A 3D printed flaxseed gum fish protein gel adapting to swallowing and bionic digestion response of the elderly and a preparation method and application thereof

Abstract

This invention relates to the field of food processing technology, and in particular to a 3D-printed flaxseed gum-fish protein gel adapted to the swallowing and biomimetic digestive responses of the elderly, its preparation method, and its applications. This invention achieves multi-scale structural regulation and precise lycopene delivery by constructing a flaxseed gum-myofibrillar protein composite gel system loaded with lycopene, and systematically elucidates its functional adaptation mechanism in 3D-printed swallowable foods. This invention focuses on the molecular mechanism by which the rearrangement of flaxseed gum molecules drives the secondary structure transformation of myofibrillar proteins. Combined with the rheological recovery properties of LFG gel under dynamic shear conditions and the cross-scale regulatory effect of swallowing dynamics, it further reveals the lycopene release behavior in simulating the dynamic digestive process of the elderly. From the synergistic perspective of molecular interactions, rheological responses, and digestive behavior regulation, this invention provides a reference for the development of special dietary foods for the elderly that combine swallowing adaptability, precise nutrient delivery, and sensory palatability.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and in particular to a 3D-printed flaxseed gel fish protein gel adapted to the swallowing and biomimetic digestive response of the elderly, its preparation method and application. Background Technology

[0002] Traditional dysphagia-related foods rely on textural modifications such as thickening and fragmentation to ensure swallowing safety, but these methods suffer from drawbacks including nutrient density loss, low efficiency in delivering functional factors, and limited palatability. In recent years, 3D printing technology has provided a new pathway for the development of personalized dysphagia-related foods. By precisely controlling the rheological properties and morphological adaptability of materials, customized soft foods can meet the needs of different dysphagia patients. However, starch or single-protein gels suffer from limitations such as insufficient mechanical strength and limited nutrient carrier function, making it difficult to simultaneously meet the needs for swallowing safety and functional nutrient delivery. While polysaccharides such as carrageenan and konjac glucomannan can improve the water-holding capacity of myofibrillar protein gels, excessive use can lead to viscoelastic imbalance, increasing the risk of food bolus adhesion as it passes through the pharynx. Flaxseed gum, as a soluble dietary fiber, offers health benefits such as anti-diabetic, anti-hypertensive, cholesterol-lowering, and colorectal cancer prevention. Current technology suggests that flaxseed gum is a potential thickener for dysphagia patients, exhibiting good rheological and lubricating properties in different fluid matrices and increasing the pleasure of the final stage of swallowing. However, the multi-scale structural (molecular-mesoscopic-macroscopic) regulatory mechanisms of flaxseed gum-myofibrillar protein gel remain unclear. In particular, how polysaccharide-protein interactions affect the release kinetics of active ingredients through molecular rearrangement under dynamic digestion conditions requires systematic research.

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

[0004] The purpose of this invention is to provide a 3D-printed flaxseed gum-fish protein gel adapted to the swallowing and biomimetic digestive responses of the elderly, along with its preparation method and applications, to address the problems existing in the prior art. This invention provides a 3D-printed flaxseed gum-fish protein gel adapted to the swallowing and biomimetic digestive responses of the elderly, which can be used to prepare 3D-printed food products. This invention provides a reference for developing special dietary foods for the elderly that combine swallowing adaptability, precise nutrient delivery, and sensory palatability.

[0005] To achieve the above objectives, the present invention provides the following solution:

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

[0007] Fish-derived myofibrillar protein was prepared using oval pomfret as raw material. The fish-derived myofibrillar protein was then mixed evenly with a buffer solution to obtain a fish-derived myofibrillar protein solution.

[0008] Mix lycopene and sunflower seed oil evenly to obtain a lycopene solution;

[0009] The fish-derived myofibrillar protein solution and flaxseed gum were mixed evenly to obtain flaxseed gum-fish-derived protein gel.

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

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

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

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

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

[0015] Preferably, the method for preparing the fish-derived myofibril protein includes the steps of sequentially crushing and centrifuging the flesh of oval pomfret.

[0016] Preferably, the preparation method of the fish-derived myofibril protein specifically includes the following steps:

[0017] The oval pomfret meat was crushed under ice bath conditions, then centrifuged three times in low phosphate buffer, and the resulting precipitate was centrifuged three times in high phosphate buffer. The resulting supernatant was stored in a refrigerator at 4°C for 2 hours, and then centrifuged again. The resulting supernatant was mixed with distilled water and precipitated, and then centrifuged twice more. The precipitate was collected to obtain the fish-derived myofibril 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 solution comprises 0.6 mol / L NaCl, 3.38 mmol / L NaH2PO·2H2O and 15.5 mmol / L Na2HPO4·12H2O.

[0020] This invention provides a 3D-printed flaxseed gum fish protein gel obtained using the above-described preparation method.

[0021] This invention provides the application of the above-mentioned 3D printed flaxseed gum fish protein gel in the preparation of 3D printed food.

[0022] This invention provides the application of flaxseed gum-fish protein gel in improving the encapsulation rate and / or bioavailability of lycopene. The preparation method of the flaxseed gum-fish protein gel includes the following steps:

[0023] Fish-derived myofibrillar protein was prepared using oval pomfret as raw material. The fish-derived myofibrillar protein was then mixed evenly with a buffer solution to obtain a fish-derived myofibrillar protein solution.

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

[0025] More preferably, the method for preparing the fish-derived myofibrillar protein includes the steps of sequentially crushing and centrifuging the flesh of oval pomfret.

[0026] More preferably, the preparation method of the fish-derived myofibril protein specifically includes the following steps:

[0027] The oval pomfret meat was crushed under ice bath conditions, then centrifuged three times in low phosphate buffer, and the resulting precipitate was centrifuged three times in high phosphate buffer. The resulting supernatant was stored in a refrigerator at 4°C for 2 hours, and then centrifuged again. The resulting supernatant was mixed with distilled water and precipitated, and then centrifuged twice more. The precipitate was collected to obtain the fish-derived myofibril protein.

[0028] More 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 solution 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] This invention aims to develop functional 3D-printed foods suitable for elderly individuals with swallowing difficulties. By constructing a lycopene-loaded flaxseed gum-myofibrillar protein composite gel system (LFG gel, i.e., 3D-printed flaxseed gum-fish-derived protein gel), it achieves multi-scale structural regulation and precise lycopene delivery, while systematically elucidating its functional adaptation mechanism in 3D-printed swallowable foods. This invention focuses on the molecular mechanism by which the rearrangement of flaxseed gum molecules drives the secondary structure transformation of myofibrillar proteins. Combining the rheological recovery properties of LFG gel under dynamic shear conditions and its cross-scale regulatory effect on swallowing dynamics, it further reveals the lycopene release behavior in simulating the dynamic digestive process of the elderly. From the synergistic perspective of molecular interactions, rheological responses, and digestive behavior regulation, this invention provides a reference for developing special dietary foods for the elderly that combine swallowing adaptability, precise nutrient delivery, and sensory palatability.

[0032] In the 3D-printed flaxseed gum-fish protein gel provided by this invention, when the amount of flaxseed gum added is between 1.5wt% and 4wt%, especially at 3.5wt%, the flaxseed gum induces α-helical ascent through electrostatic shielding. Flaxseed gum promotes the formation of a dense elastic network, increasing the lycopene encapsulation rate to 85.99%. Furthermore, flaxseed gum optimizes the viscoelastic properties of the gel system through molecular chain entanglement, endowing the gel with good deformation capacity and self-support. This not only ensures the smooth passage of the gel during swallowing but also allows it to exhibit excellent recovery performance after undergoing high-speed shearing. This invention, using a biomimetic dynamic digestive system (DHSI-IV) to simulate the gastrointestinal environment of the elderly, found that the gel network undergoes conformational contraction in the gastric acid environment, delaying lycopene release. During dynamic gastrointestinal digestion, the lycopene release rate in this 3D-printed flaxseed gum-fish protein gel is increased, the oil droplet distribution in the digestate is more uniform, and the micellization process of lycopene is significantly promoted, with a bioavailability rate as high as 87.39%. According to the standards of the International Dietary Standards for Dysphagia Action Committee (IDDSI), LEF-3.5% gel is classified as a Level 5 food for dysphagia. This gel not only possesses excellent 3D printing performance but also closely matches the digestive characteristics of the elderly. This invention not only provides a theoretical basis for 3D-printed foods with swallowing safety but also offers a new approach to the synergistic regulation of "structure-function-digestive response" in addressing precision nutrition and functional food design for the elderly. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The surface hydrophobicity (a), FT-IR spectrum (b), and Gaussian distribution fitting curves (ci) of FG-0%-FG-4% for different formulation gel systems are shown.

