ability and can maintain the shape and structure of 3D printed products.

[0120] 2.3 Microstructure of flaxseed-protein gel

[0121] Observation by laser confocal microscopy ( Figure 2 Figure j) provides a visual analysis of the microstructure and droplet distribution of the FG gel system. The blue, green, and red fluorescence signals correspond to the spatial distribution of flaxseed gum, oil phase, and myofibrillar protein components, respectively. In the FG-0% gel system, the oil droplets are irregularly round, large in size, and loosely distributed within the gel network. The large, uneven oil droplets indicate a lack of effective emulsification or stabilization mechanisms within the FG-0% gel system, preventing the oil phase from being uniformly dispersed into small droplets. The loose distribution of the oil droplets within the gel network indicates that the gel network lacks sufficient binding capacity for the oil phase, preventing the formation of a tightly ordered microstructure. This situation can lead to poor stability of the entire gel system, making it prone to breakage during swallowing and increasing the risk of choking. The introduction of flaxseed gum significantly reduces the size of the oil droplets in the gel system, leading to a tighter spatial arrangement. This structural transformation is attributed to the rapid adsorption of the flaxseed gum-fish-derived myofibrillar protein complex to the oil-water interface under homogenization, forming a thicker charged layer interface. This interface generates strong electrostatic forces and spatial repulsion between the oil droplets, thereby changing their distribution. Simultaneously, the continuity and density of the gel network create a rigid confined space for the oil droplets. This not only effectively improves the encapsulation efficiency of functional factors but also imparts excellent structural fidelity to the 3D-printed material. Furthermore, the synergistic effect of uniform oil droplet distribution and enhanced interfacial adsorption ensures rapid deformation of the food bolus under low-shear triggering during swallowing. At the same time, maintaining an appropriate elastic modulus prevents premature structural collapse, making the gel system compatible with the physiological and mechanical requirements of people with swallowing dysfunction.

[0122] 2.4. Encapsulation efficiency of lycopene in flaxseed gum-protein gel

[0123] Through the molecular structure regulation of flaxseed gum, the network characteristics and physicochemical properties of myofibrillar protein gel are significantly enhanced, proving that it has dual-functional application potential in the field of dysphagia food bolus construction and food 3D printing. In order to further improve the nutritional properties of swallowing-adaptive gels, the present invention constructs a nutritionally fortified composite system through a lycopene loading strategy - a lycopene-loaded flaxseed gum-MP gel system (LFG gel system). Since the LFG-0% gel system without flaxseed gum cannot effectively encapsulate lycopene, the relevant results of the LFG-0% gel system are not shown. As Figure 3 As shown in a, with the increase in the amount of flaxseed gum added, the lycopene encapsulation rate showed an overall upward trend, which clearly shows that flaxseed gum played a positive and key role in the encapsulation process of lycopene. The addition of flaxseed gum can induce the enhanced effect of polysaccharide-protein interaction, build a more stable gel network, and then provide more space and sites to encapsulate lycopene, thereby improving the encapsulation rate. At the low concentration stage (1.5wt%-2wt%), flaxseed gum and myofibrillar protein initially cross-linked to form a basic network framework. However, due to the weak intermolecular interaction force, the gel network density was poor. This weak interaction and loose network structure limited the gel's ability to encapsulate lycopene. Therefore, the lycopene encapsulation rate (encapsulation efficiency) only increased from 73.10% to 74.79%, an increase of 3.24%. The encapsulation rate of the LFG-2.5% gel system decreased abnormally, with the lowest lycopene encapsulation rate (72.37%). It is speculated that at this concentration, micro-domain phase separation occurs between flaxseed gum and protein molecules. This phenomenon disrupts the uniformity and continuity of the gel network, weakening the gel matrix's ability to bind lycopene. In the high-concentration region (3wt%-4wt%), hydrogen bonding interactions between the gel system molecules are enhanced, forming a more compact three-dimensional network structure. This dense three-dimensional network achieves a synergistic fixation of lycopene by enhancing steric hindrance and interfacial affinity. Under these conditions, the lycopene encapsulation efficiency can reach as high as 85.99%, demonstrating excellent encapsulation results.

[0124] 2.5 Intermolecular Interactions of Lycopene-Loaded Flaxseed-Protein Gel

[0125] The intermolecular forces of the LFG gel system show nonlinear dynamic characteristics as the concentration of flaxseed gum evolves. Figure 3As shown in Figure 2b, ionic bonds dominate the formation of the LFG gel network. This is due to the electrostatic attraction between the anionic groups carried by flaxseed gum and the cationic sites of the protein. Within the low concentration range (1.5wt%-2wt%), the ionic bond content increases with increasing flaxseed gum content. This indicates that the appropriate introduction of flaxseed gum can provide more charged groups, promoting the formation of ionic bonds. However, when the FG addition amount increases to 2.5wt%, the ionic bond content in the gel system decreases by 40.16%. In contrast, hydrogen bonding and hydrophobic interactions increase by 72.14% and 35.53%, respectively. This change may be due to the fact that flaxseed gum at this concentration disrupts the original electrostatic balance of the LFG gel system and inhibits the formation of ionic bonds. At the same time, flaxseed gum promotes the structural rearrangement of fish-derived myofibrillar proteins, making it easier for intermolecular polar groups to form hydrogen bonds, thereby enhancing hydrogen bonding. In addition, the change in the distribution of hydrophobic regions in the gel system also promotes the enhancement of hydrophobic interactions. As the amount of flaxseed gum added further increased (3wt%-4wt%), the hydrogen bond network continued to strengthen. This may be because the densification of the polysaccharide chain triggered the interfacial water rearrangement effect, which increased the contact probability between the polar groups connected by water bridges. However, the hydrophobic interaction showed a downward trend. It is speculated that the flaxseed gum polysaccharide chain produced a spatial shielding effect, which reduced the accessibility of the hydrophobic groups. In addition, the disulfide bond content in the LFG gel system was in a fluctuating state, which may be related to the changes in the protein molecular conformation caused by the change in flaxseed gum concentration and the changes in the redox environment in the gel system. When the flaxseed gum addition amount increased to 2.5wt%, the disulfide bond content increased from 13.24% (LFG-2% gel system) to 20.09%. This may be because the protein conformation in the LFG-2.5% gel system unfolded, exposing more thiol groups, thereby achieving the reconstruction of the network structure. However, after the LEF gel system with a high concentration of flaxseed added was densified, the disulfide bonds were gradually replaced by hydrogen bonds.

