Digestibility Of Wheat Starch Research Articles

Effect of Ethanol Extract of Tea on the Physicochemical, Retrogradation Characteristics, and Digestion Properties of Wheat Starch

AbstractThe effects of ethanol extract of tea (EET) on the physicochemical properties, microstructure, and digestibility of wheat starch (WS) are investigated. Aging degree, solubility, swelling degree, Springness of gel, thermodynamic properties, X‐ray diffraction, infrared spectroscopy, Scanning electron microscopy (SEM), and digestibility of WS by adding different ratios of EET are analyzed. The changes of EET on WS‐related properties are evaluated comprehensively. The results show that the addition of EET reduces the enthalpy of recovery and inhibits the recovery of WS. At the same time, XRD diffraction shows that the addition of EET reduces the crystallinity of WS. At the same time, the addition of EET also decreases the content of rapidly digestible starch (RDS) in WS and increases the content of slowly digestible starch (SDS) and resistant starch (RS). In conclusion, EET can inhibit the retrogression of WS and can also be used as a potential source of RS additives.

Effects of galactomannans of varied structural features on the functional characteristics and in vitro digestibility of wheat starch

This study explores the effects of four natural galactomannans (GMs) with varying degrees of branching (fenugreek gum, guar gum, tara gum and locust bean gum) on the functional properties and in vitro digestibility of wheat starch (WS). Results from rapid viscosity analysis (RVA) and low-field nuclear magnetic resonance (LF-NMR) analysis revealed that GMs with lower branching degrees were correlated with higher paste viscosity, peak viscosity, and greater water-holding capacity in the WS-GM mixtures. Additionally, these lower branching GMs more effectively inhibited amylose leaching during starch gelatinization, leading to a softer gel texture and increased transparency of the mixtures. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis demonstrated that starch mixtures containing lower branching GMs exhibited reduced relative crystallinity and enthalpy values during aging. Furthermore, the incorporation of lower branching GMs resulted in decreased starch digestibility in vitro, thereby enhanced resistant starch content. These findings highlight the potential of selectively branched GMs to modulate the functional properties and nutritional profile of WS, providing a promising approach for the development of starch-based products with improved health benefits.

Structural changes of wheat starch and activity inhibition of α-glucosidase by persimmon (Diospyros kaki Thunb.) leaves extract retarding starch digestibility

Elevated blood sugar levels caused by starch digestion was a target for controlling diabetes mellitus. The in vitro and in vivo digestibility of wheat starch was evaluated to find that adding 15 % persimmon leaf extract (PLE) to starch reduced its digestibility by 69.50 % and the peak postprandial blood glucose by 23.63 %. Subsequently, we observed under scanning electron microscopy and atomic force microscopy that the presence of PLE led to the destruction of starch structure and the aggregation of α-glucosidase so as to decrease starch digestion and hinder the binding of starch to α-glucosidase. Through multi-spectral analysis, PLE hindered the clathrate of iodine and starch, and also increased the crystallinity of starch by 48.58 %. For α-glucosidase inhibitory activity (IC50 = 72.49 μg/mL), PLE preferentially occupied the active center of α-glucosidase, changed its fluorescence characteristics and secondary structure through hydrogen bonding and hydrophobic interaction. Moreover, among the 23 potential α-glucosidase inhibitors screened from PLE, combined with molecular simulation, Procyanidin B2 had the strongest inhibitory effect (IC50 = 33.22 μg/mL) and binding energy (−7.09 kcal/mol), which was most effectively inhibitory on digestion. These results indicated the potential of PLE in hypoglycemia targeting both starch and α-glucosidase.

Understanding the influence of β-glucan-based superabsorbent hydrogel on the digestibility of wheat starch: Gelatinization, rheological and structural properties

This study aims to evaluate the effects of β-glucan-based superabsorbent hydrogel (βCHY) on wheat starch digestibility and elucidate the underlying mechanism. The results revealed that the incorporation of βCHY led to a significant reduction in rapidly digestible starch content of wheat starch from 71% to 44%, while concurrently increasing the levels of slowly digestible starch and resistant starch in a dose-dependent manner. From a mechanistic perspective, incorporating βCHY into wheat starch notably affected their pasting behavior and influenced the rheological properties and gel strength of resulting gels. Moreover, the addition of βCHY increased the relative crystallinity, short-range ordered degree (R1047/1024), molecular order (the full width at half maximum at 480 cm−1), and thermal stability of the starch, suggesting the formation of a more stable and ordered structure. Furthermore, the wheat starch-βCHY gel complexes exhibited large, discrete layered structures with thicker layer walls, accompanied by interspersed filament-like structures. These structural alterations may collectively contribute to the reduced digestibility of wheat starch. These findings confirmed the positive effects of βCHY on the starch digestibility, offering valuable insights into the development of innovative starch-based foods with slow digestion characteristics.