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

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

[0037] Figure 4 The strain scans (a), elastic Lissajous curves (b), and viscous Lissajous curves (c) of the samples at strain amplitudes of 1%, 10%, 100%, and 500% are shown.

[0038] Figure 5 The results show the frequency scan (a), apparent viscosity (b), creep-recovery curve (c), 3ITT recovery curve (d), and microstructure (e) of the LFG gel sample.

[0039] Figure 6 Appearance of the 3D-printed gel for IDDSI testing (a) and (b);

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

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

[0042] Figure 9 Gellar gel-myofibrillar protein gel may exhibit stratification during thermal induction;

[0043] Figure 10 The gum arabic-myofibrillar protein gel exhibits stratification during the heat induction process.

[0044] Figure 11 The results of the spoon tilt test experiment;

[0045] Figure 12 The results of the investigation on the encapsulation rate of lycopene. Detailed Implementation

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of 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 terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0048] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0049] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

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

[0051] Unless otherwise specified, all materials used in this invention are commonly purchased by those skilled in the art, and all methods used in this invention are 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 crushed at 3000 r / min for 2 min under ice bath conditions, and then centrifuged at 8000 r / min at 4℃ for 10 min in low phosphate buffer (0.005 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O, 15.5 mmol / L Na2HPO4·12H2O, pH 7.5). The supernatant was removed, and the centrifugation step was repeated 3 times. The precipitate was centrifuged three times at 4000 rpm for 10 min each time in a high-phosphate buffer solution (0.6 mol / L NaCl, 3.38 mmol / L NaH2PO2·2H2O, 15.5 mmol / L Na2HPO4·12H2O, pH 7.0). The mixture was then stored at 4°C for 2 h, followed by centrifugation at 10000 rpm for 10 min at 4°C. The supernatant was collected in cold distilled water and precipitated at 4°C for 30 min. The precipitate was then centrifuged twice more at 10000 rpm for 15 min each time at 4°C, and the precipitate was collected; this was 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 (0.1M NaCl, 4℃, final concentration of fish-derived myofibrillar protein: 0.5 g / g). 0, 1.5, 2, 2.5, 3, 3.5, and 4% (w / w, final concentration) of flaxseed gum (FG) were added, and the mixture was homogenized at 10,000 rpm for 1 min. Then, 10% (w / w, final concentration) of sunflower seed oil was added, and the mixture was homogenized at 12,000 rpm for 3 min. These were subsequently labeled as FG-0%, FG-1.5%, FG-2%, FG-2.5%, FG-3%, FG-3.5%, and FG-4%, or sequentially labeled as FG-0%, FG-1.5%, FG-2%, FG-2.5%, FG-3%, FG-3.5%, and FG-4% gel systems. The sample was heated in a 90°C water bath for 30 min, then cooled in an ice bath for 1 h. It was then stored at 4°C for subsequent analysis.

[0058] 1.3 Preparation and Encapsulation Efficiency Determination of Lycopene-Loaded Flaxseed Gum-Fish Protein Gel (LFG Gel)

[0059] Lycopene powder was weighed and dissolved in sunflower seed oil to a concentration of 1 mg / g, and the mixture was magnetically stirred for 4 hours. Myofibrillar protein (MP) was dispersed in a pre-cooled buffer solution (0.1 M NaCl, 4℃, fish-derived myofibrillar protein concentration of 0.5 g / g). Flaxseed gum was added at concentrations of 1.5%, 2%, 2.5%, 3%, 3.5%, and 4% (w / w, final concentration), and homogenized at 10,000 rpm for 1 min. Then, 10% (w / w, final concentration) of sunflower seed oil containing dissolved lycopene was added, and the mixture was homogenized at 12,000 rpm for 3 min, and these concentrations were subsequently labeled LFG-1.5%, LFG-2%, LFG-2.5%, LFG-3%, and LFG-3.5%. The gel systems were prepared as follows: LFG-4%, or sequentially designated as LFG-1.5%, LFG-2%, LFG-2.5%, LFG-3%, LFG-3.5%, and LFG-4%. Except for the final concentration of flaxseed gum, all other components in these gel systems had the same final concentration; specifically, the final concentration of fish-derived myofibrillar protein was 20% (w / w), and the final concentration of sunflower seed oil for dissolving lycopene was 10% (w / w). Samples were heated in a 90°C water bath for 30 min, followed by cooling in an ice bath for 1 h. They were then stored at 4°C for subsequent analysis.

[0060] Lycopene embedding rate determination: 0.1g gel sample was added to 1mL DMSO and mixed evenly. Then, 2mL mixed organic phase solution (n-hexane: dichloromethane = 3:1, v / v) was added for extraction. After extraction 3 times, the extracts were combined and centrifuged at 3000r / min for 10min. The supernatant was placed in a spectrophotometer to measure the absorbance at 472nm. According to the lycopene standard curve (weigh 2.5 mg of lycopene standard, dissolve it in a small amount of dichloromethane, and add n-hexane to make up to 50 mL, this is the first stock solution (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 the first stock solution, respectively, and make up to 10 mL of each solution. Shake well to prepare standard solutions with concentrations of 0.5, 1, 2, 4, 8, and 16 μg / mL. Measure the absorbance of the standard solution at 472 nm. The standard curve is: Y (absorbance) = 0.0495 x (concentration) - 0.0077, R... 2 =0.9995), calculate the lycopene content in the gel sample.

[0061] 1.4 Determination of surface hydrophobicity

[0062] Weigh 1g of gel sample and mix with 1mL of distilled water. After vortexing and homogenizing, add 200μL of bromophenol blue solution and shake at room temperature in the dark for 10min. Then, centrifuge at 8000g for 10min at 4℃ and collect the supernatant. Measure the absorbance of the supernatant at 596nm using a spectrophotometer (SYNERGYH1 Bio Tek, USA), labeled A1. Use distilled water as a control; the measured absorbance is A0. Calculate the surface hydrophobicity using 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 and homogenized 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), and 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 h. The mixture was then centrifuged at 10,000 rpm for 10 min at 4 °C, and the supernatant was collected. The protein concentration in the supernatant was determined using the biuret method. The proportion of different chemical bonds in the gel sample was expressed as the proportion of protein dissolved by different reagents to the total protein concentration.

[0066] 1.6 FT-IR Spectroscopic Analysis

[0067] The FG gel sample was first placed at -80℃ for 24 hours, followed by freeze-drying. The dried gel sample was then ground into powder and stored in a desiccator. The gel powder was mixed with potassium bromide powder, ground, and prepared into thin sections for FT-IR detection. The FT-IR spectral range was 4000-400 cm⁻¹. -1 The resolution is 4cm. -1 An average of 32 scans were performed in total.

[0068] 1.7 LF-NMR Analysis

[0069] The moisture distribution and proton density of the gel samples were analyzed using LF-NMR (Suzhou Newmax Analytical Instruments Co., Ltd., Suzhou, China). 4g of gel sample was weighed and equilibrated to room temperature before being placed in an NMR tube for measurement. SR-CPMG sequence: 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 reversal times = 20, NS = 8.

[0070] The proton density of the gel was observed using magnetic resonance imaging (MRI). Uniform pseudo-colorization was performed using NMR image processing software version 3.0 (Suzhou Newmark Analytical Instruments Co., Ltd., Suzhou, China) to convert the obtained grayscale images into proton density-weighted color images (T2).

[0071] 1.8 Rheological properties

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

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

[0074] Amplitude scanning: The sample was scanned at a constant frequency of 1 Hz at 25℃ for strains ranging from 0.1% to 100%. Large amplitude oscillatory shear was scanned at a constant frequency of 1 Hz at 25℃ for strains ranging from 0.1% to 500%, and data at 1%, 10%, 100%, and 500% strain were collected to create Lissajous plots.

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

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

[0077] Three-stage thixotropic test (three-interval shear recovery test, 3ITT): at 1s -1 Sheared at a low shear rate for 180 s, followed by 100 s. -1 Shearing was performed continuously at a high shear rate for 90 seconds, and then further sheared for 1 second. -1 Shearing at a low shear rate for 270 s.