[0126] 2.6 Water status and distribution

[0127] LF-NMR often analyzes the mobility of water molecules in gels by measuring the T2 relaxation time. The relaxation time T2 distribution curve of the gel is as follows: Figure 3 As shown in c in the figure, it can be seen that each sample has three peaks, which represent three types of water with different properties in the order of relaxation time, namely T 21 (bound water), T 22 (immobilized water) and T 23 (free water). With the increase of flaxseed gum content, the T2 peak of LFG gel system shifts to a lower relaxation time, which indicates that the mobility of water molecules decreases. This phenomenon is due to the increase in protein cross-linking density induced by flaxseed gum, which in turn builds a dense network structure. In the LFG-3.5% gel system, T 21The value of is the lowest and the peak area ratio is higher than that of other groups. This indicates that at this concentration, the three-dimensional network forms a high-strength binding effect with water molecules through polar groups, that is, the interaction between flaxseed gum and fish-derived myofibrillar protein has a significant effect on bound water, effectively binding water molecules to specific locations. 22 As the amount of flaxseed gum added increases, the water content shows a downward trend. This phenomenon confirms that flaxseed gum can promote the gel system to tightly capture water molecules and limit their migration. 22 The decrease is mainly attributed to the continuous strengthening of the non-covalent interaction between flaxseed gum and water molecules, which restricts the rotation, translation and other movements of water molecules. 23 The peak area ratio with the largest value indicates that the water in the gel system mainly exists in the form of free water. As the amount of flaxseed gum added increases, the T 23 The peak area showed a downward trend, which may be due to the interaction between water molecules and the hydrophilic groups of protein and flaxseed gum. This means that a large amount of free water is attracted by myofibrillar protein molecules or captured by the fish-derived myofibrillar protein gel network.

[0128] Magnetic resonance imaging (MRI) uses magnetic fields and radio frequency pulses to measure the density and relaxation time of hydrogen nuclei (protons) in gels. It is an effective visualization method for studying the water distribution in protein gels. The size and distribution differences of the red spots in the pseudo-color image can reflect the differences in the distribution of water molecules in the gel ( Figure 3 (di in the image). Red areas in the image indicate stronger resonance signals and higher hydrogen proton density, positively correlating with the water content embedded in the gel system. The red areas in the FG-3.5% gel system exhibit evenly distributed honeycomb-like signal patches, presumably due to the denser and more ordered network structure. This suggests that at this concentration, the optimization of the gel architecture by flaxseed gum not only affects water mobility but also results in a more uniform distribution of water within the gel, which has positive implications for the application of gel systems in dysphagia-prone foods and 3D-printed foods.

[0129] 2.7 Rheological properties of lycopene-loaded flaxseed-protein gel system (LFG gel system)

[0130] Rheological properties play a key role in regulating the extrusion fluidity and structural stability of food 3D printing inks. Ideal inks should exhibit shear-thinning properties, maintain a moderate elastic modulus to enhance self-supporting properties, have a moderate apparent viscosity to reduce friction with the nozzle, and possess a moderate creep recovery rate to ensure rapid recovery of apparent viscosity and modulus after extrusion. Figure 4Figure a shows that within the linear viscoelastic region, the G' of all LFG gel systems is higher than G", indicating that the lycopene-loaded flaxseed-protein gel system still exhibits elasticity-dominated gel properties. This property enables the gel system to maintain its shape and structure to a certain extent, which is beneficial for maintaining the stability of the printed structure during 3D printing. As the strain increases, when the critical strain is exceeded, all LFG gel systems show a decrease in G' and G", indicating that the structure of the gel system will be destroyed under larger strains and its viscoelasticity will also change. Figure 4 Figures b and c are Lissajous curves of LFG gel systems prepared by adding different concentrations of FG. This is a method to visually reveal nonlinear viscoelastic properties. At low strain amplitudes, the elastic Lissajous curve of the LFG gel system presents a narrow elliptical shape ( Figure 4 (b) As the strain amplitude increases, the narrow ellipse gradually transforms into a parallelogram, indicating that the LFG gel system changes from elastic to plastic behavior. This means that under different strain conditions, the mechanical behavior of the gel will change. At high strain, its plastic deformation ability will increase, which may affect the accuracy and shape retention of 3D printing. Figure 4 The viscosity Lissajous curve of c in the figure gradually shifts from an elliptical shape to a spindle shape, indicating that the LFG gel exhibits shear-thinning behavior. This shear-thinning property facilitates smooth extrusion of the ink during 3D printing. During extrusion, the gel is subjected to shear forces, which reduces its viscosity and allows it to pass smoothly through the nozzle, reducing friction with the nozzle. At a strain of 500%, a secondary loop appears in the viscosity Lissajous curve. This is due to the rearrangement of the microstructure, resulting in the emergence of a new network structure. This indicates that the addition of flaxseed gum improves the microstructural stability of the LFG gel system at higher strains.