Gluten fractions unevenly altered the digestion and physical properties of wheat starch‐lauric acid system under non‐alkaline/alkaline conditions

SummaryThis research delved into the role of gluten fractions on digestion, physical properties and structure of wheat starch (WS)–lauric acid (LA) system under non‐alkaline/alkaline conditions. Results showed that gluten fractions decreased the digestion of WS with LA and gliadin had greater effect on the digestion of WS with LA under non‐alkaline/alkaline conditions than glutenin. Specifically, gliadin increased RS content of WS with LA by 70.99% and 84.89%, respectively, under non‐alkaline and alkaline conditions. The diminished in WS digestion caused by gluten fractions and LA ascribed to the decrease in swelling power and leaching of starch. Rapid viscosity analyser (RVA) demonstrated that gluten fractions were conducive to WS–LA and/or WS–LA–protein complexes formation and gliadin was more helpful to these complexes' formation than glutenin under non‐alkaline conditions. Additionally, gliadin had greater effect on the stability and short‐range ordered structure of WS with LA than glutenin. Addition of gliadin resulted in 6.79% and 13.33% of increase in short‐range orderliness compared with WS–LA system under non‐alkaline and alkaline conditions, respectively. Furthermore, gluten fractions had greater influence on the digestion of WS with LA under alkaline conditions than non‐alkaline conditions ascribed to the formation of WS–LA and/or WS–LA–protein complexes with low swelling power and high ordered structure under alkaline conditions. This study provided crucial information on the design of starchy foods with low digestion.

Impact of Esterification with Octenyl Succinic Anhydride on the Structural Characteristics and Glucose Response in Mice of Wheat Starch.

In this study, we investigated the structural properties and digestibility of wheat starch treated with octenyl succinic anhydride (OSA). For the experiment, the samples were reacted with 2, 4, 6, 8, and 10% OSA (pH 8.5-9.0) for 2 h. A light micrograph showed that there was no difference in the morphology and Maltese cross between native and OSA-treated starch. The X-ray diffraction (XRD) patterns of the native and OSA-treated starches showed typical A-type diffraction. In addition, the Fourier transform infrared (FT-IR) spectrum showed a distinct carbonyl peak at approximately 1730 cm-1, indicating the stretching vibration of the C=O bond of the ester group. The degree of substitution (DS) and content of resistant starch (RS) increased with increasing concentrations of treated OSA because of the increase in ester bonds. In particular, RS was thermostable compared to the RS content in uncooked and cooked starch. Blood glucose levels and response in vivo decreased as the OSA concentration increased. Treatment of wheat starch with 8% OSA concentration produced 35.6% heat-stable resistant starch. These results suggest that starch modified with OSA can be used to produce functional foods for diabetes.

Effects of Kiwifruit Dietary Fibers on Pasting Properties and In Vitro Starch Digestibility of Wheat Starch.

In this study, the roles of kiwifruit soluble/insoluble dietary fiber (SDF/IDF, respectively) in the pasting characteristics and in vitro digestibility of wheat starch were explored. According to RVA and rheological tests, the IDF enhanced the wheat starch viscosity, decreased the gelatinization degree of the starch granules, and exacerbated starch retrogradation. The addition of SDF in high quantities could reduce the starch gelatinization level, lower the system viscosity, and exacerbate starch retrogradation. Through determining the leached amylose content and conducing scanning electron microscopy, the IDF and SDF added in high quantities was combined with the leached amylose wrapped around the starch granules, which reduced the leached amylose content and decreased the gelatinization degree of the starch granules. The Fourier transform infrared results showed that the addition of both the IDF and SDF resulted in an enhancement in hydrogen bonding formed by the hydroxyl groups of the system. The in vitro digestion results strongly suggested that both the IDF and SDF reduced the wheat starch digestibility. The above findings are instructive for the application of both IDF and SDF in starchy functional foods.