[0078] 1.9 Laser Confocal Microscopy (CLSM) Analysis

[0079] The microstructure of the emulsion gel was observed using laser confocal microscopy, and the distribution of proteins and oil droplets within the gel was imaged and analyzed. Polysaccharides (flaxseed gum), fish-derived myofibril proteins, and the oil phase (sunflower seed oil) were stained with fluorescent dyes (Calcofluor White Strain 100 μL, Nile Blue ethanol solution 100 μL, Nile Red isopropanol solution 100 μL). 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 Swallowing Foods (IDDSI)

[0081] The LFG gel was used to test and classify swallowing difficulties in accordance with the methods of the International Swallowing Disorders Standardization Initiative.

[0082] Fork drip test: Lift the gel sample with a smooth fork and observe its stacking 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 state of the sample sliding down and the state of the spoon surface after the sample slides down.

[0084] Fork compression test: Cut a gel sample of appropriate size, apply pressure to the sample surface using a fork, and observe the degree to which the sample retains its shape. Based on the IDDSI standard description, classify the gel sample deformation and particle size into textural grades.

[0085] 1.11 3D Printing Performance

[0086] The lycopene-loaded gel sample was loaded into a syringe connected to a 3D foodprinter (Hangzhou Shiyin Food Robotics Technology Co., Ltd., China), and the printing temperature was maintained at 25℃ for 1 hour to equilibrate. 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] The dynamic human gastrointestinal in vitro digestion device (Dynamic Human Gastrointestinal IV, DHSI-IV, Xiaodong ProHealth (Suzhou) Instrument Co., Ltd., Suzhou, China) was used to simulate gel digestion in the gastrointestinal tract of elderly patients. The preparation of simulated saliva (SSF), simulated gastric juice (SGF), and simulated gastric juice (SIF), as well as relevant parameters of gastrointestinal digestion in the elderly patients, and the relevant components and concentrations of SSF, SGF, and SIF are detailed in Table 1. Subsequently, pepsin was added to SGF to achieve a final pepsin enzyme activity of 3000 U / mL; pancreatin and bile salts were added to SIF to achieve a final pancreatin enzyme activity of 250 U / mL and a final bile salt concentration of 10 mM.

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

[0090] 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℃. The stomach rolling speed was 2 r / min, the pylorus opened 0-15 mm, the stomach compression was 1 mm / s, and the compression depth was 20 mm. First, 100 g of sample was mixed with 100 ml of LSF for 2 min and stirred homogenized to simulate oral feeding. Then, the sample mixture was 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 min and 180 min, 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 minutes.

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

[0094] y(t)=1-(1-e -kt ) β ;

[0095] In the formula, y(t) is the gastric contents residue ratio at time t(min); k is the gastric emptying rate per minute (1 / min); and β is the intercept of the fitted curve on the y-axis.

[0096] t 1 / 2 It is an important indicator for measuring 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] In the formula, k is the gastric emptying rate of food per minute (1 / min); β is the intercept of the fitted curve on the y-axis.

[0099] 1.13. Lycopene release behavior and bioavailability

[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 (a) Gastrointestinal digestion samples were collected at 60, 90, 120, 150, and 180 min to simulate dynamic gastrointestinal digestion. The lycopene content determination method in step "1.3" was used to analyze the lycopene release rate of the gel samples during simulated dynamic gastric and gastrointestinal digestion. The lycopene release mechanism of the gel samples was investigated by fitting the lycopene release data during the gastrointestinal digestion stage to the zero-order, first-order, and Higuchi kinetic equations.

[0101] Zeroth 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 ∞ The expression represents the cumulative release fraction of lycopene at time t, while k represents the release rate. Different equations correspond to different transport mechanisms.

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

[0106]

[0107] In the formula, C 胶束部分 and C 消化液 The concentrations of lycopene were found in the micelle fraction and the digestive fluid, respectively.

[0108] 1.14 Data Analysis

[0109] All experiments were repeated three times. Statistical significance analysis of the results was performed using SPSS software (Version 22.0, SPSS Inc., Chicago, IL, USA).

[0110] 2. Results and Discussion

[0111] 2.1 Structural characteristics of flaxseed-protein gel

[0112] Surface hydrophobicity is commonly used to characterize the degree of exposure of hydrophobic groups within proteins and plays a crucial role in determining protein functional properties. When flaxseed gum interacts with myofibrillar proteins (FG gel), it triggers a restructuring of the protein molecular structure, and changes in surface hydrophobicity become an important characterization of this restructuring process. Figure 1 As observed in Figure a, the surface hydrophobicity of the flaxseed gum-added group was significantly reduced compared to the unadded group (FG-0%). This phenomenon is attributed to the fact that the flaxseed gum polysaccharide chains form a barrier on the surface of myofibrillar protein molecules through steric hindrance, restricting the contact of surface hydrophobic groups, such as phenylalanine and leucine side chains, with the external environment. The exposure of these hydrophobic groups is inhibited, thus reducing the surface hydrophobicity of the gel. Furthermore, during the formation of the three-dimensional gel network structure, flaxseed gum and myofibrillar protein intertwine, altering the size and shape of the network pores. Hydrophobic regions that might otherwise be exposed on the surface are confined within the network, making contact with the external environment difficult, which also contributes to the reduction in surface hydrophobicity.

[0113] FT-IR is an important technique for analyzing molecular group interactions and can reveal the characteristic patterns of how flaxseed gum influences the evolution of myofibrillar protein secondary structure. For example... Figure 1 As shown in b, the gel sample is at 4000-400 cm⁻¹. -1 Six characteristic absorption peaks were observed within the range. Compared to the FG-0% group, no new absorption peaks appeared in the spectra of other gel samples, indicating that myofibrillar proteins and flaxseed gum did not form new covalent bonds. At 2930 cm⁻¹ -1 and 2860cm -1 The two peaks at 1750 cm⁻¹ originate from the stretching vibrations of aliphatic CH groups (CH₂ and CH₃ groups), reflecting the exposure and rearrangement of hydrophobic regions of myofibril proteins. -1 The absorption peak corresponds to the characteristic vibration of the C=O group of the ester carbonyl group; 1470 cm⁻¹ -1 The absorption peak is attributed to the bending vibration mode of CH2 / CH3, primarily originating from the aliphatic structure of proteins or flaxseed gum. Additionally, the 1170 cm⁻¹ peak... -1The characteristic peaks at this location are closely related to the stretching vibrations of COC glycosidic bonds. To infer changes in protein secondary structure, Fourier deconvolution combined with second derivative spectroscopy was used to analyze the FG gel amide I band (1600-1700 cm⁻¹). -1 The conformational features of ) are analyzed. Figure 1 (ci). 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%, when FG addition is between 1.5wt% and 3wt%, the α-helix content of the gel decreases, while the β-sheet ratio increases, indicating the unfolding of protein structures and enhanced intermolecular interactions. Flaxseed gum can promote the formation of β-sheets, causing protein structures to unwind and creating conditions for protein cross-linking, ultimately forming a stable three-dimensional gel matrix. However, the α-helix content in the FG-3.5% gel system is higher than that in the FG-0% group, while the β-sheet content is lower. This may be because high-concentration flaxseed gum induces an increase in α-helices through electrostatic shielding, promoting cross-linking between proteins and flaxseed gum, making the protein sequences within the gel system more ordered. Previous studies have shown that the β-sheet content in heat-induced protein gels is considered positively correlated with their hardness; therefore, the decrease in β-sheet content in the FG-3.5% gel system suggests that its texture may be more suitable for people with swallowing difficulties. 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 characteristics, with their apparent viscosity negatively correlated with the shear rate. Figure 2(g) In the FG-0% gel system, rod-shaped myosin or inflated fragments in the myofibrillar protein (MP) typically overlap and entangle, and their steric hindrance and intermolecular friction increase the viscosity of the system. The apparent viscosity of the FG-1.5% and FG-2% gel systems is higher than that of the FG-0% gel system, mainly due to the synergistic thickening effect induced by the entanglement of flaxseed gum and myofibrillar protein molecules. When the flaxseed gum content increases to 2.5 wt%, its steric occupancy effect significantly interferes with the self-assembly of myofibrillar proteins, disrupting the ordered connections between proteins, leading to the breakage of the three-dimensional network structure and resulting in the lowest viscosity. As the flaxseed gum content increases to 3 wt%-4 wt%, flaxseed gum and myofibrillar proteins reconstruct the gel network structure 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 interprotein chains, ultimately increasing the viscosity of the FG gel system. When 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 3D extrusion molding, thereby improving printing accuracy and molding stability.

