Effects of heat treatment on protein molecular structure and in vitro digestion in whole soybeans with different moisture content

Effects of germination on the digestibility of instant soybean powders based on an in vitro digestion model of the aged static gastrointestinal tract

Germination and heat processing can improve the digestibility of soybean protein, so for the elderly and people with gastrointestinal dysfunction, instant soybean powder is an ideal source for protein intake. In this study, the changes in protein and anti-nutritional factors in the instant germinating soybean powders were investigated systematically, and the aged gastrointestinal digestion model analyzed the digestive characteristics of instant germinating soybean powders. The results showed that during processing, particle size, disulfide bond, and β-sheets decreased, free sulfhydryl and α-helix increased. The change resulted in the decrease of proteolysis degree and particle size of gastrointestinal digestive products, and the increase of surface hydrophobic index. At the same time, anti-nutritional factors decreased by about 30 % to 60 %. The above reasons are combined with the protein digestibility of S72 5.88 % higher than Y0. This study proved that instant soybean powder is more conducive to the digestion and absorption of the elderly.

Structural basis for the effects of thermal treatment on soybean seed β-conglycinin

The production of soy protein in the food industry is inextricably linked to the thermal sterilization process. To gain a deeper understanding of the changes in protein structure during this process, we compared the structural effects of typical thermal sterilization methods (pasteurization and ultra-high temperature sterilization) on β-conglycinin. Chemical characterization of the solutions showed that two thermal sterilization methods did not affect the primary structure and overall morphology of β-conglycinin. However, the α-helix and β-sheet content were reduced. Additionally, the crystal structure of β-conglycinin after different heat treatments was successfully determined by X-ray crystallography. Notably, we precisely observed the sites where the secondary structure was altered at the atomic level. This allowed us to propose a hypothesis that the highly variable continuous antiparallel β-sheet within the C-terminal core β-barrel structural domains may represent an intermediate state influenced by temperature, acting as the initiation site for protein structure dissociation.

Current insights into heat treatment for improving functionalities of soy protein: A review

Nowadays, soy protein-based food is consumed globally as an eco-friendly and healthy plant-based alterative. Nevertheless, more effort is still needed to improve the functionalities of soy protein for a wider application and addressing its existing challenges. Heat treatment is a fundamental approach in industrial food processing due to its simplicity, cost-effectiveness, and versatility. This review gave an emphasis on the recent advance in improving the functionalities of soy protein by heat treatment, including traditional and innovative heating, as well as a combination of heating and other techniques. Traditional thermal treatment has been proven to effectively improve the techno-functional properties of soy protein (e.g., heat stability; emulsifying, foaming, and gelation properties; and fibrillation), or to overcome its drawbacks (e.g., nutritional issues and antigenicity), or to promote its interactions with other compounds for novel functionalities via complicated protein changes (including conformational changes (e.g., unfolding, secondary and tertiary structures, surface hydrophobicity/charge) and covalent and/or non-covalent aggregation, as well as binding with other compounds). Recently, researchers have also proposed innovative heating and combination of heating and other techniques for a more efficient and effective soy protein modification. This review gave hints for a more precise and tailored modulation of soy protein functionalities via heat treatment in the commercial application.

Understanding the structural differences in chickpea globulins and their relationship with in vitro protein digestibility