[0131] In the frequency range of 0.1-100 Hz, all LFG gel systems showed weak frequency dependence, and their G' was greater than G", which indicated that all LFG gel systems showed elastic characteristics ( Figure 5(a) The G' of the gel system initially increases and then decreases with increasing FG addition. When the flaxseed gum addition range is between 1.5wt% and 3wt%, the mechanical strength of the gel system increases. This is likely due to enhanced interactions between flaxseed gum and protein, as well as between proteins, promoting the formation of a stronger and more compact intermolecular network, thereby enhancing the mechanical strength of the gel system. This increased mechanical strength improves the gel's printing properties, enabling it to better retain its shape during 3D printing and reducing deformation and collapse. However, when the FG addition exceeds 3.5wt%, the G' of the gel system decreases. This is presumably due to the excessive amount of flaxseed gum impairing protein-protein interactions. Excessive flaxseed gum molecules interfere with the normal interactions between protein molecules, disrupting the originally formed stable intermolecular network and reducing the mechanical strength of the gel system. Notably, the G' and G" of the 1.5% LFG gel system are significantly lower than those of the other groups. The higher G' and G" of the other groups are primarily attributed to protein-FG and protein-protein interactions. This interaction promotes the formation of a stronger and tighter intermolecular network structure in the gel system. When tanδ is higher than 1, the gel system exhibits more viscosity, while when tanδ is lower than 1, the gel system exhibits more solid-like properties. With the exception of the LFG-1.5% gel system, the remaining LFG gel systems have a tanδ < 0.5 over the entire frequency sweep range, demonstrating good 3D printing potential. Because a lower tanδ means that the gel system is more inclined to exhibit solid-like properties, it has better elasticity and structural stability, which meets the requirements of 3D printing for inks and can better maintain shape and structure during the printing process, which is conducive to achieving high-quality 3D printing.

[0132] The viscosity of all LFG gel systems decreases with increasing shear rate, showing shear thinning phenomenon, and belongs to pseudoplastic fluid ( Figure 5 b). The shear thinning phenomenon can be attributed to the increase in shear rate, which destroys the aggregated particles and weakens the interaction between the particles, thereby reducing the apparent viscosity. The shear thinning behavior exhibited by the LFG gel system has a positive effect on patients with dysphagia. During the swallowing process, food is subjected to shear forces in the mouth and throat. Because the LFG gel system has shear thinning properties, the viscosity decreases and the fluidity increases when subjected to shear force, making it easier to swallow. This helps to reduce the resistance of patients with dysphagia when eating, reduces the risk of aspiration, and improves the safety and smoothness of swallowing. At low shear frequencies (0.1-10s -1), when the amount of flaxseed gum added is in the range of 1.5wt%-3wt%, the viscosity of the LFG gel system increases with the increase of the amount of FG added. This may be because flaxseed gum can increase the viscosity of the continuous phase, and at the same time, the particles wrapped between the droplets of the gel system increase and aggregate, thereby hindering the movement between the droplets. However, when the amount of FG added is increased to 4wt%, the viscosity of the LFG gel system decreases instead. The reason may be that when the amount of FG added exceeds a certain value, the structure in the gel system cannot be further enhanced, and because flaxseed gum itself has a strong gelling effect. Therefore, when the flaxseed gum content is high, the gelling effect of the LFG gel system is dominated by flaxseed gum.

[0133] Creep testing can identify the cross-linking characteristics within the gel system on a longer time scale. Figure 5 Figure c shows the effect of FG concentration on the creep and recovery behavior of the gel system. Except for the LFG-1.5% gel system, all gel samples have similar creep curves, which reflects the typical viscoelastic fluid properties. The LFG-3% gel system has the lowest maximum creep value, which indicates that the gel network has strong cohesion and good deformation resistance. When the stress is removed, some deformations cannot be fully recovered due to irreversible strain. For 3D printing inks, high elasticity and strong strain resistance are beneficial to their deposition in subsequent layers and reduce damage during the printing process. However, excessive strain resistance is not friendly to people with dysphagia and will significantly increase their risk of choking. Therefore, 3D printed food for people with dysphagia needs to find a balance between the high elasticity and strain resistance required for 3D printing and the safety of people with dysphagia.

[0134] The three-stage thixotropy test reflects the ability of different gel samples to recover their structure after shearing, which can tell the possibility of different gel samples being used as 3D printing bioinks. Figure 5 d in Figure 4 shows that all gel samples were subjected to different shear rates (low 1s -1 , high speed 100s -1 and low 1s -1) changes in viscosity. In the first stage, the LFG gel system exhibited a relatively high viscosity, among which the viscosity value of the LFG gel system with an FG addition of 2.5wt%-4wt% was relatively stable. When the shear rate of all gel samples increased from low to high, the viscosity decreased significantly due to the shear thinning effect. This simulated the moment when the gel system passed through the 3D printing nozzle. However, when the shear rate decreased from high to low, the viscosity recovered rapidly, indicating that the gel system recovered sufficient mechanical strength after passing through the nozzle to support subsequent multi-layer loads. With the exception of the LFG-1.5% gel system, the final viscosity of the other gel systems after shear was slightly lower than the initial value. This may be because the strong shear force destroyed the network structure of the gel system, and the reconstruction of the gel system requires a lot of energy and time, so it is difficult to restore the initial viscosity.