[0116] Multidimensional rheological characterization revealed that the amount of flaxseed gum added had a significant structure-activity relationship on the viscoelasticity of fish-derived myofibril proteins. Amplitude scanning analysis showed that ( Figure 2 In the strain range of 0.1-1%, all FG gel systems maintained linear viscoelastic responses in terms of G' and G” values, indicating relatively stable network structures. Within the linear viscoelastic region, all FG gel samples exhibited a characteristic where G' was greater than G”, suggesting that they primarily exhibited elastic-dominated semi-solid gel behavior. When the strain exceeded the critical value, the high-concentration flaxseed gum groups (FG-3%, FG-3.5%, and FG-4%) exhibited characteristic Type III nonlinear viscoelastic behavior, characterized by a decrease in G', while G” showed a dynamic evolution of first increasing and then decreasing in the nonlinear viscoelastic region. The decrease in G' and G” also reflects the disruption of intermolecular interactions and network structure rupture in the gel samples at this strain. Furthermore, when the strain exceeded the linear viscoelastic region, tanδ showed a geometric increase, demonstrating the gradual strengthening of the viscous dissipation mechanism during the network disintegration of the gel samples. At high strain amplitudes, the tanδ of the gel system with added flaxseed gum is higher than that of the FG-0% gel system, indicating that the addition of flaxseed gum can enhance the flow properties of the gel sample under high stress and reduce swallowing resistance.

[0117] Frequency scanning results showed that as the amount of flaxseed gum added increased, both G' and G” of the FG gel system decreased, but the FG gel system consistently maintained a solid-like characteristic where G' was greater than G”. Figure 2(d and e in the text). This indicates that flaxseed 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 physical crosslinking and entanglement, which allows the network to store more energy during rapid deformation, and also reflects the network structure's greater sensitivity to changes in reaction rate. Throughout the frequency scan range, the tanδ of all gel systems is below 0.5, indicating that the gel system is predominantly elastic. Figure 2 (f) As shown in the figure, when the amount of flaxseed gum added is ≥2.5wt%, the tanδ of the gel system decreases with increasing frequency. At low shear frequencies, a higher tanδ value is beneficial for the gel system to form a cohesive bolus in the oral cavity, reducing oral residue. The decrease in tanδ at high shear frequencies indicates that the gel system has enhanced elasticity and resistance to fragmentation during rapid deformation, which is beneficial for the bolus to maintain its integrity during swallowing, reducing the risk of fragmentation and pharyngeal residue.

[0118] Creep and recovery behavior characterize the deformation resistance and energy dissipation mechanism of gel samples under external forces. Generally, when the gel network structure is more compact, its pore size is smaller and more uniformly distributed. In this case, if an external force is applied to the network structure, the network tends to become more stable, making segment migration and molecular chain displacement more difficult. This restricted displacement increases internal friction within the gel, thus enhancing its resistance to deformation. Figure 2 As shown in h, all gel samples exhibited similar creep recovery characteristics, undergoing transient deformation during stress loading and unloading, and all gel samples showed irreversible strain. Within 0-180 s, when the gel samples were subjected to constant stress, their deformation increased over time. Compared to the FG-0% gel system, the addition of flaxseed gum increased the degree of deformation in the gel system. The FG-3% gel system showed the greatest deformation, which corresponds to its lowest G' in the linear viscoelastic region, indicating its weaker elastic properties. Between 180-360 s, after removing the stress from the gel system, the deformation decreased over time, reaching a certain value and then stabilizing, indicating that the gel system exhibited viscous flow characteristics, but some deformation remained irreversible. Flaxseed gum increased the degree of deformation and showed good deformation recovery, indicating that the gel system could easily undergo moderate deformation under tongue pressure to pass through the narrow pharyngeal region, while the good deformation recovery characteristics effectively inhibited excessive deformation and disintegration of the food bolus, ensuring its structural integrity during esophageal transport.

[0119] from Figure 2 As can be seen in Figure i, the viscosity differences among the gel samples were relatively small in the first stage, with the viscosity of the gel system with added flaxseed gum being slightly lower than that of the FG-0% gel system. In the second stage, under high shear rates (100 s⁻¹), the viscosity of the gel system increased. -1The structure of the gel system is disrupted, and the viscosity decreases significantly. This is because the high shear force destroys the three-dimensional network structure of the gel system, weakening the intermolecular forces and leading to a decrease in viscosity. When the shear rate recovers to 1 s⁻¹, the viscosity decreases. -1 At this stage, the viscosity of the FG gel system recovers. Specifically, the FG-0%, FG-1.5%, and FG-2% gel systems exhibit higher viscosities in the third stage than in the first stage, indicating strong structural recovery and thixotropy. This helps improve the accuracy of 3D printing, increasing the resolution and quality of printed products. However, for individuals with swallowing difficulties, this can slow food movement through the esophagus, significantly prolonging the swallowing process and potentially causing discomfort and increasing the risk of choking. While the FG-2.5%, FG-3%, FG-3.5%, and FG-4% gel systems show slightly lower viscosities in the third stage than in the first stage, they still possess good structural recovery capabilities, maintaining the shape and structure of the 3D printed product.

[0120] 2.3 Microstructure of flaxseed-protein gel

[0121] Observation using laser confocal microscopy Figure 2 The image (j) provides a direct visual analysis of the microstructure and droplet distribution of the FG gel system. Blue, green, and red fluorescent signals correspond to the spatial distribution of flaxseed gum, the oil phase, and the myofibrillar protein components, respectively. In the FG-0% gel system, the oil droplets are irregularly shaped, relatively large, and loosely distributed within the gel network. The large, non-uniform oil droplets indicate a lack of effective emulsification or stabilization mechanisms in the FG-0% gel system, making it difficult to uniformly disperse the oil phase into small droplets. The loose distribution of oil droplets within the gel network suggests poor binding capacity of the gel network to the oil phase, preventing the formation of a tightly ordered microstructure. This may lead to poor stability of the entire gel system, making it prone to breakage during swallowing and increasing the risk of choking. After introducing flaxseed gum, the oil droplet size in the gel system significantly decreased, and the spatial arrangement became more compact. This structural change 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 and spatial repulsive forces between oil droplets, thereby altering their distribution. Simultaneously, the continuity and density of the gel network provide a rigid confinement space for the oil droplets. This not only effectively improves the encapsulation efficiency of functional factors but also endows the 3D printing material with excellent structural fidelity. Furthermore, the synergistic effect of uniform oil droplet distribution and enhanced interfacial adsorption ensures rapid deformation of the bolus under low shear triggering during swallowing. At the same time, maintaining a suitable elastic modulus prevents premature structural disintegration, making the gel system suitable for the physiological and mechanical requirements of individuals with swallowing disorders.

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

[0123] By regulating the molecular structure of flaxseed gum, the network properties and physicochemical properties of myofibrillar protein gel were significantly enhanced, demonstrating its potential for dual-function applications in bolus construction for dysphagia and food 3D printing. To further improve the nutritional properties of the swallowing-adaptive gel, this invention constructed a nutritionally fortified composite system—a lycopene-loaded flaxseed gum-MP gel system (LFG gel system)—using a lycopene-loading strategy. Since the LFG-0% gel system without added flaxseed gum cannot effectively encapsulate lycopene, results for the LFG-0% gel system are not presented. Figure 3 As shown in Figure a, with the increase of flaxseed gum addition, the encapsulation efficiency of lycopene showed an overall upward trend, clearly indicating that flaxseed gum plays a positive and crucial role in the encapsulation process of lycopene. The addition of flaxseed gum can induce an enhanced polysaccharide-protein interaction effect, constructing a more stable gel network, thereby providing more space and sites for encapsulating lycopene and improving the encapsulation efficiency. In the low concentration stage (1.5wt%-2wt%), flaxseed gum initially cross-links with myofibrillar proteins to form a basic network framework. However, due to the weak intermolecular interactions, the gel network density is poor. This weak interaction and loose network structure limit the gel's ability to encapsulate lycopene. Therefore, the lycopene encapsulation efficiency (encapsulation efficiency) only increased from 73.10% to 74.79%, an increase of 3.24%. The encapsulation efficiency of the LFG-2.5% gel system decreased abnormally, with the lowest lycopene encapsulation efficiency (72.37%). It is speculated that at this concentration, micro-phase separation occurs between flaxseed gum and protein molecules. This phenomenon disrupts the uniformity and continuity of the gel network, weakening the binding capacity of the gel matrix for lycopene. However, in the high concentration region (3wt%-4wt%), the hydrogen bonding interactions between gel system molecules are enhanced, forming a more compact three-dimensional network structure. This dense three-dimensional network achieves a synergistic immobilization effect on lycopene by enhancing steric hindrance and interfacial affinity. Under these conditions, the lycopene encapsulation efficiency can reach up to 85.99%, demonstrating excellent encapsulation performance.

