Inulin-induced porous structure improves rehydration performance of whole barley extruded noodles and preparation method thereof

Abstract

The application discloses a kind of inulin induced porous structure improvement rehydration performance whole green barley extruded noodles and preparation method thereof, belong to food preparation technical field. Including the following steps: inulin is dissolved in hot water, prepare inulin solution, green barley powder is mixed with the inulin solution and kneads, form uniform flocculate, the flocculate is sealed hydration, after hydration, the flocculate is extruded into shape by double screw extruder, obtain whole green barley extruded noodles;The temperature of the hot water is 40~50 ℃. Inulin adds prebiotic and nutrition fortification function to product as natural soluble dietary fiber. 6% inulin (degree of polymerization 15, molecular weight 2500‑3000Da) can promote the formation of more uniform and honeycomb porous structure in noodles, thereby improve water penetration and heat transfer efficiency, realize the best balance between "fast rehydration" and "quality maintenance".

Description

Technical Field

[0001] This invention relates to the field of food preparation technology, and in particular to an inulin-induced porous structure for improving rehydration properties of whole barley extruded noodles and its preparation method. Background Technology

[0002] Barley is an important grain crop unique to the Qinghai-Tibet Plateau. Its grains contain high levels of dietary fiber, β-glucan, protein, and various minerals and bioactive compounds, exhibiting significant nutritional advantages in blood sugar regulation, gut health promotion, and metabolic homeostasis. These characteristics have attracted increasing attention in the development of functional barley foods and healthy staple food products. However, developing barley into a staple food faces considerable challenges. Unlike the inherent viscoelastic gluten network structure of wheat, barley lacks this structural component, making it difficult to process into a staple food. Therefore, whole barley products (noodles, steamed buns, etc.) often exhibit poor processability, loose structure, coarse texture, and high cooking losses, which severely restricts their development.

[0003] Extrusion is a process that integrates feeding, compression, melting, and shaping, allowing for the direct production of noodle-shaped products under optimized conditions using molds. The resulting products typically exhibit enhanced chewiness and breakage resistance during cooking. This is primarily attributed to the gelation of starch during extrusion, where amylose and amylopectin interact to form a strong gel network, compensating for the lack of gluten. Studies have demonstrated the feasibility of extrusion technology for noodle production from crops such as buckwheat, quinoa, and rice. However, extruded noodles have a firm texture, limiting water penetration and prolonging cooking time. Generally, high-quality noodle products rehydrate within approximately 6 minutes. Despite the development of various extruded noodle products to date, most have failed to meet this rehydration benchmark. Therefore, the industrial application of whole barley extruded noodles (EWHBN) is limited not only by the lack of gluten-based structural support but also by its significantly impaired rehydration properties.

[0004] Several strategies have been explored to improve the rehydration efficiency of extruded noodle products, including creating porous structures, altering noodle network orientation, enhancing hydrophilicity, and manipulating starch gelatinization behavior. However, these methods face practical limitations: vacuum freeze-drying is too costly, while frying poses health risks. Similar principles are applied to extrusion processes, where rapid moisture evaporation near the die can create porous structures. However, achieving a uniform micropore distribution solely through parameter tuning remains challenging, limiting the industrial applicability of this approach. Fermentation is another option, generating pores through microbial metabolism and gas production, but it requires extended processing times, increasing production costs. While these methods offer improvements in replenishment, their effectiveness and scalability remain limited.

[0005] While existing technologies have attempted to improve rehydration efficiency through porous structures and altered network orientation, they have not effectively solved the rehydration performance problem of whole barley noodles, especially when combined with the effect of inulin.

[0006] Inulin is a naturally occurring soluble dietary fiber and prebiotic with excellent water retention and solubility, making it a valuable ingredient for optimizing the structure and fortifying the nutritional value of cereal products. Previous studies have shown that inulin enhances the texture properties of cereal foods by regulating system viscosity, redistributing moisture, and promoting pore formation. Furthermore, the addition of hydrophilic additives such as maltodextrin, sugar alcohols, and gelatin has been shown to create porous, loose structures in cooked noodles through dissolution or foaming mechanisms, leaving micropores. However, the use of inulin to construct EWHBNs to form porous structures and thus improve rehydration properties has not yet been reported. Existing technologies have reported the use of inulin in steamed buns and bread, but none have addressed the relationship between pore structure regulation and rehydration properties in barley noodles. Summary of the Invention

[0007] The purpose of this invention is to provide an inulin-induced porous structure for improving the rehydration performance of whole barley extruded noodles and its preparation method, thereby addressing the problems existing in the prior art. This invention aims to evaluate the effect of different inulin concentrations on the rehydration quality of EWHBN, focusing on the quality characteristics of barley flour, starch structure transformation, noodle microstructure, and rehydration behavior. The main objective of this invention is to elucidate the mechanism by which inulin enhances the rehydration performance of EWHBN.

[0008] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing whole barley extruded noodles with inulin-induced porous structure to improve rehydration performance, comprising the following steps: Inulin is dissolved in hot water to prepare an inulin solution. Barley flour is mixed with the inulin solution and kneaded to form a uniform flocculent. The flocculent is sealed and hydrated. The hydrated flocculent is then extruded through a twin-screw extruder to obtain whole barley extruded noodles. The temperature of the hot water is 40~50℃.