[0135] 2.8. Confocal laser scanning microscopy (CLSM) analysis results

[0136] The difference in the microstructure of the gel system will affect the rheological properties of the gel, the embedding and release functions of the active substances, etc. From the CLSM image of the LFG gel system ( Figure 5 In figure e), it can be found that with the increase in the amount of flaxseed gum added, the gel network results become denser, which indicates that the interaction between flaxseed gum and fish-derived myofibrillar protein increases with the increase of flaxseed gum content. The chemical bonds (such as hydrogen bonds, ionic bonds, etc.) formed between flaxseed gum and the myofibrillar proteins in the gel system will cause the gel network to gradually densify. A denser network structure will give the gel system better stability and lycopene encapsulation capacity. The increase in the amount of flaxseed gum added also makes the oil droplets smaller and more evenly distributed. The uniform distribution of oil droplets helps to improve the rheological properties of the LFG gel system, helps to improve the texture and taste of foods with dysphagia, and reduces the risk of aspiration. In addition, for 3D printed foods, a uniform structure is beneficial to the stability of the printing process and the quality of the printed products.

[0137] 2.9. International Food Swallowing Standard Grading and Testing (IDDSI) Results

[0138] IDDSI provides a global standard test method to evaluate foods designed for people with dysphagia. Therefore, the fork drop test, spoon tilt test and fork squeeze test were performed to evaluate the potential of the LFG gel system as a food for people with dysphagia. Figure 6The fork drop test results in Figure a show that the LFG gel systems can maintain their shape on the fork. The LFG-1.5% gel system aggregates on the fork tip to form larger droplets but does not fall, exhibiting a pudding-like consistency. Highly thickened fluids or pudding-like foods can minimize the flow of food during swallowing, improving swallowing safety. The fork-spoon tilt test can be used to evaluate the viscoelastic properties of the sample. As can be seen from the figure, the LFG-1.5% gel system and the LFG-2.5% gel system retain more residue on the spoon during the tilting process. Both gel systems can maintain a fixed shape on the spoon, but when tilted and gently shaken, more sample residue remains on the spoon, indicating that they are highly viscous and unsuitable as a diet for patients with dysphagia. This is because foods with high viscosity increase the risk of choking for patients with dysphagia. The LFG-2%, LFG-3%, LFG-3.5%, and LFG-4% gel systems retained their shape on the spoon and slid easily off the spoon with a tilt and gentle shake, leaving virtually no sample residue. This indicates that these four gel systems are easy to swallow and do not stick to the tongue or throat. In a fork crush test, the LFG-3% and LFG-3.5% gel systems were easily crushed by the fork (without enough pressure to cause fingernail whitening). Their shapes remained intact after the fork was lifted, and the pattern remained clearly visible. Therefore, these two gel systems are classified as Class 5 chopped moist foods, requiring only light chewing and no biting. In contrast, the LFG-4% gel system required pressure equivalent to fingernail whitening to deform and did not immediately return to its original shape after the pressure was removed. Therefore, it is classified as Class 6 easy-to-swallow foods. In summary, the addition of flaxseed gum effectively improves the textural properties of the LFG gel system, making it suitable for people with swallowing difficulties.

[0139] 2.10 3D Printing

[0140] Printability and shape stability are crucial aspects of food 3D printing performance, providing crucial criteria for evaluating the printing results of different gels. Metrics such as distinct layers, clear textures, and strong printability are crucial for measuring the quality of 3D printed products, directly impacting their appearance and practicality. Figure 6Figure b shows the 3D printing results of LFG gels prepared with varying flaxseed gum concentrations. The low G' and viscosity of the LFG-1.5% gel system resulted in excessive ink extrusion from the nozzle during printing. After depositing on the platform, the ink failed to quickly recover its solid state, leading to product collapse and poor printing performance. This demonstrates that appropriate G' and viscosity are essential for successful 3D printing. Excessively low G' and viscosity make the gel ink difficult to control and form during printing. Other gel samples, on the other hand, flowed smoothly and continuously from the nozzle during 3D printing, demonstrating good deposition. However, the printing quality of LFG gel inks with different flaxseed gum concentrations varied. The petals printed with the LFG-2% gel system exhibited poor shape retention, with partial collapse and unclear texture, indicating insufficient shape stability at this concentration. With increasing flaxseed gum addition, the petals printed with the LFG gel ink retained their shape more completely, with distinct line layers and clear surface textures. Among them, the ink with the LFG-3.5% gel system performed the best, with excellent shape retention, no collapse, and clear lines. This indicates that the increased flaxseed gum concentration has a positive effect on improving the viscoelasticity of the LFG gel system ink. The higher viscoelasticity allows the gel ink to better maintain its shape during the printing process, reducing deformation and collapse, resulting in better printing performance. Compared to paste-like or pureed foods, the 3D-printed LFG-3.5% gel system has an attractive appearance, which is particularly meaningful for patients with dysphagia. A good appearance may increase patients' appetite and enhance their enjoyment of eating such foods, helping to improve their eating experience and potentially have a positive impact on their nutritional intake and mental health. It also demonstrates the advantage of 3D printing technology in preparing foods for dysphagia, namely, the ability to meet the specific needs of patients through personalized design.