The relationship between structural protein differences and changes in legumin, vicilin, and chickpea globulin during digestion and protein digestibility has not yet been fully explored. In this study, we characterized the conformational properties and the secondary structures of chickpea protein isolates (globulin), legumin, and vicilin before and after in vitro digestion to understand their roles in protein digestibility. The globulins were characterized by size, surface charge, hydrophobicity, sulfhydryl group content, and solubility. Protein hydrolysis was determined by the OPA method and electrophoresis. The structural changes were elucidated using FTIR spectroscopy. Vicilin had a bimodal particle size distribution and high polydispersity, indicating more heterogeneous particles with lower surface hydrophobicity, fewer free SH groups, and higher solubility (62%) than those of legumin and globulin. Turbidity was correlated with the aggregation index, with legumin exhibiting the highest value. During the gastric phase, in contrast to legumin (34.2%) and vicilin (31.4%), the protein hydrolysis was the highest in globulin fraction (42.2%). However, at the intestinal level, vicilin exhibited highly digested proteins (99%), as confirmed by SDS-PAGE. FTIR analysis demonstrated differences in secondary structure changes between vicilin with an increase in random coils (22%) and globulin and legumin, which displayed highly parallel β-sheet structures (28.7% and 26%, respectively). These results highlight the importance of conformational switching in the secondary structure of globulins for protein digestibility. Promoting unorganized secondary structures, high solubility, and low aggregation improves globulin protein digestibility. Examination of the structure and digestion of chickpea globulins provides valuable information for the development of plant-based products.

The structure-function relationships and techno-functions of β-conglycinin

β-conglycinin (β-CG) is a prominent storage protein belonging to the globulin family in soybean (Glycine max) seeds. Along with other soybean proteins, it serves as an important source of essential amino acids and high-quality nutrition. However, the digestibility and nutritional value of β-CG are key factors affecting the nutritional profile of soy-based foods. The heterotrimeric, secondary, and quaternary structures of β-CG, particularly the spatial arrangement of its α, α', and β subunits, influence its functional properties. Considering these aspects, β-CG emerges as a significant protein with diverse applications in the food and health sectors. Therefore, this review explores β-CG's composition, structure, function, health implications, and industrial uses. Salient discussions are presented on its molecular structure, nutrition, digestibility, allergenicity, and techno-functions including emulsification, solubility, gelling, and structure-function complexities. Overall, the multifaceted potential of β-CG in the healthcare sector and the food industry is evident.

Soy proteins modified using cavitation jet technology

Soy proteins are seen as a promising alternative food source for meat with environmentally friendly properties. The problem is that the functional properties of soy proteins do not meet the needs of the food industry, and some existing modification technologies have adverse effects. Recently, cavitation jet technology (CJT) has been studied because it generates high heat, high pressure, strong shear and strong shock waves. This review summarizes the history and mechanism of cavitation jets. The energy generated during the cavitation jet process can open molecular structures, and the shock waves and microjets generated can pulverize the materials by erosion. The impact of the CJT on the morphology, structure, and functionality of soy proteins is discussed. The impact of combining CJT with other techniques on the production of soy proteins was also reviewed. The modification of proteins using two or more methods with complementary strengths, avoiding the disadvantages of certain techniques, makes the modification of proteins more effective. One of the most prominent effects is the combined treatment of cavitation jets with physical techniques. Finally, the review provides a comprehensive analysis of the application of modified soy proteins in the food industry and highlights promising avenues for future research.

Fabrication, characterization, and in vitro digestion of gelatin/gluten oleogels from thermally crosslinked electrospun short fiber aerogel templates

In this work, the electrospun short fiber-based oleogels (ESFO) were formed by thermal crosslinking. Gelatin and gluten nanofibers were obtained via electrospinning, then homogenized and transformed into short fiber dispersions. Through freeze-drying, electrospun short fiber-based aerogel (ESF-A) templates were obtained for oil adsorption. All ESF-A exhibited the micromorphology of loose fibrous pore structure and prominent changes of characteristic peaks in the thermal and infrared analyses. Moreover, the highly crosslinked templates owned excellent hydrophobicity and mechanical performances (elastic modulus: 0.25 kPa, yield strength: 14.56 kPa, compressive strength: 52.54 kPa, and the final compression recovery: 91.27%). Meanwhile, the oil adsorption/oil holding capacity could reach 76.56 g/g and 80.04%, respectively. Through thermal crosslinking, ESF-O presented good and controllable rheological/in vitro digestion properties, which were further confirmed by PCA analysis. According to different application conditions, ESF-O properties could be adjusted by different degrees of fiber addition or thermal crosslinking.