[0009] The second technical solution of the present invention is a whole barley extruded noodle with inulin-induced porous structure to improve rehydration performance, which is prepared by the aforementioned preparation method.

[0010] Based on the above technical solution, the present invention has the following technical effects: This invention successfully produced whole-barley extruded noodles with significantly improved rehydration performance by introducing a specific proportion of inulin (especially 6%) into barley flour and employing a twin-screw extrusion process. Inulin, with its strong hydrophilicity and molecular entanglement, induces the formation of a uniform, honeycomb-like porous microstructure within the noodles, providing rapid channels for water penetration and enhancing the fluidity of weakly bound water. This significantly reduces the rehydration time from 10.74 minutes to 7.35 minutes (a reduction of 31.6%) and improves thermal conductivity. An appropriate amount of inulin (≤6%) also maintains low cooking loss (<8%) and breakage rate (approximately 11.7%), preventing noodle structural collapse and maintaining acceptable noodle firmness, elasticity, and chewiness while significantly improving rehydration behavior. Furthermore, as a natural soluble dietary fiber, inulin adds prebiotic and nutritional fortification functions to the product. In summary, this invention achieves a good balance between rapid rehydration, reduced cooking energy consumption, preservation of edible quality, and enhanced nutritional value, providing an efficient and feasible technical solution for the industrial production of high-fiber whole-grain staple foods. Attached Figure Description

[0011] Figure 1 Water absorption index (A), water solubility (B), gelatinization curve (C), viscosity, and gelatinization temperature (D) of barley flour with different inulin concentrations are shown. Different lowercase letters for the same parameter indicate significant differences (P<0.05). Percentage values ​​represent the inulin content (w / w%) added to the barley flour formulation.

[0012] Figure 2 Rheological properties and gel strength of gelatinized highland barley flour with different inulin concentrations. Storage modulus G' (solid symbol) and loss modulus G'' (hollow symbol) at frequency scans (A), and loss tangent tanδ (B). Force-time curves of the mixed gel (C) and puncture force (D).

[0013] Figure 3 LF-NMR spectra of whole barley extruded noodles (EWHBN) with different inulin concentrations. LF-NMR curves (A), relaxation time (T2) (B), and water ratios at different states (C).

[0014] Figure 4 FITR and X-ray diffraction patterns of EWHBN with different inulin concentrations. FITR spectrum (A), deconvolutioned FTIR spectrum (B), FTIR spectra at 1047 and 1022 cm⁻¹. -1 The ratio (C) and XRD curve (D) at the point.

[0015] Figure 5 SEM images of EWHBN with different inulin concentrations.

[0016] Figure 6Pore ​​distribution diagram of EWHBN at different inulin concentrations.

[0017] Figure 7 The rehydration behavior and cooking quality of EWHBN under different inulin concentrations. Rehydration time (A), rehydration rate (B), breakage rate (C), cooking loss (D).

[0018] Figure 8 Thermal conductivity and tensile properties of EWHBN at different inulin concentrations. Thermal conductivity (A), tensile properties (B), tensile length (C), and tensile strength (D).

[0019] Figure 9 Texture properties of EWHBN at different inulin concentrations: hardness (A), viscosity (B), elasticity (C), and chewiness (D).

[0020] Figure 10 A diagram illustrating the mechanism by which inulin regulates the rehydration behavior of EWHBN.

[0021] Figure 11 This diagram illustrates the mechanism by which inulin induces the formation of porous structures in EWHBN and improves its rehydration performance. Detailed Implementation

[0022] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0023] This invention provides a method for preparing whole barley extruded noodles with improved rehydration properties due to inulin-induced porous structure, comprising the following steps: Inulin is dissolved in hot water to prepare an inulin solution. Barley flour is mixed with the inulin solution and kneaded to form a uniform flocculent. The flocculent is sealed and hydrated. The hydrated flocculent is then extruded through a twin-screw extruder to obtain whole barley extruded noodles. The temperature of the hot water is 40~50℃.

[0024] In some specific implementations, the mass ratio of inulin, water, and highland barley flour is 6:40:100.

[0025] In some specific implementations, the hydration is specifically described as hydration by standing at room temperature for 8 to 12 hours.

[0026] In some specific implementations, the process parameters of the twin-screw extruder are as follows: screw diameter 20 mm, length-to-diameter ratio 40:1, die diameter 1 mm, screw speed 120±5 rpm, feed rate 25±5 g / min, and extrusion temperature zones of 40±5 ℃, 6±5 ℃, 100±5 ℃, 100±5 ℃, 80±5 ℃, and 80±5 ℃.

[0027] This invention also provides an example of whole barley extruded noodles with inulin-induced porous structure to improve rehydration performance, prepared by the aforementioned method.

[0028] In some specific embodiments, the noodles have a porous structure with a cross-sectional pore size distribution of 0~30 μm and a porosity of 9%~13%.

[0029] In some specific implementations, the rehydration time for the noodles is 7.35 minutes.