[0141] 2.11. In vitro dynamic digestion characteristics of LFG gel system

[0142] The pH value changes of gel samples during dynamic gastric digestion are as follows Figure 7As shown in Figure a. Before adding the gel samples, the pH of fasting simulated gastric fluid was 3, simulating the fasting state of the elderly. During the initial phase (0-20 minutes), the gastric pH of the different LFG gel systems increased significantly from a fasting value of 3.0 to 6.28-6.58. This is due to the buffering effect of the gel system upon entering the stomach cavity through the esophagus and the consumption of gastric acid during gel decomposition. As dynamic gastric digestion time increased, gastric pH showed a downward trend. This is related to the continuous secretion of simulated gastric fluid and hydrochloric acid, as well as the decrease in the buffering capacity of the gel samples during gastric emptying. At 40 minutes of dynamic gastric digestion, the pH of the FG-1.5%, FG-2%, and FG-2.5% gel systems was relatively low, likely due to the low stability of the ionic and disulfide bonds in the gel structure in the acidic environment of the stomach. At 100-120 minutes of dynamic gastric digestion, the pH of the remaining gel systems, with the exception of the LFG-3% gel system, increased slightly. This may be because as digestion progresses, some components in the gel are gradually digested or broken down, and its buffering effect on gastric acid or other factors affecting acid value balance change.

[0143] During gastric digestion, the gel undergoes disintegration and dissolution through peristalsis and is then emptied into the duodenum. The gastric emptying characteristics of the gel system during dynamic gastric digestion mainly depend on the structural properties of the gel, such as size, texture, viscosity, microstructure, etc. Generally speaking, large and dense food particles take longer to become smaller in the gastric antrum, and therefore require a longer emptying time. The emptying rate of soft granular food is significantly faster than that of hard granular food. From the gastric emptying curve of the gel system in simulating the dynamic digestion process of the stomach in the elderly, it can be found that as the digestion time gradually increases, the retention rate in the stomach shows a gradually decreasing trend ( Figure 7 (b) After 120 minutes of dynamic gastric digestion, the LFG-4% gel system had the highest gastric retention rate, presumably due to the flaxseed gum-dominated gel system structure that inhibited emptying. This suggests that a high flaxseed gum content makes the gel system more compact, hindering the gel system's arrangement in the stomach. The correlation coefficients (R) of different gel samples and the Elashoff model fit were quantified. 2 ) is high, indicating that the model can better fit the gastric emptying process of the gel. According to the Elashoff model fitting results (Table 2), the β of the LFG-1.5% gel system, the LFG-2% gel system and the LFG-4% gel system is greater than 1, and delayed gastric emptying occurs, and the gastric retention rate at 20 minutes of gastric dynamic digestion is higher than that of other groups. This shows that the structural characteristics of these three groups of gels make it take longer for them to be ground into small particles that can pass through the pylorus in the stomach. The length of this lag time is closely related to the composition, texture and particle size of solid food. The gastric emptying rate constant (k) of the LFG-3.5% gel system is the highest, and t 1 / 2The lowest value indicates that the gel system has rapid emptying properties. This has positive implications for digestion in the elderly, as rapid emptying can reduce the burden on the stomach and avoid indigestion caused by food remaining in the stomach for too long. This suggests that the gel structure of the LFG-3.5% gel system may be more conducive to rapid grinding and passage through the pylorus in the stomach, and its texture, viscosity, and other structural properties may be more suitable for gastric digestion in the elderly.

[0144] Table 2 Elashoff model fitting results

[0145] deal with β(dimensionless) <![CDATA[K(min -1 )]]> <![CDATA[t 1 / 2 (min)]]> <![CDATA[R 2 ]]> LFG-1.5% 1.23697 0.01685 50.23 0.95246 LFG-2% 1.11435 0.01999 38.51 0.96418 LFG-2.5% 0.99315 0.01833 37.56 0.96034 LFG-3% 0.86627 0.01131 52.74 098193 LFG-3.5% 0.96591 0.02041 32.79 0.98192 LFG-4% 1.15353 0.01883 42.21 0.96209

[0146] Figure 7 Figure c shows gastric digesta images of gel samples collected at different times during the dynamic simulation of digestion. The gastric digesta appear dark orange because the structure of the gel sample is destroyed during digestion, and lycopene is released and dispersed in the gastric contents. As the digestion time increases, the color of the digesta gradually becomes lighter. This is because the emptying of the digesta in the stomach and the continuous secretion of gastric juice continuously dilute the lycopene in the gastric chyme, causing the color to become lighter. This phenomenon intuitively reflects the changes in the composition of gastric contents during digestion. From the microscopic structure diagram, it can be seen that as the dynamic gastric digestion time increases, the particle size in the gastric chyme continues to decrease, the oil droplets are more evenly distributed, and the content is relatively reduced ( Figure 7 (d) This indicates that gastric digestion gradually destroys the gel structure, refines the particles, and redistributes the oil droplets. This further illustrates the impact of gastric digestion on the gel microstructure, causing it to become increasingly uniform and fine, consistent with the general process of food breakdown and refinement during digestion. Compared to the gel's gastric digestate, the particle size and number of particles after gastrointestinal dynamic digestion were significantly reduced. This suggests that further digestion in the small intestine leads to more thorough breakdown and absorption of food, reflecting the gradual processing and transformation of the gel system throughout the digestive process. It also suggests that the digestive functions and synergistic effects of different gastrointestinal regions influence the degree of food digestion.