Impact of Simultaneous Nutrient Priming and Biopriming on Soybean Seed Quality and Health

In soybean production, numerous strategies are utilized to enhance seed quality and mitigate the effects of biotic and abiotic stressors. Zn-based nutrient priming has been shown to be effective for field crops, and biopriming is a strategy that is becoming increasingly important for sustainable agriculture. On the other hand, there is a lack of information about the effect of comprehensive nutrient priming and biopriming techniques on soybean seed quality and viability and seed health. This study was performed to assess the benefits of nutrient priming with Zn, biopriming with Bacillus megaterium and Bradyrhizobium japonicum (single and co-inoculation), and combination of nutrient priming and biopriming on the seed quality and viability, as well as seed infection caused by Alternaria spp. and Fusarium spp. Three different laboratory tests were employed: germination test, accelerated aging test, and seed health test. The results revealed that all tested priming treatments have a beneficial effect on seed germination, initial plant growth, and reduction of seed infection in normal and aged seeds. Additionally, comprehensive priming with Zn, Bacillus megaterium, and Bradyrhizobium japonicum reduced the occurrence of Alternaria spp. (-84% and -75%) and Fusarium spp. (-91% and -88%) on soybean seeds in the germination and accelerated aging tests, respectively, as compared to the control, which proved to be the most effective treatment in both optimal and stressful conditions.

Effect of Germination on the Digestion of Legume Proteins

As one of the main sources of plant protein, it is important to improve the protein digestibility of legumes. Faced with population growth and increasing environmental pressures, it is essential to find a green approach. Germination meets this requirement, and in the process of natural growth, some enzymes are activated to make dynamic changes in the protein itself; at the same time, other substances (especially anti-nutrient factors) can also be degraded by enzymes or their properties (water solubility, etc.), thereby reducing the binding with protein, and finally improving the protein digestibility of beans under the combined influence of these factors The whole process is low-carbon, environmentally friendly and safe. Therefore, this paper summarizes this process to provide a reference for the subsequent development of soybean functional food, especially the germination of soybean functional food.

Quercetin Supplementation Improves Intestinal Digestive and Absorptive Functions and Microbiota in Rats Fed Protein-Oxidized Soybean Meal: Transcriptomics and Microbiomics Insights

To clarify the nutritional mechanisms of quercetin mitigation in the digestive and absorptive functions in rats fed protein-oxidized soybean meal, 48 three-week-old male SD rats were randomly allocated into a 2 × 2 factorial design with two soybean meal types (fresh soybean meal or protein-oxidized soybean meal) and two quercetin levels (0 or 400 mg/kg) for a 28-day feeding trial. The protein-oxidized soybean meal treatment decreased (p < 0.05) the relative weights of the pancreas, stomach, and cecum, duodenal villus height, pancreatic and jejunal lipase activities, apparent ileal digestibility of amino acids, and apparent total tract digestibility of dry matter, crude protein, and ether extract. The supplementation of quercetin in the protein-oxidized soybean meal diet reversed (p < 0.05) the decreases in the duodenal length, ileal villus height, lipase activity, apparent ileal digestibility of amino acids, and apparent total tract digestibility of dry matter, crude protein, and ether extract. Transcriptomics revealed that the "alanine transport" and "lipid digestion and absorption" pathways were downregulated by the protein-oxidized soybean meal compared with fresh soybean meal, while the "basic amino acid transmembrane transporter activity" and "lipid digestion and absorption" pathways were upregulated by the quercetin supplementation. Microbiomics revealed that the protein-oxidized soybean meal increased the protein-degrading and inflammation-triggering bacteria in the cecum, while the relative abundances of beneficial bacteria were elevated by the quercetin supplementation.