The structure and in vitro starch digestibility of wheat starch-glycerol monopalmitin complexes: the effect of heating conditions and water content

The effects of the heating conditions and water content on the structure and digestibility of wheat starch (WS)-glycerol monopalmitin (GMP) complexes were investigated. The results showed that the higher water content and the heating conditions of 90°C for 60 min after 100°C for 10 min favor the formation of more WS-GMP complexes with the greater short-range order, although the thermal transition temperatures of GWS-GMP-100 complexes are not significantly affected by the water content. Only the type I complexes were formed under the heating conditions of 90°C for 60 min. The heating conditions of 90°C for 60 min after 100°C for 10 min facilitates the formation of type II complexes, and the amounts of type II complexes increased with increasing water content. The digestion rates of WS-GMP complexes decreased slightly with increasing water content, and the extent of starch amylolysis of WS-GMP complexes significantly decreased after heating further at 90°C compared with that only heating at 100°C. The digestibility of complexes is mainly related to structural order rather than the number of complexes. This study is helpful to further understand starch-lipid complexes by showing that heating conditions and water content influence the formation of WS-GMP complexes.

Effect of mulberry leaf polysaccharides on the physicochemical, rheological, microstructure properties and in vitro starch digestibility of wheat starch during the freeze-thaw cycles

Temperature fluctuation damages the quality of starch-based foods, and the freeze-thaw cycle (FTC) can simulate this process. This study investigated how Mulberry leaf polysaccharides (MLP) affect the freeze-thaw stability and digestibility of wheat starch (WS). During FTC, MLP reduced the syneresis and retarded the water migration of WS gel. Meanwhile, MLP delayed the recrystallization of starch, which reduced the enthalpy value and crystallinity of WS gel during FTC. The addition of MLP significantly reduced the hardness of WS gel. Furthermore, MLP could prevent the deterioration of the rheological characteristic and preserve the network structure of the WS gel. In addition, MLP boosted the resistant starch and decreased the fast-digesting starch content in the freeze-thaw gel. Our findings suggested that MLP could enhance the freeze-thaw stability of WS gel, decrease the starch digestibility, and be an effective component in improving the quality of wheat starch-based frozen food.

Study on the mechanism of various exogenous proteins with different inhibitions on wheat starch digestion: From the distribution behaviors of protein in the starch matrix

This study aimed to compare the effect of various exogenous proteins on wheat starch (WS) digestion and assess the relevant mechanisms based on the distribution behaviors of exogenous proteins in the starch matrix. Rice protein (RP), soy protein isolate (SPI), and whey protein isolate (WPI) all effectively suppressed the rapid digestion of WS but with different modes. RP increased the slowly digestible starch content, while SPI and WPI increased the resistant starch content. Fluorescence images showed that RP aggregated and competed for effective space with starch granules, while SPI and WPI formed continuous network structures among the starch matrix. These distribution behaviors endowed different reductions in starch digestion by influencing the gelatinization and ordered structure of starch. Pasting and water mobility results suggested all exogenous proteins inhibited the water migration and swelling of starch. Simultaneously, X-ray diffraction and Fourier transform infrared spectroscopy analysis showed that exogenous proteins improved the ordered structures of starch. RP had a more significant effect on the long-term ordered structure, while SPI and WPI had a more effective effect on the short-term ordered structure. These findings will enrich the theory of exogenous protein inhibiting starch digestion and inspire the applications in low-glycemic index food.

Determining whether granule structural or surface features govern the wheat starch digestion, a kinetic analysis

Deciphering the determinants of starch digestion from multiple interrelated properties is a challenge that can benefit from multifactorial data analysis. The present study investigated the digestion kinetic parameters (rate, final extent) of size-fractions from four commercial wheat starches with different amylose contents. Each size-fraction was isolated and characterized comprehensively using a large range of analytic techniques (FACE, XRD, CP-MAS NMR, time-domain NMR, DSC…). A statistical clustering analysis applied on the results revealed that the mobility of water and starch protons measured by time-domain NMR was consistently related to the macromolecular composition of the glucan chains and to the ultrastructure of the granule. The final extent of starch digestion was determined by the granule structural features. The digestion rate coefficient dependencies, on the other hand, changed significantly with the range of granule size, i.e. the accessible surface for initial binding of α-amylase. The study particularly showed the molecular order and the chains mobility predominantly limiting or accelerating the digestion rate depending on the accessible surface. This result confirmed the need to differentiate between the surface and the inner-granule related mechanisms in starch digestion studies.