[0147] 2.12 Digestion Characteristics of Lycopene During In Vitro Dynamic Digestion

[0148] from Figure 8 The release curves of lycopene from the gel system during in vitro dynamic gastric digestion and in vitro dynamic gastrointestinal digestion can be seen in Figure 2. As the dynamic gastric digestion time increases, the amount of lycopene released increases, which is consistent with the law that substances are gradually released during normal digestion ( Figure 8b). During dynamic gastric digestion, the LFG-2% gel system achieved the highest lycopene release rate (30.79%) at 120 minutes, while the LFG-1.5% and LFG-3.5% gel systems exhibited significantly lower lycopene release rates than the other groups. This indicates that different flaxseed gum addition levels affect the encapsulation and release characteristics of lycopene. The slow release of lycopene during gastric digestion improves its bioavailability. Compared to gastric digestion, the lycopene release from the gel system after gastrointestinal digestion is significantly increased. This is because the small intestinal environment (such as bile salts) allows lycopene to form micelles, thereby promoting its absorption and utilization. Furthermore, during dynamic gastrointestinal digestion, the LFG-1.5% and LFG-3.5% gel systems maintained high release rates of 51.17% and 49.85%, respectively, even after 180 minutes of gastrointestinal digestion.

[0149] To further investigate the release of lycopene during in vitro dynamic gastric digestion and in vitro dynamic gastrointestinal digestion, the release process of lycopene was analyzed using zero-order, first-order, and Higuchi models. The dynamic parameters of lycopene release from the gels obtained through model fitting are shown in Table 3. The data clearly show that the release curves of the gel samples closely matched the applied models. During dynamic gastric digestion, the release curves of the gel systems, with the exception of the LFG-3.5% gel system, had the highest correlation coefficients with the first-order dynamic model, indicating that during in vitro dynamic gastric digestion, lycopene release was dominated by passive diffusion driven by the concentration gradient at the gel-gastric fluid interface. The release curve of the LFG-3.5% gel system during gastric digestion closely matched the Higuchi model, indicating that the release of lycopene from the LFG-3.5% gel system follows a swelling-diffusion mechanism. This may be related to the swelling properties of the gel system in the stomach, which allows the lycopene to diffuse gradually, thus achieving delayed release. During dynamic gastrointestinal digestion, the release of lycopene from most LEG gel systems conformed to the Higuchi model based on Fichian diffusion, indicating that diffusion remains an important mechanism for lycopene release during gastrointestinal digestion. The release of lycopene from the LFG-3.5% gel system during dynamic gastrointestinal digestion approximated a zero-order model, meaning that lycopene release was controllable and released at a constant rate. Furthermore, the release behavior of the LFG-3.5% gel system during dynamic gastrointestinal digestion depended on the gradual degradation of the gel and was independent of concentration. This suggests that the gel structure of the LFG-3.5% gel system gradually degrades at a relatively stable rate during gastrointestinal digestion, resulting in a constant release rate of lycopene. This property has potential advantages for controlling the release of lycopene and improving its bioavailability.

[0150] Table 3 Correlation coefficients (R) of lycopene in gel obtained after fitting different models 2 )

[0151]

[0152]

[0153] from Figure 8 As shown in Figure d, a complex dynamic regulatory relationship exists between the amount of flaxseed gum added and the bioaccessibility of lycopene during dynamic gastrointestinal digestion. In the low-concentration range (1.5wt%-2wt%) LFG gel system, lycopene bioaccessibility showed an upward trend during the 60-150 min of gastrointestinal digestion. This suggests that the loose gel network at this concentration favors the formation of mixed micelles between fatty acids and bile salts to dissolve lycopene, thereby enhancing lycopene bioaccessibility. However, at the end of the 180-min digestion phase, bioaccessibility showed a downward trend. This is likely due to the peak release in the early stages, which exceeded the instantaneous loading capacity of the micelles, resulting in the oxidative loss of some unbound lycopene through precipitation. For the LFG-2.5% gel system, the bioavailability plummeted to 64.67% at 120 min of digestion. This phenomenon may be due to changes in the gastrointestinal environment, which triggers local network collapse, exposing lycopene to the digestive environment and causing degradation. The LFG-3.5% gel system maintained a relatively stable bioaccessibility (81.07%) throughout the gastrointestinal digestion process. This is likely due to the appropriate gel crosslinking density, which allows it to match the dynamic encapsulation capacity of the micelles through a sustained-release mechanism while maintaining the network's resistance to digestive enzymes, thus avoiding late collapse. When the flaxseed gum addition was increased to 4 wt%, the high-density network initially excessively inhibited lycopene release, resulting in concentrated lycopene release during certain time periods. Therefore, the lycopene bioaccessibility of the LFG-4% gel system reached a maximum of 87.39% after 120 minutes of dynamic gastrointestinal digestion. However, due to the limited encapsulation efficiency of the micelles for lycopene, the bioaccessibility decreased to 75.14% after 150 minutes of gastrointestinal digestion. In summary, the LFG-3.5% gel system successfully achieved a dynamic balance between network strength and micelle encapsulation rate, and its stable release pattern better suited the physiological characteristics of the elderly population.