[0030] Example 1 1. Materials Barley flour (Kunlun 15, moisture content 7.70%, ash content 1.61%, total starch 68.70%, crude protein 9.83%, crude fat 1.82%, crude fiber 1.39%). Inulin (degree of polymerization 15, molecular weight 2500–3000 Da). All other chemicals used in this study were of analytical grade.

[0031] 1.1 Measurement of hydration characteristics The hydration properties of the samples were determined according to the method of Li et al. (2026), with slight modifications. Specifically, inulin was dissolved in warm water at concentrations of 0%, 3%, 6%, 9%, 12%, and 15% (w / w, based on flour). Subsequently, 3 g of wheat flour was mixed with 30 mL of each inulin solution and stirred and dispersed for 30 min at two different temperatures: 25 °C and 100 °C. The dispersions were then cooled at 4 °C for 3 min. After centrifugation at 15000 g for 30 min, the supernatant was transferred to an aluminum pan and dried at 105 °C until constant weight was achieved. The weights of the wet precipitate and the dried supernatant were measured to calculate the water absorption index and water solubility.

[0032] 1.2 Gelatinization Characteristics Determination Following the method described by Kuang et al. (2021), the viscosity characteristics of the samples were determined using a rapid viscosity analyzer. Briefly, 28 g suspensions were prepared by mixing barley flour (2.4 g dry basis) with inulin solutions of varying concentrations. After homogenization, the mixture was subjected to programmed heating and cooling cycles. The gelatinization temperature, peak viscosity, and decomposition viscosity were recorded after testing.

[0033] 1.3 Rheological property determination Rheological measurements were performed according to the method proposed by Zhong et al. (2025), with some modifications. Specifically, the prepared cooled gel samples were placed on a DHR-3 rheometer equipped with a 40 mm parallel plate geometry. Before measurement, the samples were equilibrated at 25 °C and heated at 25 °C for about 1 minute to ensure thermal stability. Dynamic frequency scanning was performed in the frequency range of 0.1–10 Hz at 1% linear viscoelastic strain.

[0034] 1.4 Gel strength determination Gel samples were placed in a cylindrical mold for texture characterization. Texture profiles were assessed using a food texture analyzer equipped with a cylindrical TA / 0.5 probe under controlled parameters: 0.5 N trigger force, 5 mm / s approach velocity, 1 mm / s compression rate, 5 mm / s retraction velocity, and 10 mm deformation depth. The structural strength of the gel was quantitatively assessed by measuring the maximum normal force applied during the initial penetration of the gel network; this normal force represents the gel strength.

[0035] 1.5 Preparation of whole barley extruded noodles (EWHBN) Weigh out the raw materials: barley flour, water, and inulin in a weight ratio of 100:40:(0-15).

[0036] Inulin solutions (0%, 3%, 6%, 9%, 12%, 15%, w / w) were prepared in water. Barley flour was then mixed with the inulin solutions (based on the weight of the barley flour) and kneaded until a homogeneous flocculent was formed. The mixture was sealed under a plastic film and hydrated overnight. EWHBN samples were processed using a twin-screw extruder with the following parameters: screw diameter 20 mm, L / D ratio 40:1, die 1 mm, screw speed 120 ± 5 rpm, feed rate 25 ± 5 g / min, and extrusion temperatures of 40 ± 5 ℃, 6 ± 5 ℃, 100 ± 5 ℃, 100 ± 5 ℃, 80 ± 5 ℃, and 80 ± 5 ℃. EWHBN samples with different inulin levels were designated as 0%, 3%, 6%, 9%, 12%, and 15%. For analysis, samples were freeze-dried, ground, and sieved through an 80-mesh sieve before storage.

[0037] 1.6 Moisture Distribution Analysis Based on the method established by X. Xu et al. (2022), the transverse relaxation time (T2) of samples was analyzed using an LF-NMR system. Briefly, equal-mass EWHBN samples with different inulin levels were packed into 25 mm inner diameter NMR tubes and sealed. Measurements were performed using a multi-echo Q-CPMG pulse sequence with the following instrument settings: 20 kHz scan frequency, 0.3 ms echo time, 7000 echoes, and 4 scans. Data were processed and inverted using the instrument's built-in software.

[0038] 1.7 Fourier Transform Infrared Spectroscopy Analysis The infrared absorption spectra of the samples were collected using an FTIR spectrometer. Specifically, the dried samples were ground and mixed with KBr at a ratio of 1:60, then compressed into particles. The Fourier transform infrared spectra were obtained in the range of 400–4000 cm⁻¹. -1 Collection within range -1 Resolution 4cm -1Each spectrum was scanned 32 times. Baseline correction and deconvolution were performed on the acquired spectra using OPUS 7.2 software.

[0039] 1.8 X-ray diffraction (XRD) determination The crystal structure of starch was investigated using X-ray diffraction (XRD) under Cu Kα radiation at 20 kV and 10 mA. Diffraction patterns were collected in the 2θ range of 5°–40° at a scan rate of 6° / min and a step size of 0.02°. The obtained XRD patterns were analyzed using Jade 5.0 software, and the relative crystallinity was calculated to assess the changes in long-range ordered structure.