Understanding the digestibility of wheat starch- caffeic acid complexes prepared by hot-extrusion 3D printing technology

In this study, WS-CA complexes were prepared with wheat starch (WS) and caffeic acid (CA) by the hot-extrusion 3D printing (HE-3DP) technology. In vitro digestion experiment was performed to investigate the effects of CA on WS digestibility. Moreover, the effects of CA on WS structures as well as amylase activities (both α-amylase and α-glucosidase) were studied by X-ray diffraction, multi-spectroscopy, and molecular simulation methods. The results of in vitro digestion showed that digestibility of WS-CA complexes decreased significantly compared to that of WS. FT-IR spectroscopy and X-ray diffraction demonstrated that CA and WS formed a highly ordered B + V-type crystalline structure by hydrogen bonding. According to the enzyme inhibition kinetic results, CA was able to inhibit α-amylase (PPA) and α-glucosidase (SCG) activities in a competitive-type manner and mixed-type manner, respectively. Molecular modelling results showed that CA mainly bound to Asp197 at the active sites of PPA and Asp233 at the hydrophobic cavity of SCG, which could increase amylase's structural rigidity and prevent WS from contacting enzymes. The results of logarithm-of-slope model suggested that CA could change WS structures, inhibit amylase activities and reduce WS digestibility under the synergistic effects. These findings could offer valuable information on CA reducing starch digestibility by the HE-3DP technology.

Arabinoxylan of varied structural features distinctively affects the functional and in vitro digestibility of wheat starch

This study explored the effects of wheat bran arabinoxylan (AX) of various molecular structures on the functional and in vitro digestibility of wheat starch. AX was separated with sequential ethanol precipitation into different fractions (L-Fra and H-Fra), followed by acidic treatment at varied time to convert L-Fra into different subfractions (H-Sub, M-Sub and L-Sub), and the structural features of AX and its subsequent fractions were compared. The Mw and branching degree of the fractions were decreased in the order of H-Fra (545 kDa, 1.15), L-Fra (86 kDa, 0.35), H-Sub (38 kDa, 0.16), M-Sub (21 kDa, 0.10) and L-Sub (7 kDa, 0.08). The functional properties, such as pasting properties, rheological properties, thermal properties, and their effect on the in vitro digestibility of wheat starch-AX combinations, were closely related to the molecular structures of AX. AX with higher Mw, higher branching degree and phenolic content could better inhibit the starch gelatinization and retrogradation, thus reducing the apparent viscosity and gelling properties of wheat starch. The possible mechanisms can be illustrated as 1) AX could compete for water with starch to inhibit granule expansion; 2) AX could not only adsorb on the surface of starch granules through hydrogen bonds but also entangle with the leached amylose and wrap on the surface of granules; 3) AX contained phenols, leading them to inhibit granule expansion through non-covalent interactions with starch molecules. Overall, this study provides a theoretical basis to improve the quality of wheat starch foods and extend the shelf life of wheat foods.

Effects of laminarin on the structural properties and in vitro digestion of wheat starch and its application in noodles

In this study, wheat starch (WS) was combined with different concentrations of laminarin (LM) to investigate changes in its microstructure, structure and digestibility. The application of LM to improve the cooking and textural properties of wheat noodles was also investigated. A low concentration of LM (2%, g/100g) reduced the crystallinity and order degree of WS, but a high concentration had the opposite effect. After LM addition, the leached amylose content and swelling power of WS were significantly reduced, indicating that LM coats the starch granule surface, inhibiting swelling and reducing amylose leaching. The addition of LM also significantly changed the microstructure of WS; WS granules aggregated in the presence of LM, forming a denser structure. In vitro digestion indicated that LM strongly inhibits the digestibility of WS, with 6% LM (g/100g) having the strongest inhibitory effect. Cooking and textural analysis of noodles showed that the addition of LM could improve the textural quality of noodles, by reducing cooking loss, increasing water absorption and hardness, and reducing adhesiveness.