Effect of dry- and moist-heat treatment processes on the structure, solubility, and in vitro digestion of macadamia protein isolate

This study aimed to enhance the solubility and digestibility of macadamia protein isolate (MPI) for potential utilization in the food industry. The impact of dry- and moist-heat treatments at various temperatures (80, 90, and 100°C) and durations (15 and 30 min) on macadamia protein's microstructure, solubility, molecular weight, secondary and tertiary structure, thermal stability, and digestibility were investigated and evaluated. The heating degree was found to cause roughening of the MPI surface. The solubility of MPI after dry-heat treatment for 15 min at 100°C reached 290.96 ± 2.80% relative to that of untreated protein. Following heat treatment, the bands of protein macromolecules disappeared, while MPI was stretched by vibrations of free and hydrogen-bonded hydroxyl groups. Additionally, an increase in thermal stability was observed. After heat treatment, hydrophobic groups inside the protein are exposed. Heat treatment significantly improved the in vitro digestibility of MPI, reaching twice that of untreated protein. The results also demonstrated that dry- and moist-heat treatments have distinct impacts on MPI, while heating temperature and duration affect the degree of modification. With a decreased ordered structure and increased random coil content, the dry-heat treatment significantly enhanced the in vitro digestibility of MPI. The digestibility of MPI after dry-heat treatment for 30 min at 90°C increased by 77.82 ± 2.80% compared to untreated protein. Consequently, compared to moist-heat treatment, dry-heat treatment was more effective in modifying macadamia protein. Dry-heat treatment of 30 min at 90°C was determined as the optimal condition. PRACTICAL APPLICATION: Heat treatment enhances MPI characteristics, potentially advancing macadamia-derived food production, including plant-based beverages and protein supplements.

A comprehensive evaluation of milk protein molecular weight distribution based on exclusion chromatography dataset

Molecular weight is one of the main characteristic parameters of proteins, which is the basis for the functional properties of milk protein. This research aims at establishing molecular weight distribution pattern of milk protein based on exclusion chromatography. The method selected Na3PO4-Na2SO4 (0.1 M, pH 6.7) buffer as the mobile phase and detected at 220 nm by HPLC-UV. The protein molecular weight distributions were determined and compared for human milk, bovine milk, and infant formula. The proportion of macromolecular proteins is much higher in infant formula compared to human or bovine milk. The protein molecular weights of human and bovine milk are significantly different around 90, 20, 14, and 2 kDa. The results provide holistic compare of bovine milk, human milk, and infant formula through protein molecular distribution. The new evaluation indicators for protein will drive technological simulation of infant formula.

Plant-based proteins: advances in their sources, digestive profiles in vitro and potential health benefits

Plant-based proteins (PBPs), which are environmentally friendly and sustainable sources of nutrition, can address the emerging challenges facing the global food supply due to the rapidly increasing population. PBPs have received much attention in recent decades as a result of high nutritional values, good functional properties, and potential health effects. This review aims to summarize the nutritional, functional and digestive profiles of PBPs, the health effects of their hydrolysates, as well as processing methods to improve the digestibility of PBPs. The diversity of plant protein sources plays an important role in improving the PBPs quality. Several types of models such as in vitro (the static and semi-dynamic INFOGEST) and in silico models have been proposed and used in simulating the digestion of PBPs. Processing methods including germination, fermentation, thermal and non-thermal treatment can be applied to improve the digestibility of PBPs. PBPs and their hydrolysates show potential health effects including antioxidant, anti-inflammatory, anti-diabetic, anti-hypertensive and anti-cancer activities. Based on the literature, diverse PBPs are ideal protein sources, and exhibit favorable digestive properties and health benefits that could be further improved by different processing technologies. Future research should explore the molecular mechanisms underlying the bioactivity of PBPs and their hydrolysates.