[0040] 1.9 Scanning Electron Microscopy (SEM) Observation After freeze-drying, the EWHBN sample was cut into small segments, mounted on a sample stage, and sputter-plated with gold. The cross-section, surface, and internal structure were observed using SEM at 15 kV. ImageJ software was used to analyze the micrographs and determine the pore size distribution and porosity.

[0041] 1.10 Determination of the rehydration performance of EWHBN The rehydration time and ratio were slightly modified from the method of Zhang et al. (2022). Noodles of uniform length were selected and cooked in boiling water until the white core of the noodles completely disappeared; the time elapsed was recorded as the rehydration time. After the cooking solution was dried to constant weight, the initial dry mass of the noodles (m0), the initial number of noodles (n0), the mass of the rehydrated noodles (m1), the number of rehydrated noodles (n1), and the mass of the dried residue of the noodle soup were measured.

[0042] 1.11 Thermal conductivity analysis Following the method proposed by Jang et al. (2016), thermal conductivity was measured using a C-Therm TCi analyzer with minor modifications. Cooked noodles were cooled and placed on the thermal sensor, with a fixed weight applied to ensure firm contact. The thermal conductivity value was determined based on the slope of the sensor response curve using a modified transient planar source method.

[0043] 1.12 Tensile strain and texture property analysis The tensile and textural properties of the samples were measured using a TA-XT Plus texture analyzer. Specifically, force-time curves were recorded using the equipped A / SPR probe under the following conditions: a test speed of 90 mm / min, an initial distance of 30 mm, and a trigger force of 0.4 N. The tensile length and tensile strength were then calculated. Furthermore, the texture properties of the noodles were evaluated using a P36 / R probe at a test speed of 90 mm / s, a trigger force of 0.5 N, and 75% deformation in two cyclic compression tests. After testing, parameters such as hardness, adhesion, elasticity, and chewiness were recorded.

[0044] 2. Experimental Results 2.1 Quality Characteristics of Highland Barley Flour 2.1.1 Hydration characteristics like Figure 1 As shown in Figure A, the effect of inulin addition level on the water absorption index of barley flour was evaluated at two different temperatures (25℃ and 100℃). Notably, the water absorption index gradually decreased with increasing inulin content, and a significant temperature-dependent enhancement was observed in all samples. This phenomenon can be attributed to the gelatinization process, where starch granules undergo structural expansion and degradation, thereby enhancing their physicochemical interactions with water / inulin molecules and improving their water-binding capacity.

[0045] Compared to the water absorption index, the water solubility of barley flour exhibited the opposite trend. Water solubility increased in a dose-dependent manner with increasing inulin content, a trend exacerbated under thermal conditions. The observed increased solubility primarily stemmed from the inherently high solubility of inulin in aqueous environments, where it acted as a solubilizer during heat treatment. Specifically, thermally induced structural reorganization of inulin molecules may have generated a more hydrophilic matrix, promoting the leaching of water-soluble components from barley flour.

[0046] 2.1.2 Gelatinization performance With the increase of inulin addition, the gelatinization temperature gradually increases. Figure 1 (C and D in the original text). This phenomenon is generally attributed to the competitive water-binding capacity of the highly hydrophilic component, which reduces the available water for starch gelatinization and requires higher temperatures to initiate the process. Meanwhile, as the inulin content increased from 0% to 15%, the peak viscosity of the sample decreased from 4518 cP to 2787 cP, indicating that inulin inhibited starch gelatinization behavior. Starch gelatinization involves the breaking of hydrogen bonds in amylose and amylopectin, followed by the dissolution and entanglement of starch chains in water, thus increasing viscosity. The high solubility of inulin may promote stronger interactions with amylose, reducing direct contact between amylose and water molecules, thereby lowering gelatinized viscosity. Furthermore, the competitive water absorption between inulin and starch also reduces the effective water content in the system, potentially limiting the expansion of starch granules and leading to the observed decrease in peak viscosity.

[0047] Simultaneously, the decomposition viscosity significantly decreased from 4868 cP to 3469 cP. Decomposition viscosity, defined as the difference between the peak and minimum viscosity, reflects the thermal stability of the gelation system. The lower decomposition value indicates reduced starch granule destruction and inhibited gelation. These results suggest that inulin, due to its abundant hydrophilic groups, adsorbs water molecules onto the surface of starch granules, forming a protective coating that hinders gelation. Generally, the hydrophilic interaction between inulin and water outweighs the hydrogen bonds within the starch granules. Therefore, during mixing and heating, the rigidity / stability or anti-swelling property of the starch granules is enhanced, leading to a decrease in decomposition viscosity during gelation. In summary, the inhibitory effect of inulin on starch gelatinization is a result of the combined effects of inulin-amylose molecular interactions and inulin-mediated regulation of water utilization.

[0048] 2.1.3 Rheological properties Dynamic rheological measurements are crucial for evaluating the mechanical properties and viscoelastic behavior of gel networks in food systems. For example... Figure 2 As shown in Figure A, the storage modulus (G') and loss modulus (G'') of all samples increase frequency-dependently with increasing angular frequency. Notably, within the tested frequency range (0.1-10 Hz), G' consistently exceeds G'', indicating that elastic behavior dominates the system, a typical characteristic of traditional gel networks. With increasing inulin content, the viscoelastic curves all show a downward shift. The decrease in modulus indicates that inulin incorporation weakens the barley flour gel network, leading to reduced mechanical strength.