Synergistic effect of endogenous gluten and oleic acid on wheat starch digestion by forming ordered starch-fatty acid-protein complexes during thermal processing

The aim of this study was to understand the potential of endogenous gluten inhibiting the digestibility in vitro of wheat starch (WS) in starch-fatty acid-protein system. Therefore, the influences of gluten and whey protein isolate (WPI) on the properties, multi-scale structure and in vitro digestibility of WS in WS-oleic acid (OA)-protein system were compared. The results of digestibility in vitro indicated that the ternary system of starch-fatty acid-protein showed higher resistant starch (RS) content as well as lower rapidly digestible starch (RDS) content than the binary system of WS-OA, demonstrating protein decreased WS digestion of WS-OA system. The results of pasting properties showed that gluten and WPI both increased the viscosities of WS-OA system during the cooling period due to the formation of WS-OA-protein ternary complex. The results of swelling power and solubility analysis showed that gluten and WPI both decreased the swelling power and solubility of WS-OA binary system. Laser Confocal Raman and X-ray diffraction (XRD) studies indicated that gluten and WPI both increased the ordered degree of WS-OA binary system by decreasing the full width at half maximum (FWHM) of the peak at 480 cm−1 and increasing crystallinity degree. Strikingly, compared with WPI, gluten had greater effects on the digestibility in vitro, pasting properties and ordered degree of WS in WS-OA-protein system. Therefore, gluten as an endogenous protein has the potential application in reduction the enzymatic digestibility of WS by regulating the reassembly of starch and fatty acid during thermal processing.

Extraction, purification, structural characterization of Anemarrhena asphodeloides polysaccharide and its effect on gelatinization and digestion of wheat starch

Pressurized water extraction (PWE) of the polysaccharides from Anemarrhena asphodeloides rhizomes was optimized by the response surface method (RSM). The high yield of 34.82 ± 0.38% was gained under the optimal conditions of material to liquid ratio 42 mL/g, pressure 6.4 MPa, extraction temperature 51 °C, and extraction time 15.3 min. An Anemarrhena asphodeloides rhizome polysaccharide (AARP) was obtained after purifying by D4006 macroporous resin and Sephadex G-100 column. High-performance liquid chromatography (HPLC) analysis showed that AARP with the molecular weight of 5100 Da consisted of four monosaccharides including mannose, glucose, galactose, and arabinose. 1D and 2D NMR analyses confirmed that the backbone of AARP was comprised of →4)-β- D -Man p -(1→, →4)-β- D -Glc p -(1→, β- L -Ara f -(1→, →2)-β- D -Man p -(1→, and →3)-α- D -Gal p -(1→ residues. In addition, AARP exhibited the property of inhibiting the pasting and in vitro digestion of wheat starch. These findings laid the foundations for AARP as an additive in regulating starch foods. • Pressurized water extraction was an efficient method to extract Anemarrhena asphodeloides polysaccharide. • A new neutral polysaccharide (AARP) containing four monosaccharides was obtained. • The primary structure of AARP was determined by Chemical methods and instrument analysis. • AARP could effectively inhibit the pasting and in vitro digestion of wheat starch.

The impact of the soluble protein fraction and kernel hardness on wheat flour starch digestibility

Wheat is the staple crop for 35% of the world’s population, providing a major source of calories, mainly in the form of starch. The digestibility of wheat starch varies between different flours and products. Wheat products that are rapidly digested elicit large post-prandial glucose peaks associated with metabolic disorders. We investigated the impact of protein on starch digestion in three commercial flours with different grain hardness. A soluble extract of wheat proteins reduced starch digestion, even following gastric proteolysis. This extract was enriched in proteinaceous α-amylase inhibitors which were partially degraded during gastric proteolysis. Starch digestion kinetic analysis was carried out for flour samples pre-treated with different pepsin activities. The rate of starch digestion was altered following pepsin pre-digestion, and the extent of starch digestion increased in response to pepsin pre-digestion. We conclude that soluble proteinaceous alpha-amylase inhibitors present in wheat can escape gastric digestion and significantly contribute to reducing starch digestion in the small intestine.