[0154] 2.13 Flaxseed Gum-Myofibrillar Protein Molecular Interaction Drives Dynamic Digestion-Controlled Release Mechanism

[0155] Flaxseed gum regulates the structure of myofibrillar protein gels through multiscale molecular interactions, achieving synergistic control from molecular conformational adaptation to digestive response properties. Flaxseed gum is an anionic heteropolysaccharide with abundant hydrophilic side chains. In solution, the exposed hydroxyl and carboxyl groups of the side chains provide abundant sites for intermolecular hydrogen bonding and charge interactions. At the molecular level, the anionic groups of flaxseed gum form complexes with the amino groups of myofibrillar protein through electrostatic interactions, disrupting the intrinsic hydrogen bonding network of myofibrillar protein and inducing a secondary structure transition from an α-helix to a β-sheet. This conformational shift drives the hydrophobic core into the interior of the molecule, reducing the surface hydrophobicity of the protein, thereby inhibiting the disordered stacking of thermally induced aggregates and constructing a stable elastic network. When flaxseed gum is added at 3.5 wt%, its electrostatic shielding effect weakens the ionic bonds between fish-derived myofibrillar proteins, inducing the formation of α-helices, and strengthening the weight of hydrogen bonding and hydrophobic interactions, forming a highly viscoelastic interpenetrating network. The dynamic balance between different interaction forces within the network gel system provides a molecular basis for the dynamic deformation of the bolus during swallowing. At the mesoscopic scale, the entanglement of the flaxseed gum backbone with the oil droplets through spatial synergistic confinement reduces the uneven distribution of the oil droplets and constructs a dense three-dimensional gel network. The dense gel network structure and the increased cross-linking density of myofibrillar proteins reduce the migration of water molecules, effectively confining the free water in the gel system due to the anchoring effect of the hydrophilic groups. The regulation of the water distribution of the LFG gel system by flaxseed gum not only prevents the texture degradation of the bolus caused by free water leakage during swallowing but also enhances the encapsulation capacity of lycopene. At the digestive response level, the acidic gastric digestive environment triggers the protonation of the flaxseed gum carboxyl groups, resulting in a conformational contraction. This enhances the electrostatic attraction between the flaxseed gum and the fish-derived myofibrillar proteins, forming a dense and stable composite structure that effectively delays the release of lycopene in the stomach. During dynamic gastrointestinal digestion, the ionization of carboxyl groups in the neutral environment of the small intestine stretches the molecular chains and generates swelling pressure, gradually relaxing the ordered network and triggering a Higuchi-type gradient diffusion of lycopene within the gel network. Its release rate dynamically matches the intestinal micelle embedding threshold. When flaxseed was added at a concentration of 3.5 wt%, the lycopene release behavior of the gel system fitted the zero-order equation even better, indicating that the LFG-3.5% gel system exhibits a smoother release process during gastrointestinal digestion, primarily due to the disintegration of the gel structure, achieving a dynamic match between release kinetics and micelle embedding threshold. Cross-scale coupling of rheological and swallowing properties further validates the functional adaptability of the gel. Shear-thinning properties ensure low resistance to deformation under swallowing stress, while thixotropic recovery restores structural rigidity during esophageal transit, achieving a dynamic balance between "squeezing, deformation, and anti-collapse." Combined with IDDSI test results and 3D printing performance, the LFG-3.5% gel system is classified as a Class 5 easy-to-swallow food and exhibits high printing accuracy.In summary, flaxseed gum breaks through the contradiction between mechanical strength, texture adjustability and functional factor delivery efficiency of traditional protein gels through the triple mechanisms of structural adaptation at the molecular level, phase behavior regulation at the mesoscopic scale, and dynamic response of macroscopic functions, providing a reference for the development of gel foods for the elderly that are both safe to swallow and have precise nutrition.

[0156] 3. Conclusion

[0157] This invention constructs a flaxseed gum and fish-derived myofibrillar protein composite gel system through a multiscale structural manipulation strategy, providing theoretical and technical support for 3D printing technology and precision nutrient delivery for elderly patients with dysphagia. At the molecular level, flaxseed gum induces a rearrangement of the myofibrillar protein secondary structure, remodeling the gel's hydrogen-bonding network. This remodeling of the gel network drives the myofibrillar protein secondary structure from α-helices to β-sheets, reducing the protein's surface hydrophobicity and effectively inhibiting the formation of coarse protein aggregates induced during heating. Furthermore, this network rearrangement optimizes the uniformity of oil droplet distribution within the gel system and significantly enhances the entrapment efficiency of lycopene through the synergistic interaction of intermolecular polar groups. Macroscopic performance analysis demonstrates that the chain entanglement and electrostatic repulsion effects of flaxseed gum impart shear-thinning properties and thixotropic recovery to the gel system, making it suitable for the dual requirements of high-precision extrusion and structural conformality in 3D printing. The LFG-3.5% gel system was classified as a Class 5 easy-to-swallow food in the IDDSI test. The printed product is structurally complete and can be customized for complex shapes. In vitro dynamic digestion experiments simulating elderly individuals demonstrated that flaxseed gum effectively delayed the release of lycopene during gastric digestion, reducing its degradation risk in the acidic environment. During intestinal digestion, the gel network swells, promoting lycopene release and enhancing its bioavailability. The LFG-3.5% gel system exhibited the shortest gastric emptying time during in vitro dynamic gastric digestion, better aligning with the physiological characteristics of reduced gastric motility in the elderly and preventing the discomfort associated with prolonged gastric retention. This study innovatively integrated multiscale structural analysis with dynamic digestion modeling techniques to elucidate the cascade mechanism of "intermolecular force rearrangement, network morphology evolution, and digestive response." This research not only provides insights for the rational design of safe-to-swallow 3D-printed foods for the elderly but also opens up a biomimetic-driven technology path for the development of physiologically-based functional foods. Future research could further optimize the structure-function adaptation framework through digital modeling, expanding its potential for application in the co-delivery of multiple nutrients.