[0049] like Figure 2 As shown in Figure B, the tanδ values ​​of all samples were below 1 across the entire frequency range, further confirming the elastic advantage of the barley flour gel system. However, the tanδ value increased significantly with increasing inulin content, indicating a shift from rigid gel to more fluid-like behavior. This phenomenon can be attributed to the encapsulation of starch granules by inulin molecules and the strong interaction between inulin and amylose. These effects inhibit the formation of a three-dimensional network during the cooling process of amylose gelation, ultimately leading to more fluid-like rheological behavior.

[0050] 2.1.4 Gel strength To further investigate the effect of inulin on the gel network structure of highland barley flour, the gel strength of different samples was characterized. All samples exhibited similar force-time curves, characterized by a rapid increase in force during the initial 0-10 s phase, followed by a gradual decrease during the retraction phase, eventually reaching equilibrium. Figure 2 (C). The gel's resistance to deformation was quantitatively assessed using permeability as a metric. Figure 2(D). The results showed that inulin significantly reduced the gel strength of barley flour gel in a concentration-dependent manner. Specifically, as the inulin content increased from 0% to 15%, the puncture force decreased from 0.61 N to 0.35 N, a reduction of 42.6%. This indicates that the addition of inulin reduces the cross-linking density between starch molecules, weakening the gel network formed during cooling, further supporting the rheological finding that inulin inhibits starch cross-linking. This effect ultimately inhibits the formation of a three-dimensional gel network after gelation, leading to a decrease in gel strength.

[0051] 2.2 Structural transformation of EWHBN 2.2.1 Moisture Distribution The migration rate and distribution of water molecules in whole barley extruded noodles (EWHBN) were studied using low-field nuclear magnetic resonance (LF-NMR). Figure 3 As shown in Figure A, the moisture distribution curves of EWHBN with different inulin concentrations show two distinct transverse relaxation time components: T 21 (0.1-10 ms) corresponds to the tightly bound water in the retrograde starch crystallization region, T 22 (10-300 ms) represents weakly bound water in amorphous and semi-crystalline domains. Notably, the presence of inulin significantly reduced T compared to the control sample without inulin. 21 and T 22 relaxation time ( Figure 3 (B) At the same time, T was observed. 22 The T² relaxation distribution exhibits an inverse concentration-dependent relationship, gradually decreasing with increasing inulin content. This phenomenon is consistent with previous findings that a narrower T² relaxation distribution typically indicates a faster molecular exchange rate and a more uniform proton mobility. 22 The reduction in relaxation time indicates that the water-inulin interaction is enhanced through a more stable hydrogen bond network.

[0052] The total integral area (A2) of the peaks in EWHBN reflects the relative water content ( Figure 3 (C). It has been proven that after adding inulin, A 21 (corresponding to T) 21 A significantly decreased 22 (corresponding to T) 22The concentration-dependent trend further emphasizes the reorganization of water distribution induced by inulin incorporation. The observed increase in weakly bound water content can be attributed to the hydrophilicity of inulin, characterized by numerous hydroxyl groups acting as hydrogen bond acceptors. These polar groups form directional hydrogen bonds with water molecules (hydrogen bond donors), thereby fixing water within the gel network and reducing the proportion of water bound to the starch and protein matrix. Recent studies on dried rice flour have shown that treatment with 1,4-α-glucan branching enzymes promotes water molecule distribution within the gel network, facilitates water migration and penetration during heat treatment, and accelerates the recovery of noodle elasticity. Based on these findings, it is reasonable to hypothesize that the increased mobile water content in EWHBN with added inulin may be a key factor in shortening noodle rehydration time.

[0053] 2.2.2 Fourier Transform Infrared Spectroscopy like Figure 4 As shown in Figure A, the FTIR spectra of the samples with and without inulin are essentially the same, and no new absorption peaks were observed, indicating that the presence of inulin did not alter the starch molecules or generate new chemical bonds or functional groups. Therefore, no covalent interaction was formed between inulin and starch. (3000-3600 cm⁻¹) -1 The band corresponds to the OH stretching vibration region and is related to the strength of hydrogen bonds between starch molecules. Notably, as the inulin concentration increases from 0% to 15%, the characteristic absorption peak shifts to lower wavenumbers (from 3430 cm⁻¹). -1 up to 3420 cm -1 The redshift and broad spectral bands indicate a significant weakening of hydrogen bond strength in the system, likely a result of competitive hydrogen bonding between inulin hydroxyl groups and starch molecules. This finding is consistent with the hypothesis of reduced viscoelasticity inferred from rheological properties.

[0054] To further explore the effect of inulin on short-range ordered starch formation, the study focused on the 970-1060 cm⁻¹ region. -1 Unconvolution of the original spectrum within the range ( Figure 4 (Middle B). 1047 cm -1 and 1022 cm -1 The characteristic peaks at these locations correspond to the crystalline and amorphous regions of starch, respectively. The peak area ratio (R0) is... 1047 / 1022 Used to reflect the short-range order of starch molecules ( Figure 4 C). When the inulin content exceeds 3%, observe R. 1047 / 1022The ratio decreased by 33.3% from 0.51 in the control group to 0.34 in the sample containing 15% inulin. These results indicate that inulin disrupts the short-range ordered structure of starch in EWHBN, altering the conformation of starch molecules. This change in the short-range ordered structure of starch molecules is primarily attributed to the potential formation of a network between longer, highly branched inulin molecules and shorter amylopectin fragments. Through physical entanglement and competitive hydrogen bonding, this network enhances the interaction between inulin and starch chains, thereby inhibiting the ordered assembly of the starch double helix and the formation of crystalline regions.