Preliminary Study on the Influence of the Polyphenols of Different Groups on the Digestibility of Wheat Starch, Measured by the Content of Resistant Starch

The scientific goals of this research were to examine the impact of various polyphenols from different groups on resistant starch development. Wheat starch was tested, and the polyphenols were added to starch after its pasting in the amount suggested in the literature as optimal—10 mg, and at twice and half the optimal, i.e., 20 mg and 5 mg. The most frequently consumed and most frequently occurring compounds in food products were selected for the proposed research: (1) phenolic acids—p-coumaric acid, ferulic acid; (2) flavanones—hesperidin, naringenin; (3) flavanols—(+)catechin, epigallocatechin gallate; (4) flavonols—quercetin, kaempferol; (5) anthocyanins—cyanidin-3-O-glucoside, delphinidin-3-O-glucoside. As a result, either the dose or the kind of polyphenolic compound had a statistically significant influence on the wheat starch digestibility (p < 0.05). However the observed impact was dose-dependent, and interestingly, higher amounts of RS were found in the case of the lowest dose applied (5 mg—4.76% of starch gel; mean = 2.94 ± 1.23 g·100 g−1 dm) as compared to the other doses: 10 mg—9.09% of starch gel (mean = 1.58 g·100 g−1 dm) and 20 mg—16.66% of starch gel (mean = 1.51 ± 0.90 g·100 g−1 dm). Among all tested polyphenols added to wheat starch gels in an amount of 10 mg and 20 mg, epigallocatechin gallate was found to be the most effective compound (p < 0.05), while (+)catechin was most efficient in the dose of 5 mg (p < 0.05).

Antioxidant potential and in vitro inhibition of starch digestion of flavonoids from Crataegus pinnatifida

Hawthorn flavonoids were extracted by enzymolysis associated ultrasonic procedure. Thirteen flavonoids were identified by HPLC/ESI-QTOF/MS, and the major components were procyanidin C1, rutin-rhamnoside, vitexin-rhamnoside, and catechin. Hawthorn flavonoids exhibited strong free radical scavenging activities against DPPH, ABTS, and hydroxyl radicals. Total and intercellular antioxidant experiments revealed that the free hydro-PSC value was 295.32 ± 12.20 μmol of VCE/g DW, and the free cellular antioxidant activity (CAA) values were 168.60 ± 4.87 μmol of QE/g DW in the no PBS wash protocol and 49.53 ± 1.75 μmol of QE/g DW in the PBS wash protocol. In addition, hawthorn flavonoids exhibited higher α-amylase and α-glucosidase inhibitory activities. The wheat starch digestibility was also reduced by hawthorn flavonoids as well. The results indicated that enzymolysis associated ultrasonic extraction was advisable for extracting flavonoids from hawthorn, and hawthorn flavonoids might be recommended as a potential food supplement with hypoglycemic activities.

Mechanism governing the rice glutelin fibrils on inhibition of in vitro wheat starch digestion

Our previous research found that rice glutelin fibril aggregates (RGFA) can mitigate in vitro starch digestion, while the mechanism is not well understood. Here the effects of RGFA on starch properties and activities of amylolytic enzymes were studied. The peak viscosity decreased significantly to 1041.0 ± 11.3 cP (mixture of 10 h fibril and starch) ( p < 0.05). The short-range structural order of starch (R-value, calculated from the intensity ratio of the bands at 1047 and 1022 cm −1 ) changed from 0.73 ± 0.02 (pure wheat starch) to 0.86 ± 0.01 (mixture of 2 h fibril and starch), and 0.58 ± 0.01 (mixture of 10 h fibril and starch) ( p < 0.05). The RGFA inhibited in vitro wheat starch digestion significantly ( p < 0.05). And RGFA also displayed strong inhibitory effects on amylolytic enzymes. The residual activities of α-amylase, glucosidase and double enzymes were only 61.0 ± 3.2, 63.1 ± 2.5, and 60.5 ± 0.1%, respectively in the presence of 2 h fibril. The results indicated that RGFA with distinctly different fibril structures had different inhibitory mechanisms on starch digestion. The study provides new strategies for application of food protein fibrils and production of foods with reduced starch digestion. • Rice glutelin fibril aggregates (RGFA) may inhibit starch from gelatinization. • h fibril displayed the highest inhibition effect on α-amylase activity. • RGFA with distinct structure had different inhibitory mechanism on starch digestion. • The study provides new strategies for application of food protein fibrils.