[0158] Example 2

[0159] When the addition amount of gellan gum or gum arabic is 0.5wt%-6wt% (the steps are the same as "1.3" in Example 1, except that gellan gum or gum arabic is used instead of flaxseed gum), the prepared gellan gum-myofibrillar protein gel and gum arabic-myofibrillar protein gel will show stratification during the heat induction process ( Figure 9 and Figure 10 ).

[0160] The fish-derived protein gel system prepared by using polysaccharides such as locust bean gum and guar gum (the steps are the same as "1.3" in Example 1, the only difference is that locust bean gum or guar gum is used to replace flaxseed gum). These polysaccharides have poor compatibility with myofibrillar protein. At high concentrations, phase separation occurs between the polysaccharide and the gel, and a uniform gel cannot be formed. At low concentrations (less than 1wt%), locust bean gum and guar gum can form a uniform gel with myofibrillar protein. However, locust bean gum-fish-derived protein gel and guar gum-fish-derived protein gel do not meet the international dysphagia dietary standards. As shown in the figure, in the spoon tilt test, the gel sample still cannot fall smoothly after the spoon is tilted and gently shaken, and there is a lot of residue in the spoon. This shows that the two gels have high viscosity and are easy to adhere to the throat during swallowing, causing risks such as choking ( Figure 11 ).

[0161] Lycopene embedding efficiency of different gels ( Figure 12 ) It can be found that when the polysaccharide addition amount is 0.75wt%, the lycopene encapsulation efficiency of locust bean gum-protein gel (LG-0.75) and guar gum (GG-0.75) is significantly lower than that of flaxseed gum-protein gel (LFG-0.75).

[0162] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a 3D printed flaxseed glue fish protein gel adapted to the swallowing and biomimetic digestive response of the elderly, characterized in that: The following steps are involved: Using ovate pomfret as a raw material to prepare fish-derived myofibrillar protein, and uniformly mixing the fish-derived myofibrillar protein with a buffer solution to obtain a fish-derived myofibrillar protein solution; Evenly mixing lycopene and sunflower oil to obtain a lycopene solution; Evenly mixing the fish-derived myofibrillar protein solution and flaxseed gum to obtain a flaxseed gum-fish-derived protein gel; The lycopene solution and the flaxseed gum-fish source protein gel are evenly mixed to obtain the 3D printed flaxseed gum-fish source protein gel.

2. The preparation method according to claim 1, characterized in that The concentration of lycopene in the lycopene solution is 1 mg / g.

3. The preparation method according to claim 1, characterized in that The final concentration of the flaxseed gum in the 3D printed flaxseed gum fish-derived protein gel is 1.5-4 wt %, the final concentration of the lycopene solution is 10 wt %, and the final concentration of the fish-derived myofibrillar protein is 20 wt %.

4. The preparation method according to claim 1, characterized in that The buffer solution is a 0.1 M NaCl solution.

5. The preparation method according to claim 1, characterized in that The method for preparing fish-derived myofibrillar protein comprises the steps of sequentially grinding and centrifuging oval pomfret meat.

6. The preparation method according to claim 5, characterized in that The preparation method of the fish-derived myofibrillar protein specifically comprises the following steps: The oval pomfret meat is minced in an ice bath, and then centrifuged three times in a low phosphate buffer solution. The resulting precipitate is then centrifuged three times in a high phosphate buffer solution. The resulting supernatant is stored in a 4°C refrigerator for 2 hours and then centrifuged again. The resulting supernatant is mixed with distilled water and precipitated, and then centrifuged twice more to collect the precipitate to obtain the fish-derived myofibrillar protein.

7. The preparation method according to claim 6, characterized in that The low phosphate buffer comprises 0.005 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O and 15.5 mmol / L Na2HPO4·12H2O; The high phosphate buffer comprises 0.6 mol / L NaCl, 3.38 mmol / L NaH2PO·2H2O and 15.5 mmol / L Na2HPO4·12H2O.

8. A 3D printed flaxseed glue fish protein gel obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the 3D printed flaxseed glue fish protein gel according to claim 8 in the preparation of 3D printed food.

10. Use of flaxseed gum-fish protein gel in improving the embedding efficiency and / or bioaccessibility of lycopene, characterized in that: The preparation method of the flaxseed gum-fish protein gel comprises the following steps: Using ovate pomfret as a raw material to prepare fish-derived myofibrillar protein, and uniformly mixing the fish-derived myofibrillar protein with a buffer solution to obtain a fish-derived myofibrillar protein solution; The fish-derived myofibrillar protein solution and flaxseed gum are evenly mixed to obtain the flaxseed gum-fish-derived protein gel.

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