[0055] 2.2.3 X-ray diffraction The crystallinity of starch in EWHBN was determined by XRD to assess its long-range ordered structure. Figure 4 As shown in Figure D, all samples exhibited distinct diffraction peaks at approximately 20°, characteristic of the typical V-shaped crystal structure formed by the complexation of amylose and lipids. This result indicates that the addition of inulin does not alter the crystallinity of starch. Clearly, the peak intensity gradually decreased with increasing inulin content, suggesting a gradual shift towards an amorphous state in the starch structure. For example, when the inulin content increased from 0% to 15%, the relative crystallinity decreased from 10.87% to 6.84%. This phenomenon may be attributed to the entanglement of inulin chains with amylopectin and / or amylose, which effectively weakens the intermolecular interactions between amylose and amylopectin, thereby inhibiting the recrystallization process. The decrease in the crystalline region corresponds to the increase in the amorphous region, which promotes water molecule penetration and accelerates the rehydration process. This observation is consistent with previous conjectures regarding the distribution of water molecules.

[0056] 2.2.4 Microscopic morphology Figure 5 The cross-sectional, surface, and internal microstructures of EWHBN containing different levels of inulin are shown. Clearly, the cross-sectional structure of inulin-free EWHBN is compact; the noodle surface is smoother with almost no observable pores, and the noodle interior appears denser, explaining the prolonged rehydration time. In contrast, the addition of inulin results in a porous and honeycomb-like structural feature on both the surface and interior of the EWHBN. With increasing inulin content, the pore size gradually increases, and the internal gel network structure gradually loosens. The porous structure of the noodles provides channels for water to penetrate the interior; larger or more numerous pores make it easier for water to enter the noodle core, thereby increasing water absorption, promoting efficient heat / mass transfer during cooking, and ultimately shortening cooking time.

[0057] However, when the inulin content exceeded 6%, the dense micropores on the surface gradually transformed into loose macropores that interconnected, reducing the uniformity and continuity of the internal gel structure. This indicates that excessive inulin leads to the collapse of the noodle's pore structure, the rupture of the dense gel network, and may result in discontinuous pore walls, reduced mechanical strength, and increased cooking losses, consistent with previous reports. Therefore, it can be inferred that an appropriate level of inulin inducing a uniform porous structure and continuous gel network in noodles may be key to improving the rehydration quality of EWHBN.

[0058] 2.2.5 Pore size distribution To further elucidate the effect of inulin on the pore size and porosity of EWHBN, quantitative analysis was performed on surface micrographs. Figure 6 The white areas in the diagram represent the pore distribution on the EWHBN surface. Clearly, inulin-free EWHBN exhibits the smallest visible pores on its surface, evidenced by its low porosity of 1.34%. In contrast, inulin incorporation gradually increases the number of pores and results in a more uniform distribution, particularly evident in EWHBN with 6% inulin. The cross-sectional pore size of inulin-free EWHBN is 5.74 μm, while the pore size increases to 11.15 μm with inulin addition, and the porosity increases to 13.02%. Notably, the cross-sectional pore size distribution of EWHBN containing 6% inulin is primarily between 0-30 μm, achieving a more uniform structure with a porosity of 9.64%. However, with further increases in inulin content, the pore size distribution widens, with some pores exceeding 60 μm. This indicates that further increases in inulin content excessively increase porosity, leading to the formation of discontinuous and uneven pores, potentially resulting in network structure damage and reduced structural support. Therefore, an appropriate inulin content significantly increased the number and size of pores on and inside the EWHBN surface, with pore diameters reaching tens of micrometers. The resulting network structure remained relatively uniform and less open, which constitutes a fundamental characteristic of high-quality products. These findings further confirm the observations from the microstructure analysis.

[0059] 2.3 Rehydration performance of EWHBN 2.3.1 Rehydration Behavior Rehydration time is a key quality parameter for extruded noodles, playing a decisive role in consumer acceptance. The rehydration time and rehydration rate of EWHBN with different inulin contents are as follows: Figure 7As shown in Figures A and B, the rehydration time and rehydration rate of EWHBN significantly decreased with increasing inulin content. Specifically, as the inulin content increased from 0% to 15%, the rehydration time decreased from 10.74 minutes to 4.46 minutes (a reduction of 58.5%), while the rehydration rate decreased from 282.94% to 159.98% (a reduction of 43.5%). Notably, compared to the control group, the sample containing 6% inulin showed a significant reduction in both rehydration time (7.35 minutes, a reduction of 31.6% compared to the control group) and rehydration rate (229.19%, a reduction of 19.0% compared to the control group). This result is likely primarily attributed to the strong hydrophilicity of inulin, which promotes rapid absorption and penetration of water into the noodle matrix, thereby accelerating hydration and shortening cooking time. Furthermore, the shortened rehydration time of EWHBN may be closely related to its pore structure characteristics. As shown in the SEM observations above, the incorporation of inulin induces the formation of a more extensive porous microstructure within the noodle matrix. These microscale pores increase the specific surface area available for water contact, facilitate water diffusion, and enhance the mass transfer rate during rehydration.