[0124] 2.5 Intermolecular interactions of flaxseed-protein gel loaded with lycopene

[0125] The intermolecular forces in the LFG gel system exhibit nonlinear kinetic characteristics as the flaxseed gum concentration changes. Figure 3As shown in b, 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. In the low concentration range (1.5 wt%-2 wt%), the ionic bond content increases with increasing flaxseed gum content. This indicates that the appropriate introduction of flaxseed gum provides more charged groups, promoting ionic bond formation. However, when the FLG addition increases to 2.5 wt%, the ionic bond content in the gel system decreases by 40.16%. Conversely, hydrogen bonding and hydrophobic interactions increase by 72.14% and 35.53%, respectively. This change may be because this concentration of flaxseed gum disrupts the original electrostatic balance of the LFG gel system, inhibiting ionic bond formation. Simultaneously, flaxseed gum promotes structural rearrangement of fish-derived myofibril proteins, making it easier for intermolecular polar groups to form hydrogen bonds, thereby enhancing hydrogen bonding. Furthermore, the altered distribution of hydrophobic regions in the gel system also contributes to the enhancement of hydrophobic interactions. With further increases in flaxseed gum content (3wt%-4wt%), the hydrogen bond network continued to strengthen. This may be because the densification of polysaccharide chains induces an interfacial water rearrangement effect, increasing the contact probability between polar groups connected by water bridges. However, hydrophobic interactions showed a decreasing trend, presumably due to the spatial shielding effect of the flaxseed gum polysaccharide chains, reducing the accessibility of hydrophobic groups. Furthermore, the disulfide bond content in the LFG gel system fluctuated, possibly related to conformational changes in protein molecules caused by variations in flaxseed gum concentration and changes in the redox environment within the gel system. When the flaxseed gum content increased to 2.5wt%, the disulfide bond content rose from 13.24% (LFG-2% gel system) to 20.09%. This may be because the protein conformational unfolding in the LFG-2.5% gel system exposed more thiol groups, thereby achieving network structure reconstruction. However, after densification in the LEF gel system with high flaxseed gum content, disulfide bonds were gradually replaced by hydrogen bonds and other bonds.

[0126] 2.6 Moisture State and Distribution

[0127] LF-NMR often analyzes the migration rate of water molecules in gels by measuring the T2 relaxation time. The T2 relaxation time distribution curve of the gel is shown below. Figure 3 As shown in c in the figure. The figure shows that each sample has three peaks, which, in order of relaxation time, characterize three different types of moisture, namely T... 21 (bound water), T 22 (immobilized water) and T 23 (Free water). With increasing flaxseed gum content, the T2 peak of the LFG gel system shifts to lower relaxation times, indicating a decrease in water molecule mobility. This phenomenon stems from the increased protein cross-linking density induced by flaxseed gum, leading to the construction of a dense network structure. In the LFG-3.5% gel system, T... 21The value was the lowest, and the peak area ratio was higher than other groups. This indicates that at this concentration, the three-dimensional network forms a strong binding effect on water molecules through polar groups. That is, the interaction between flaxseed gum and fish-derived myofibril protein has a significant impact on bound water, effectively binding water molecules at specific locations. 22 The amount of flaxseed gum added decreases as the amount of flaxseed gum increases. This phenomenon confirms that flaxseed gum can promote the tight trapping of water molecules in the gel system and limit their migration. 22 The decrease in T is mainly attributed to the increasingly stronger non-covalent interaction between flaxseed gum and water molecules, which restricts the rotation, translation, and other movements of water molecules. 23 The largest peak area ratio indicates that the water in the gel system exists primarily as free water. As the amount of flaxseed gum added increases, the Tg, representing free water, increases. 23 The peak area shows a decreasing trend, which may be due to the interaction between water molecules and the hydrophilic groups of proteins 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 a gel, making it an effective visualization method for studying the water distribution in protein gels. Differences in the size and distribution of red spots in a pseudocolor image can reflect differences in the distribution of water molecules within the gel. Figure 3 (di in the image). The red areas in the image represent strong resonance signals and high hydrogen proton density, which are positively correlated with the water content embedded in the gel system. The red areas in the FG-3.5% gel system show uniformly distributed honeycomb-like signal patches, presumably related to the more compact and ordered network structure. This indicates that at this concentration, the optimization of the gel system structure by flaxseed gum not only affects the water migration rate but also makes the water distribution in the gel more uniform, which has positive implications for the application of the gel system in foods for dysphagia and 3D printed foods.

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

[0130] Rheological properties play a crucial role in regulating the extrusion flowability and structural stability of food 3D printing inks. Ideal inks should possess shear-dilution properties, maintain a moderate elastic modulus to enhance self-supporting properties, have a moderate apparent viscosity to reduce friction with the nozzle, and have a moderate creep recovery rate to ensure that apparent viscosity and modulus recover rapidly after extrusion. Figure 4The value of 'a' in the figure indicates that G' is higher than G'" in all LFG gel systems within the linear viscoelastic region, suggesting that the lycopene-loaded flaxseed-protein gel system still exhibits elasticity-dominated gel properties. This property allows 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 both G' and G'", indicating that the structure of the gel system will be damaged under large strains, and its viscoelasticity will also change. Figure 4 Figures b and c show the Lissajous curves of LFG gel systems prepared with different concentrations of FG, a method for visually revealing nonlinear viscoelastic properties. At low strain amplitudes, the elastic Lissajous curves of the LFG gel system exhibit 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 shifts from elastic dominance to plastic behavior. This means that the mechanical behavior of the gel changes under different strain conditions; its plastic deformation capacity increases at high strain, which may affect the accuracy and shape retention of 3D printing. Figure 4 The viscosity lissajous curve of LFG gel gradually changes from elliptical to spindle-shaped, indicating that the LFG gel exhibits shear-thinning behavior. This shear-thinning property is beneficial for smooth ink extrusion during 3D printing. During extrusion, the gel is subjected to shear force, reducing viscosity and allowing it to pass smoothly through the nozzle, minimizing friction. At a strain of 500%, a secondary loop appears in the viscosity lissajous curve. This is due to microstructural rearrangement leading to the emergence of a new network structure, indicating that the addition of flaxseed gum contributes to the stability of the LFG gel system's microstructure at higher strains.

[0131] In the frequency range of 0.1-100 Hz, all LFG gel systems exhibited weak frequency dependence, and their G' values ​​were all greater than G', indicating that all LFG gel systems exhibited 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 is in the range of 1.5wt%-3wt%, the mechanical strength of the gel system is [not specified]. This is likely due to the enhanced interactions between flaxseed gum and proteins, as well as between proteins themselves, promoting the formation of a stronger and tighter intermolecular network structure, thus improving the mechanical strength of the gel system. This increased mechanical strength is beneficial for improving the printability of the gel, allowing it to better maintain 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 because excessive flaxseed gum impairs the interactions between proteins. Because too many flaxseed gum molecules interfere with the normal interactions between protein molecules, the originally formed stable intermolecular network structure is destroyed, thus reducing the mechanical strength of the gel system. It is noteworthy that the G' and G'" of the LFG-1.5% gel system are significantly lower than those of other groups. The higher G' and G'" of other groups are mainly attributed to the interactions between protein-FG and protein-protein molecules. This interaction promotes the formation of a stronger and denser intermolecular network structure in the gel system. When tanδ is higher than 1, the gel system exhibits greater viscosity, while when tanδ is lower than 1, it exhibits more solid-like properties. Except for the LFG-1.5% gel system, the remaining LFG gel systems have tanδ < 0.5 across the entire frequency range, showing good potential for 3D printing. This is because a lower tanδ means the gel system is more likely to exhibit solid-like properties, possessing better elasticity and structural stability, meeting the requirements of 3D printing inks, and better maintaining shape and structure during printing, thus contributing to high-quality 3D printing.

[0132] The viscosity of all LFG gel systems decreases with increasing shear rate, exhibiting shear thinning, and thus classifying them as pseudoplastic fluids. Figure 5 (b) Shear thinning can be attributed to the increased shear rate disrupting aggregated particles, weakening interparticle interactions, and thus reducing apparent viscosity. The shear thinning behavior exhibited by the LFG gel system has already had a positive impact on patients with dysphagia. During swallowing, food is subjected to shear forces in the oral cavity and pharynx. Due to the shear thinning properties of the LFG gel system, its viscosity decreases and its fluidity increases under shear forces, making it easier to swallow. This helps reduce resistance during eating in patients with dysphagia, reduces the risk of aspiration, and improves the safety and smoothness of swallowing. At low shear frequencies (0.1-10 s...), the shear thinning effect is observed. -1Within the range of 1.5wt%-3wt% flaxseed gum addition, the viscosity of the LFG gel system increased with increasing FG content. This is likely because flaxseed gum increases the viscosity of the continuous phase, while simultaneously increasing the number and aggregation of particles encapsulating between droplets in the gel system, thus hindering droplet movement. However, when the FG content increased to 4wt%, the viscosity of the LFG gel system decreased. This may be because when the FG content exceeds a certain value, it cannot further enhance the structure of the gel system, and flaxseed gum itself has a strong gelling effect. Therefore, at higher flaxseed gum content, the gelling effect of the LFG gel system is dominated by flaxseed gum.