Wheat bran arabinoxylan-soybean protein isolate emulsion-filled gels as a β-carotene delivery carrier: Effect of polysaccharide content on textural and rheological properties

This study aimed to investigate the effects of different wheat bran arabinoxylan (WBAX) concentrations (1, 2, 3, and 4 wt%) on the structural and physicochemical properties of WBAX-soybean protein isolate (SPI) emulsion-filled gels (EFGs) prepared using laccase and heat treatment. The properties of the various gels as well as their microstructure, rheology, and in vitro digestion behaviors were investigated. Results showed that WBAX-SPI EFGs with a 3 wt% WBAX concentration had a smooth and uniform appearance, high water holding capacity (98.5 ± 0.2 %), and enhanced mechanical properties. Rheological experiments suggested that a stronger and closer gel network was formed at 3 wt% WBAX concentration. Fourier transform infrared spectroscopy showed that laccase and heat treatment not only catalyzed the intramolecular crosslinking of WBAX and SPI, respectively, but also promoted the interaction between WBAX and SPI. Confocal laser scanning microscopy revealed that the WBAX gel network was interspersed within the SPI network. The interactions contributing to the gelation analysis revealed that chemical (disulfide bond) and physical (hydrogen bond and hydrophobic) interactions promoted the formation of denser EFGs. Furthermore, the WBAX-SPI EFGs provided a β-carotene bioaccessibility of 21.8 ± 0.6 %. Therefore, our study suggests that WBAX-SPI EFGs hold promising potential for industrial applications in the delivery of β-carotene.

Film-forming properties and mechanisms of soy protein: Insights from β-conglycinin and glycinin

Extensive research has been conducted on soy protein films; however, limited information is available regarding the influence of the major components, β-conglycinin (7S) and glycinin (11S), on the film-forming properties of soy protein. This study aimed to isolate the 7S and 11S fractions in order to prepare films and investigate the impact of varying 7S/11S ratios on the film-forming solutions (FFS) and film properties. The findings revealed that higher 11S ratios led to increased protein aggregation, consequently elevating the storage modulus (G') of the FFS. Notably, an optimal 7S/11S ratio of 7S1:11S2 (CF3) significantly enhanced the film's water resistance. Specifically, it enhanced the water contact angle by an impressive 17.44 % and reduced the water vapor transmission rate by 27.56 %. These improvements were attributed to intermolecular interactions, involving hydrogen bonds and salt bridges, between the amino acid residues of 7S and 11S. As a result, a more uniform and dense microstructure was achieved. Interestingly, the mechanical and optical properties of the film were maintained by the different protein fractions examined. In summary, this study contributes to the understanding of the film-forming properties of soy protein, particularly the role of 7S and 11S.

In vitro protein digestibility of different soy-based products: effects of microstructure, physico-chemical properties and protein aggregation

This study investigates the effects of protein structure and food microstructure on the in vitro protein gastrointestinal digestibility of different soy-based products, such as soy drink, reconstituted soy drink powder, firm tofu, and yuba. The results of the chemical cross-linking analysis showed that hydrogen bonds and hydrophobic interactions were the main forces driving protein aggregation in (reconstituted) soy drink powder and firm tofu, whereas disulphide bonds were significantly more important for soy drink and yuba. The β-sheet content of soy drink (36.5%) was lower than that of yuba (43.3%), but significantly higher than those of soy drink powder (23.2%) and firm tofu (29.8%). The in vitro protein digestibility decreased in the order of firm tofu > reconstituted soy drink powder > yuba > soy drink. Principal component analysis showed that protein gastrointestinal digestibility was positively correlated with the surface SH content and soluble protein content released by SDS + urea (SB-SA) but negatively correlated with the disulphide bonds and β-sheet content for the four soybean products.