[0060] 2.3.2 Cooking characteristics To further evaluate the structural integrity of EWHBN after rehydration, its cooking performance was assessed. For example... Figure 7 As shown in Figure C, appropriate levels (≤6%) of inulin incorporation have little effect on the breakage rate of rehydrated EWHBN, which remains relatively stable at around 11.7%, consistent with the findings of Gao et al. (2023) on rice noodles. However, when the inulin content exceeds 6%, the breakage rate increases significantly. This behavior is mainly attributed to the interaction between the polar functional groups of inulin and the hydroxyl groups of starch molecules, which partially replaces the intermolecular hydrogen bonds between starch chains. This interaction weakens molecular association in the starch matrix, thereby reducing the tensile strength of the noodles. Consistent with microstructure observations, excessive inulin incorporation reduces the uniformity and continuity of the internal gel network, decreases mechanical stability, and ultimately leads to a higher breakage rate.

[0061] The trend of cooking loss was similar to that of breakage rate. Specifically, the cooking loss of EWHBN samples containing less than 6% inulin was approximately 7.2% ( Figure 7According to Bharath and Prabhasankar (2015), cooking loss of less than 8% is generally considered a hallmark of high-quality noodles, indicating that appropriate inulin addition (≤6%) can maintain ideal cooking properties. In contrast, when the inulin content reached 15%, cooking loss increased significantly to 12.3%, a 70.8% increase relative to the control group, indicating a significant deterioration in noodle quality. The increased cooking loss in EWHBN is likely due to two main factors: first, inulin dissolves in boiling water, preventing it from effectively participating in network formation; second, the network opening effect caused by excessive inulin incorporation weakens the internal structural integrity during cooking. Therefore, the water-holding capacity of the noodles decreases, and more soluble components leach out, leading to increased cooking loss. These findings are consistent with the observed changes in breakage rate, further confirming that excessive inulin addition has an adverse effect on the structural stability of EWHBN during cooking.

[0062] 2.3.3 Thermal conductivity The effect of inulin incorporation on the thermal conductivity of cooked EWHBN is as follows: Figure 8 As shown in Figure A, the results indicate that the thermal conductivity of the cooked noodles ranges from 0.393 to 0.462 W / m·K. Notably, the EWHBN with added inulin exhibits significantly higher thermal conductivity than the control group without inulin, and this parameter gradually increases with increasing inulin content. These findings suggest that the incorporation of inulin has a positive effect on improving the thermal conductivity of EWHBN.

[0063] Generally, the thermal conductivity of a material is closely related to its structural properties, with porous and water-absorbing structures being more conducive to heat transfer. The addition of inulin promotes the formation of a more uniform porous structure in EWHBN, which may help to absorb water quickly during cooking, thereby improving thermal conductivity, indicating a positive correlation between thermal conductivity and cooking time.

[0064] 2.4 Edible quality of EWHBN 2.4.1 Tensile properties The tensile properties of rehydrated EWHBN are as follows Figure 8 As shown in Figure B, this is an important indicator for evaluating the quality of rehydrated noodles, closely related to sensory properties, especially texture. All samples exhibited similar tensile behavior: tensile force gradually increased with stretching until reaching maximum elongation, then dropped sharply once the breaking point was exceeded. This behavior indicates that the gel-like network was reconstructed during cooking. With the absorption of water, the fluidity and flexibility of the starch molecular chains increased, thereby improving the tensile strength of the noodle matrix. However, once the critical tensile threshold was exceeded, the gel network could not withstand the applied stress, leading to structural breakage and a significant loss of tensile strength.

[0065] Figure 8Tables C and D further illustrate the tensile length and strength of rehydrated EWHBN at the optimal rehydration time. A significant negative correlation exists between inulin content and tensile length and strength. Specifically, as the inulin content increases from 0% to 15%, the maximum tensile length decreases from 29.8 mm to 4.9 mm (a reduction of 83.6%), while the tensile strength decreases from 1.13 N to 0.51 N (a reduction of 54.9%). These findings suggest that the addition of inulin weakens the texture and strength of the noodles. This effect is closely related to the development of the porous microstructure.

[0066] Notably, the maximum elongation decreased sharply when the inulin content exceeded 6%. This result indicates that while higher levels of inulin may accelerate rehydration, they can also impair the structural integrity and cooking performance of noodles. Therefore, an appropriate level of inulin is needed to achieve a balance between ideal texture and rehydration performance in EWHBN. Previous studies have also noted a similar phenomenon, where the addition of appropriate plasticizers can enhance the texture of rice noodles. This conclusion is consistent with the rehydration quality results and further supports the finding that inulin-induced structural changes directly affect the cooking properties of noodles.