[0133] Creep testing can identify the cross-linking characteristics within a gel system over a longer timescale. 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 showed similar creep curves, reflecting typical viscoelastic fluid characteristics. The LFG-3% gel system had the lowest maximum creep value, indicating that the gel network has strong cohesion and good deformation resistance. After stress removal, due to irreversible strain, some deformation could not be fully recovered. For 3D printing inks, high elasticity and strong strain resistance are beneficial for subsequent layer deposition and reducing damage during printing. However, excessively high strain resistance is not friendly to people with swallowing disorders, significantly increasing their risk of choking. Therefore, 3D printed food for people with swallowing disorders needs to find a balance between meeting the high elasticity and strain resistance requirements of 3D printing and ensuring safe consumption by people with swallowing disorders.

[0134] The three-stage thixotropic test reflects the ability of different gel samples to recover their structure after shearing, which can indicate the potential of different gel samples as 3D printing bio-inks. Figure 5 d in the figure shows all gel samples at different shear rates (low 1s). -1 High speed 100s -1 and lower 1s -1The viscosity changes were observed. In the first stage, the LFG gel system exhibited high viscosity, with the viscosity values ​​of the LFG gel systems with FG additions ranging from 2.5 wt% to 4 wt% remaining relatively stable. As the shear rate of all gel samples increased from low to high, the viscosity decreased significantly due to the shear thinning effect. This was simulated momentarily when the gel system passed through the 3D printing nozzle. However, as the shear rate decreased from high to low, the viscosity recovered rapidly, indicating that the gel system regained sufficient mechanical strength after passing through the nozzle to support subsequent multilayer loads. Except for the LFG-1.5% gel system, the final viscosity of the other gel systems after shearing was slightly lower than the initial value. This may be because the strong shear force disrupted the network structure of the gel system, and the reconstruction of the gel system requires high energy and time, making it difficult to restore the initial viscosity.

[0135] 2.8 Results of Laser Confocal Microscopy (CLSM) Analysis

[0136] Differences in the microstructure of a gel system can affect its rheological properties, encapsulation and release capabilities of active substances, etc. From the CLSM images of the LFG gel system (… Figure 5 As shown in e), the gel network becomes denser with increasing flaxseed gum content, indicating that the interaction between flaxseed gum and fish-derived myofibrillar proteins strengthens with increasing flaxseed gum content. The chemical bonds (such as hydrogen bonds and ionic bonds) formed between flaxseed gum and the myofibrillar proteins in the gel system promote the gradual densification of the gel network. A denser network structure results in better stability and lycopene encapsulation capacity of the gel system. Increased flaxseed gum content also leads to smaller and more uniform oil droplet size. Uniform oil droplet distribution helps improve the rheological properties of the LFG gel system, contributing to improved texture and mouthfeel in foods with swallowing difficulties and reducing the risk of aspiration. Furthermore, for 3D printed food, a uniform structure is beneficial for the stability of the printing process and the quality of the printed product.

[0137] 2.9 Results of the International Standard for Swallowing Food Grading and Testing (IDDSI)

[0138] IDDSI provides a globally standardized testing method for evaluating foods designed for patients with dysphagia. Therefore, fork dripping tests, spoon tilting tests, and fork squeezing tests were performed to assess the potential of the LFG gel system as a food for patients with dysphagia. Figure 6The fork-drop test results in section a showed that the LFG gel systems all maintained their shape on the fork. Specifically, the LFG-1.5% gel system aggregated into larger droplets at the fork tip but did not fall off, exhibiting a pudding-like consistency. Highly thickened fluids or pudding-like foods minimize food flow during swallowing, improving swallowing safety. The spoon tilt test on the fork can be used to assess the viscoelasticity of the samples. As shown in the figure, the LFG-1.5% and LFG-2.5% gel systems retained more residue on the spoon during tilting. While these two gel systems maintained their shape on the spoon, the greater residue retained during tilting and gentle shaking indicates their high viscosity, making them unsuitable as a diet for patients with dysphagia. This is because highly viscous foods increase the risk of choking in patients with dysphagia. The LFG-2%, LFG-3%, LFG-3.5%, and LFG-4% gel systems maintained their shape on a spoon and easily slid off the spoon when tilted and gently shaken, leaving almost no sample residue. This indicates that these four gels are easy to swallow and do not stick to the tongue or throat. In the fork crushing test, the LFG-3% and LFG-3.5% gel systems were easily crushed by a fork (the pressure was insufficient to cause the fingernail to turn white), and their shape remained unchanged and the pattern was still visible after the fork was removed. Therefore, these two gels were classified as Level 5 chopped moist food, requiring only slight chewing and no biting. The LFG-4% gel system, however, required pressure that caused the fingernail to turn white before deforming and did not immediately return to its original shape after the pressure was removed. Therefore, it was classified as a Level 6 easily swallowable food. In conclusion, the addition of flaxseed gum effectively improves the texture characteristics of LFG gel systems, making them suitable for people with swallowing difficulties.

[0139] 2.10 3D Printing

[0140] Printability and shape stability are important aspects of food 3D printing performance, providing crucial standards for evaluating the printing effects of different gels. Indicators such as distinct layers, clear textures, and strong printability are essential for measuring the quality of 3D printed products, directly impacting their appearance and usability. Figure 6Figure b shows the 3D printing effects of LFG gels prepared with different concentrations of flaxseed gum. The LFG-1.5% gel system had too low a glycemic index (G') and viscosity, resulting in excessive ink being extruded from the nozzle during printing. Furthermore, the ink could not quickly return to its solid state after depositing on the platform, leading to product collapse and poor printing performance. This indicates that appropriate G' and viscosity are fundamental to successful 3D printing; excessively low G' and viscosity make it difficult to control or shape the gel ink during printing. Other gel samples flowed smoothly and continuously from the nozzle during 3D printing, exhibiting good deposition properties. However, the printing quality of LFG gel systems with different concentrations of flaxseed gum varied. The LFG-2% gel system produced petal shape retention poorly, with partial collapse and unclear texture, indicating insufficient shape stability at this concentration. With increasing flaxseed gum content, the petal shape retention improved, with clearer lines and surface textures. Among the inks, the LFG-3.5% gel system performed best, maintaining its shape well, without collapsing, and exhibiting clear textures. This indicates that increasing the flaxseed gum concentration positively impacts the viscoelasticity of the LFG gel system ink. Higher viscoelasticity allows the gel ink to better maintain its shape during printing, reducing deformation and collapse, thus resulting in superior printing performance. Compared to paste-like or mushy foods, the 3D-printed LFG-3.5% gel system has an appealing appearance, which is particularly significant for patients with dysphagia. A pleasant appearance may increase patients' appetite, enhance their enjoyment of eating such foods, and contribute to a better dietary experience, potentially having a positive impact on their nutritional intake and mental health. This also demonstrates the advantage of 3D printing technology in preparing foods for dysphagia, namely, meeting the specific needs of patients through personalized design.

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

[0142] pH changes of gel samples during dynamic gastric digestion, as shown in the following figures. Figure 7As shown in a. Before adding the gel sample, the pH of the simulated fasting gastric juice was 3, simulating the fasting state of the elderly. In the initial stage (0-20 min), the pH of the gastric contents of different LFG gel systems significantly increased from the fasting value of 3.0 to 6.28-6.58. This is due to the buffering effect produced by the gel system after entering the gastric cavity from the esophagus via the oral cavity and the consumption of gastric acid during gel decomposition. With the extension of dynamic gastric digestion time, the gastric pH value showed a decreasing trend. This is related to the continuous secretion of simulated gastric juice and hydrochloric acid and the reduced buffering capacity of the gel sample due to the gastric emptying process during digestion. At 40 min of dynamic gastric digestion, the pH of the FG-1.5% gel system, FG-2% gel system, and FG-2.5% gel system was relatively low, which may be due to the low stability of ionic bonds and disulfide bonds in the gel structure under gastric acid environment. At 100-120 min of dynamic gastric digestion, the pH of the other gel systems, except for the LFG-3% gel system, increased slightly. This may be because as digestion progresses, some components of the gel are gradually digested or broken down, and their buffering effect on gastric acid or other factors affecting acid balance change.