Protein digestibility of textured wheat protein (TWP)-based meat analogs: (II) Effects of sodium tripolyphosphate

In this study, the effects of adding sodium tripolyphosphate during the extrusion of textured wheat protein (TWP)-based meat analogs were investigated. Five TWPs (TWP-C0, TWP-C0.10, TWP-C0.25, TWP-C0.50, and TWP-C0.75) were prepared with sodium tripolyphosphate concentrations of 0%, 0.10%, 0.25%, 0.50%, and 0.75%, respectively. The fibrous structure of TWPs was analyzed by determining their textural properties, degree of texturization, microstructure, and protein bonds. When the concentration of sodium tripolyphosphate increased from 0% to 0.75%, the fibers in TWPs became more regular and finer with smaller pores, the degree of texturization increased from 2.10 ± 0.09 to 2.73 ± 0.07, and the proportions of solubilized protein from the breaking of hydrophobic bonds and disulfide bonds increased from 2.06 ± 0.14% and 1.38 ± 0.11% to 3.42 ± 0.12% and 1.74 ± 0.05%, respectively. The results of particle size, soluble nitrogen content, and free amino acids of samples during digestion indicated that the disintegration rate and protein digestibility of TWPs increased with the increase in the concentration of sodium tripolyphosphate. After gastrointestinal digestion, the total free amino acids released in TWP-C0, TWP-C0.10, TWP-C0.25, TWP-C0.50, and TWP-C0.75 were 391.5 ± 2.2, 403.9 ± 1.5, 430.0 ± 3.6, 473.8 ± 2.9 and 485.3 ± 5.73 mg/10 g digesta, respectively. Sodium tripolyphosphate may improve the protein digestibility of TWPs by forming a finer fibrous structure with a more unfolded protein structure and more hydrophobic groups being exposed to enzymes.

Structural, functional properties of protein and characteristics of tofu from small-seeded soybeans grown in the Loess Plateau of China

The structural, functional properties of protein isolated from small-seeded soybeans were investigated and characteristics of tofu were studied. Small-seeded soybean protein had obvious α', α, β, acidic and basic subunits bands and two endothermic peaks (76.02-76.63℃ and 91.94-94.25℃). Small-seeded black soybean protein isolates (SBSPI) had more β-sheet (31.90-33.54%) structure, while small-seeded yellow soybean protein isolates (SYSPI) had more α-helix (18.89-20.72%) structure. SYSPI had higher fluorescence intensity (839.10-847.80) than SBSPI (482.70-565.10). SBSPI exhibited higher surface hydrophobicity (939.51-1252.75) and water absorption capacity (8.07-8.50 g/g). Tofu made from small-seeded yellow soybeans had higher yield (549.46-560.23 g/100 g soybean) and was brighter (L*, 74.61-77.48) and more yellowish (b*, 14.83-14.95) in color. Tofu made from Fugu small-seeded black soybean (FGSBS) had the highest hardness (178.52 g), adhesiveness (-25.77 g.sec), chewiness (87.45 g) and resilience (0.26), signifying a more compact structure.

Heating temperatures affect meat quality and vibrational spectroscopic properties of slow- and fast-growing chickens