[0067] 2.4.2 Texture characteristics Texture characteristics are one of the most important indicators of the core quality of noodle products. TPA was used to evaluate the texture properties of EWHBN. Typically, stiffness is defined as the maximum force required to achieve a specific deformation of the noodle matrix, thus reflecting its resistance to external mechanical stress. Adhesion represents the energy required to separate the probe from the noodle surface after contact, while elasticity represents the sample's ability to recover its original shape after the applied force is removed. Chewability was calculated as a composite parameter representing the energy required to chew the noodles to a swallowable state. Figure 9 As shown in the AD diagram, besides the increasing adhesiveness, the increase in inulin content led to a gradual decrease in the hardness, elasticity, and chewiness of EWHBN. For example, as the inulin content increased from 0% to 15%, the hardness decreased from 76.72 g to 26.56 g, a decrease of 65.4%. This trend is consistent with the tensile test results, indicating that the addition of inulin weakens the texture integrity of rehydrated noodles. As a water-soluble dietary fiber, inulin is composed of linear polysaccharide chains and may compete with starch molecules for interaction sites in the gel network. During rehydration, inulin can interact with starch chains through non-covalent hydrogen bonds, thereby disrupting the continuity and strength of the starch-based gel matrix. Therefore, the noodles form a looser three-dimensional network structure, which directly leads to the deterioration of texture, especially the reduction in hardness and elasticity.

[0068] 2.5 Regulation Mechanism Based on the above findings, a simplified mechanistic model is proposed to explain the role of inulin in regulating EWHBN quality. Figure 10Inulin primarily functions through its high hydrophilicity, molecular entanglement, and competitive hydrogen bonding capabilities, thereby modulating water distribution, starch structure evolution, and noodle network structure. During flour hydration and extrusion, inulin competes with starch for water molecules, reducing starch swelling and weakening gelatinization. Simultaneously, inulin interacts with starch chains through non-covalent hydrogen bonds and physical entanglement, disrupting the recombination of amylose and limiting the formation of a dense gel network. Furthermore, inulin promotes the development of the porous structure of EWHBN. An appropriate inulin addition (6%) helps form uniformly distributed pores, enhancing the fluidity of weakly bound water, thus improving water permeability and heat transfer during rehydration. These structural changes contribute to shorter rehydration time and improved cooking efficiency. However, excessive inulin disrupts network continuity, excessively enlarges pore size, and weakens structural integrity, thereby increasing cooking loss and breakage rates. Overall, a 6% inulin content achieves an optimal balance between rapid rehydration and acceptable dietary quality.

[0069] In summary, the addition of inulin, especially at appropriate concentrations, can effectively improve the rehydration quality of EWHBN. Adding an appropriate amount of inulin (6%) promotes the formation of a more uniform and honeycomb-like porous structure in the noodles, thereby improving water penetration and heat transfer efficiency. Compared to the control group, this structural optimization significantly shortened the rehydration time by 31.6% (7.35 minutes). Notably, breakage and cooking loss remained within acceptable ranges, with the lowest breakage rate (11.7%) and cooking loss (7.6%), indicating that inulin can effectively improve rehydration efficiency without affecting product edibility. However, excessively high inulin content (>6%) disrupts the continuity of the internal gel network, weakens the intermolecular interactions between starch molecules, thereby reducing structural stability, leading to a significant increase in cooking loss, and adversely affecting overall product quality. Overall, a 6% inulin addition level (degree of polymerization 15, molecular weight 2500-3000 Da) represents the optimal balance between "rapid rehydration" and "quality retention." As a natural, water-soluble dietary fiber, inulin shows great industrial potential in the production of high-quality extruded noodles. Future research should integrate consumer sensory evaluations, storage stability assessments, and nutrient digestibility analyses to validate its application value in whole wheat noodle systems.

[0070] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing whole barley extruded noodles with inulin-induced porous structure to improve rehydration performance, characterized in that, Includes the following steps: Inulin is dissolved in hot water to prepare an inulin solution. Barley flour is mixed with the inulin solution and kneaded to form a uniform flocculent. The flocculent is sealed and hydrated. The hydrated flocculent is then extruded through a twin-screw extruder to obtain whole barley extruded noodles. The temperature of the hot water is 40~50℃.

2. The preparation method according to claim 1, characterized in that, The mass ratio of inulin, water, and highland barley flour is 6:40:

100.

3. The preparation method according to claim 1, characterized in that, The hydration process specifically involves allowing the water to stand at room temperature for 8-12 hours.

4. The preparation method according to claim 1, characterized in that, The process parameters of the twin-screw extruder are as follows: screw diameter 20 mm, length-to-diameter ratio 40:1, die diameter 1 mm, screw speed 120±5 rpm, feed rate 25±5 g / min, and extrusion temperature zones of 40±5 ℃, 6±5 ℃, 100±5 ℃, 100±5 ℃, 80±5 ℃, and 80±5 ℃.

5. A whole barley extruded noodle with inulin-induced porous structure to improve rehydration performance, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. The whole barley extruded noodles according to claim 5, characterized in that, The noodles have a porous structure with a cross-sectional pore size distribution of 0~30 μm and a porosity of 9%~13%.

7. The whole barley extruded noodles according to claim 5, characterized in that, The rehydration time for the noodles is 7.35 minutes.

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