[0143] During gastric digestion, the gel undergoes disintegration and dissolution through peristalsis and is emptied into the duodenum. The gastric emptying characteristics of the gel system during dynamic gastric digestion mainly depend on the gel's structural properties, such as size, texture, viscosity, and microstructure. Generally, large and dense food particles take longer to shrink in the gastric antrum, thus requiring a longer emptying time. Soft food particles empty significantly faster than hard food particles. Gastric emptying curves simulating the dynamic gastric digestion process in elderly individuals show that the gastric retention rate gradually decreases with increasing digestion time. Figure 7 (b) After 120 min of dynamic gastric digestion, the LFG-4% gel system exhibited the highest gastric retention rate, presumably due to the flaxseed gum-dominated gel structure inhibiting gastric emptying. This suggests that a high flaxseed gum content leads to a denser gel structure, hindering the arrangement of the gel system within the stomach. The correlation coefficients (R²) between different gel samples and the Elashoff model fitting were also discussed. 2 The higher β value indicates that the model can fit the gastric emptying process of the gel well. According to the Elashoff model fitting results (Table 2), the LFG-1.5% gel system, LFG-2% gel system, and LFG-4% gel system have β>1, indicating delayed gastric emptying, and their gastric retention rate at 20 min of dynamic gastric digestion is higher than other groups. This suggests that the structural characteristics of these three gels require a longer time 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 the solid food. The LFG-3.5% gel system has the highest gastric emptying rate constant (k), and t... 1 / 2The lowest value indicates that the gel system has rapid emptying properties. This is beneficial for the digestion of the elderly, as rapid emptying can reduce the burden on the stomach and avoid indigestion caused by food staying 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 in the stomach and passage through the pylorus, and its texture, viscosity, and other structural characteristics may be more suitable for the gastric digestive function of the elderly.

[0144] Table 2. Fitting results of the Elashoff model

[0145] 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 Image c shows images of gastric digestate from gel samples collected at different times during dynamic simulated digestion. The gastric digestate appears a dark orange color because the gel sample structure is disrupted during digestion, releasing lycopene which disperses throughout the gastric contents. As digestion time increases, the color of the digestate gradually lightens. This is due to the emptying of the stomach and the continuous secretion of gastric juices, which dilutes the lycopene in the chyme, resulting in a lighter color. This phenomenon directly reflects the changes in the composition of the gastric contents during digestion. The microscopic structure diagram shows that as the dynamic gastric digestion time increases, the particle size in the chyme decreases, the oil droplet distribution becomes more uniform, and the content of contents also decreases relatively. Figure 7 (d) This indicates that under the digestive action of the stomach, the gel structure is gradually disrupted, the particles are refined, and the oil droplets are redistributed. This further illustrates the influence of the gastric digestion process on the gel microstructure, making it gradually more uniform and smaller, consistent with the general law of food decomposition and refinement during digestion. Compared with the gastric dynamic digestate of the gel, the particle size and number of particles in the digestate after gastrointestinal dynamic digestion are significantly reduced. This indicates that after further digestion in the small intestine, food is more thoroughly decomposed and absorbed, reflecting the gradual processing and transformation of the gel system throughout the digestive process, and also suggesting the influence of the digestive functions and synergistic effects of different parts of the gastrointestinal tract on the degree of food digestion.

[0147] 2.12. Digestive characteristics of lycopene during in vitro dynamic digestion process

[0148] from Figure 8 The release curves of lycopene from the gel system during in vitro dynamic gastric and in vitro dynamic gastrointestinal digestion can be observed. As the duration of dynamic gastric digestion increases, the amount of lycopene released shows an increasing trend, which is consistent with the normal pattern of gradual release of substances during digestion. Figure 8(b) During gastric dynamic digestion, the LFG-2% gel system showed the highest lycopene release rate (30.79%) at 120 min, 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 amounts of flaxseed gum have varying effects on the encapsulation and release characteristics of lycopene. The slow release of lycopene during gastric digestion is beneficial for improving its bioavailability. Compared to gastric digestion, the gel system showed a significantly increased lycopene release after gastrointestinal digestion because the environment in the small intestine (such as bile salts) allows lycopene to form micelles, thereby promoting its absorption and utilization. During gastrointestinal dynamic digestion, the LFG-1.5% and LFG-3.5% gel systems maintained relatively high release rates of 51.17% and 49.85%, respectively, after 180 min of gastrointestinal digestion.

[0149] To investigate the release of lycopene during in vitro dynamic gastric and gastrointestinal digestion, zero-order, first-order, and Higuchi models were used to analyze the lycopene release process. The dynamic parameters of lycopene release from the gel obtained through model fitting are shown in Table 3. The data clearly show that the release curves of the gel samples are in high agreement with the applied models. During dynamic gastric digestion, except for the LFG-3.5% gel system, the release curves of other gel systems showed the highest correlation coefficients with the first-order dynamic model, indicating that lycopene release during in vitro dynamic gastric digestion is dominated by passive diffusion driven by the concentration gradient at the gel-gastric juice interface. The release curve of the LFG-3.5% gel system during gastric digestion fits the Higuchi model well, indicating that the release of lycopene in the LFG-3.5% gel system follows a swelling-diffusion mechanism. This may be related to the swelling characteristics of its gel structure in the stomach, where swelling allows lycopene to gradually diffuse out, 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. However, the release of lycopene from the LFG-3.5% gel system during dynamic gastrointestinal digestion approximates a zero-order model, implying that the release of lycopene is controllable and occurs at a constant rate. Furthermore, the release behavior of the LFG-3.5% gel system during dynamic gastrointestinal digestion depends on the gradual degradation of the gel, 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, thereby releasing lycopene at a constant rate. This characteristic has potential advantages for controlling lycopene release and improving its bioavailability.

[0150] Table 3. Correlation coefficients (R²) of lycopene in gels obtained after fitting different models. 2 )

[0151]

[0152]

[0153] from Figure 8 As shown in section d, a complex dynamic regulatory relationship exists between the amount of flaxseed gum added and the bioavailability of lycopene during dynamic gastrointestinal digestion. In the low concentration range (1.5wt%-2wt%) of LFG gel system, the bioavailability of lycopene showed an increasing trend during the 60-150 min period of gastrointestinal digestion. This indicates that the loose gel network at this concentration is conducive to the formation of mixed micelles of fatty acids and bile salts to dissolve lycopene, thereby improving the bioavailability of lycopene. However, at the end of digestion at 180 min, the bioavailability showed a decreasing trend. This is likely because the release reached its peak in the early stage, exceeding the instantaneous loading capacity of the micelles, resulting in the oxidation and loss of some unbound lycopene due to precipitation. For the LFG-2.5% gel system, its bioavailability dropped sharply to 64.67% at 120 min of digestion. This phenomenon may be due to changes in the gastrointestinal environment, causing local network collapse, exposing lycopene to the digestive environment, and thus causing degradation. The LFG-3.5% gel system maintained a relatively stable bioavailability (81.07%) throughout the gastrointestinal digestion process. This is likely due to the appropriate gel cross-linking density, which allows it to match the dynamic encapsulation capacity of micelles through a sustained-release mechanism while maintaining the network's resistance to digestive enzymes and preventing late-stage collapse. When the flaxseed gum content increased to 4 wt%, the high-density network excessively inhibited lycopene release in the initial stage, leading to concentrated lycopene release in certain time periods. Therefore, the LFG-4% gel system achieved a maximum lycopene bioavailability of 87.39% after 120 minutes of dynamic gastrointestinal digestion. However, due to the limited encapsulation efficiency of micelles for lycopene, the bioavailability decreased to 75.14% after 150 minutes of gastrointestinal digestion. In conclusion, the LFG-3.5% gel system successfully achieved a dynamic balance between network strength and micelle encapsulation rate, and its stable release pattern is more suitable for the physiological characteristics of the elderly population.

[0154] 2.13. The dynamic digestion-controlled release mechanism driven by flaxseed gum-myofibrillar protein molecular interactions

[0155] Flaxseed gum regulates the structure of myofibrillar protein gels through multi-scale 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 on these side chains provide ample 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 proteins through electrostatic interactions, disrupting the intrinsic hydrogen bond network of myofibrillar proteins and inducing a conformational shift in their secondary structure from α-helices to β-sheets. This conformational shift drives the hydrophobic core to embed into the molecule, reducing the surface hydrophobicity of the protein and thus inhibiting the disordered stacking of thermo-induced aggregates, building a stable elastic network. When the amount of flaxseed gum added is 3.5 wt%, its electrostatic shielding effect weakens the ionic bonds between fish-derived myofibrillar proteins, induces the formation of α-helices, strengthens the weighting of hydrogen bonds and hydrophobic interactions, and forms a highly viscoelastic interpenetrating network. The dynamic equilibrium between different interaction forces in the network gel system provides the molecular basis for the dynamic deformation of the food bolus during swallowing. At the mesoscale, the entanglement of the flaxseed gum backbone and oil droplets reduces the non-uniformity of oil droplet distribution and constructs a dense three-dimensional gel network through a spatial synergistic confinement effect. The dense gel network structure and the increased cross-linking density of myofibrillar proteins reduce water molecule migration, and free water in the gel system is effectively bound by the anchoring effect of hydrophilic groups. The regulation of water distribution in the LFG gel system by flaxseed gum not only prevents the texture deterioration of the food bolus due to free water leakage during swallowing, but also enhances the encapsulation capacity of lycopene. At the digestive response level, the acidic gastric digestive environment triggers carboxylation of flaxseed gum, leading to conformational contraction. This enhances the electrostatic attraction between flaxseed gum and fish-derived myofibrillar proteins, forming a dense and stable complex structure that effectively delays the release of lycopene in the stomach. During the dynamic digestion process in the gastrointestinal tract, the ionization of carboxyl groups in the neutral environment of the small intestine causes the molecular chains to extend and generate swelling pressure. The ordered network gradually relaxes, triggering lycopene to diffuse along a Higuchi pattern within the gel network, and its release rate dynamically matches the intestinal micelle embedding threshold. When the flaxseed content is 3.5 wt%, the release behavior of lycopene in the gel system has a higher fit to the zero-order equation, indicating that the release process of the LFG-3.5% gel system during gastrointestinal digestion is more gradual, mainly related to the disintegration of the gel structure, achieving a dynamic match between release kinetics and micelle embedding threshold. The cross-scale coupling of rheological properties and swallowing properties further verifies the functional adaptability of the gel. Shear thinning properties ensure low-resistance deformation under swallowing stress, while thixotropic recovery properties reshape structural rigidity during esophageal transport, achieving a dynamic balance of "compression-deformation-anti-collapse". Combining the IDSSI test results and 3D printing performance, the LFG-3.5% gel system is classified as a level 5 easily swallowable food and has high printing accuracy.In summary, flaxseed gum overcomes the contradictions between mechanical strength, textural tunability, and functional factor delivery efficiency in traditional protein gels through a triple mechanism of molecular-level structural adaptation, mesoscale phase behavior regulation, and macroscopic functional dynamic response, providing a reference for the development of gel foods for the elderly that combine swallowing safety and precise nutrition.

[0156] 3. Conclusion

[0157] This invention constructs a composite gel system of flaxseed gum and fish-derived myofibrillar protein through a multi-scale structural regulation strategy, providing theoretical and technical support for 3D printing technology and precise nutrient delivery of foods for elderly people with swallowing difficulties. At the molecular level, flaxseed gum induces secondary structure rearrangement of myofibrillar protein, reconstructing the hydrogen bond network of the gel. This reconstruction drives the secondary structure of myofibrillar protein from α-helices to β-sheets, reducing the hydrophobicity of the protein surface and effectively inhibiting the formation of coarse protein aggregates during heating. Furthermore, the network structure rearrangement optimizes the uniformity of oil droplet distribution in the gel system and significantly improves the encapsulation efficiency of lycopene through the synergistic effect of intermolecular polar groups. Macroscopic performance analysis shows that the chain entanglement and electrostatic repulsion effect of flaxseed gum endow the gel system with shear-thinning properties and thixotropic recovery, making it suitable for the dual requirements of high-precision extrusion and structural shape preservation in 3D printing processes. The LFG-3.5% gel system was classified as a level 5 easily swallowable food in IDDSI testing, and the printed product has a complete structure, allowing for customization of complex shapes according to individual needs. Simulated in vitro dynamic digestion experiments in the elderly showed that flaxseed gum effectively delayed the release of lycopene during gastric digestion, reducing its degradation risk in the acidic environment of the stomach. During intestinal digestion, the gel network swelled, promoting the release of lycopene and improving its bioavailability. The LFG-3.5% gel system exhibited the shortest gastric emptying time during in vitro dynamic gastric digestion, better matching the physiological characteristics of weakened gastric motility in the elderly and avoiding discomfort caused by prolonged gastric retention. This study innovatively integrated multi-scale structural analysis and dynamic digestion modeling techniques to elucidate the cascade mechanism of "intermolecular force rearrangement - network morphology evolution - digestive response correlation." This research not only provides insights for the rational design of swallowable 3D-printed foods for the elderly but also opens up a biomimetic-driven technological path for the development of functional foods based on physiological characteristics. In the future, digital modeling can be used to further optimize the structure-function adaptation framework, expanding its application potential in the field of multi-nutrient co-delivery.

[0158] Example 2

[0159] When the amount of gellan gum or gum arabic added 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 exhibit stratification during the heat induction process. Figure 9 and Figure 10 ).

[0160] A fish-derived protein gel system prepared using polysaccharides such as locust bean gum and guar gum (steps are the same as "1.3" in Example 1, except that locust bean gum or guar gum is used instead of flaxseed gum) exhibits poor compatibility with myofibrillar proteins. At high concentrations, phase separation occurs between the polysaccharides and the gel, preventing the formation of a homogeneous gel. At low concentrations (below 1 wt%), locust bean gum and guar gum can form a homogeneous gel with myofibrillar proteins. However, the locust bean gum-fish-derived protein gel and guar gum-fish-derived protein gel do not meet international dietary standards for dysphagia. As shown in the figure, in the spoon tilt test, the gel sample could not fall off smoothly even after tilting and gently shaking the spoon, leaving a significant amount of residue. This indicates that these two gels are highly viscous and easily adhere to the throat during swallowing, posing a risk of choking. Figure 11 ).

[0161] Lycopene encapsulation efficiency of different gels ( Figure 12 It can be found that when the polysaccharide addition is 0.75wt%, the lycopene encapsulation rate 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 preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a 3D-printed flaxseed gel fish-derived protein gel adapted to the swallowing and biomimetic digestive responses of the elderly, characterized in that, Includes the following steps: Fish-derived myofibrillar protein was prepared using oval pomfret as raw material. The fish-derived myofibrillar protein was then mixed evenly with a buffer solution to obtain a fish-derived myofibrillar protein solution. Lycopene and sunflower seed oil are mixed evenly to obtain a lycopene solution; the fish-derived myofibril protein solution and flaxseed gum are mixed evenly to obtain a flaxseed gum-fish-derived protein gel; the lycopene solution and the flaxseed gum-fish-derived protein gel are mixed evenly to obtain the 3D printed flaxseed gum-fish-derived protein gel. The concentration of lycopene in the lycopene solution is 1 mg / g; The final concentration of flaxseed gum in the 3D printed flaxseed gum fish protein gel is 3-4 wt%, the final concentration of lycopene solution is 10 wt%, and the final concentration of fish myofibril protein is 20 wt%.

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

3. The preparation method according to claim 1, characterized in that, The method for preparing the fish-derived myofibril protein includes the steps of successively crushing and centrifuging the flesh of oval pomfret.

4. The preparation method according to claim 3, characterized in that, The preparation method of the fish-derived myofibril protein specifically includes the following steps: The oval pomfret meat was crushed under ice bath conditions, then centrifuged three times in low phosphate buffer, and the resulting precipitate was centrifuged three times in high phosphate buffer. The resulting supernatant was stored in a refrigerator at 4°C for 2 hours, and then centrifuged again. The resulting supernatant was mixed with distilled water and precipitated, and then centrifuged twice more. The precipitate was collected to obtain the fish-derived myofibril protein.

5. The preparation method according to claim 4, characterized in that, The low-phosphate buffer solution comprises 0.005 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O, and 15.5 mmol / L Na2HPO4·12H2O; the high-phosphate buffer solution comprises 0.6 mol / L NaCl, 3.38 mmol / L NaH2PO4·2H2O, and 15.5 mmol / L Na2HPO4·12H2O.

6. A 3D-printed flaxseed gum fish protein gel obtained by the preparation method according to any one of claims 1-5.

7. The application of the 3D printed flaxseed gum fish protein gel according to claim 6 in the preparation of 3D printed food.

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