This study determined the effect of water bath cooking (70°C and 90°C for 40 min) and the extreme heat treatment by an autoclave (121°C for 40 min) on the quality of breast meat of a fast-growing chicken, commercial broiler (CB), and slow-growing chickens, Korat chicken (KC), and Thai native chicken (NC) (Leung Hang Khao), by vibrational spectroscopic techniques, including synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy and Fourier transform Raman (FT-Raman) spectroscopy. Taste-enhancing compounds, including inosine-5'-monophosphate (IMP) and guanosine-5'-monophosphate (GMP), were better retained in cooked KC and NC meats than in cooked CB meat (P < 0.05). The high heat treatment at 121°C depleted the amount of insoluble collagen in all breeds (P < 0.05). Shear force values of slow-growing chicken meat were not affected by high heating temperatures (P > 0.05). In addition, the high heat treatment increased protein carbonyl (P < 0.05), while no effect on in vitro protein digestibility (P > 0.05). SR-FTIR microspectroscopy performed better in differentiating the meat quality of different chicken breeds, whereas FT-Raman spectroscopy clearly revealed differences in meat qualities induced by heating temperature. Based on principal component analysis (PCA), distinct characteristics of chicken meat cooked at 70°C were high water-holding capacity, lightness (L*), moisture content, and predominant α-helix structure, correlating with Raman spectra at 3,217 cm^-1 (O-H stretching of water) and 1,651 cm^-1 (amide I; α-helix). The high heating temperature at 90°C and 121°C exposed protein structure to a greater extent, as evidenced by an increase in β-sheets, which was well correlated with the Raman spectra at 2,968 and 2,893 cm^-1 (C-H stretching), tryptophan (880 cm^-1), tyrosine (858 cm^-1), and 1,042, 1,020, and 990 cm^-1 (C-C stretching; β-sheet). SR-FTIR and FT-Raman spectroscopy show potential for differentiation of chicken meat quality with respect to breeds and cooking temperatures. The marked differences in wavenumbers would be beneficial as markers for determining the quality of cooked meats from slow- and fast-growing chickens.

Effects of Packaging Materials on Structural and Simulated Digestive Characteristics of Walnut Protein during Accelerated Storage

Walnuts are rich in fat and proteins that become oxidized during the processing and storage conditions of their kernels. In this study, the effect of three packaging materials (e.g., polyethylene sealed packaging, polyamide/polyethylene vacuum packaging, and polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging) were investigated on the oxidation, structural and digestive properties of walnut kernel proteins. Results showed that the amino acid content gradually decreased and carbonyl derivatives and dityrosine were formed during storage. The protein molecule structure became disordered as the α-helix decreased and the random coil increased. The endogenous fluorescence intensity decreased and the maximum fluorescence value was blue-shifted. After 15 days of storage, surface hydrophobicity decreased, while SDS-PAGE and HPLC indicated the formation of large protein aggregates, leading to a reduction in solubility. By simulating gastrointestinal digestion, we found that oxidation adversely affected the digestive properties of walnut protein isolate and protein digestibility was best for polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging. The degree of protein oxidation in walnuts increased during storage, which showed that except for fat oxidation, the effect of protein oxidation on quality should be considered. The results of the study provided new ideas and methods for walnut quality control.

Physicochemical properties, texture, and in vitro protein digestibility in high-moisture extrudate with different oil/water ratio

Oil addition is challenging during high-moisture extrusion due to the negative fiber formation effects. A previous study found that oil-in-water (O/W) emulsions could significantly increase the oil content in high-moisture extrudates, but the molecular mechanism remained unclear. This study aimed to determine O/W emulsion influence on protein physicochemical properties in SPI extrudates during high-moisture extrusion. O/W emulsions were mixed with soy protein isolates (SPI) to prepare extrudates with oil/water ratios of 0/65, 4/61, and 8/57 (w/w). SDS-PAGE and ATR-FTIR analysis showed that higher oil/water ratios enhanced protein aggregation and promoted alteration from β-sheet to random coil in SPI extrudates, which could be correlated to the reduction of protein solubility. The color was altered to lighter and yellow, and hardness, chewiness, and fiber degree decreased with increased oil/water ratios in SPI extrudates. In addition, in vitro digestion analyses showed that higher oil content contributed to improved protein digestibility.

Separation and purification of antioxidant peptides from purple speckled kidney bean by macroporous adsorption resin and analysis of amino acid composition

The protein hydrolysate of purple speckled kidney bean (PSKB) was used as the raw material in this study, and the antioxidant peptide of the PSKB protein hydrolysate was purified using macroporous resin. The XAD-7HP macroporous resin was selected as the best purification material, and the static adsorption-desorption of the purified PSKB antioxidant peptide was optimized. The optimum static adsorption and desorption conditions were as follows: the adsorption capacity reached 11.93 ± 0.11 mg/ml at pH 7 for 24 h, and the desorption capacity was 5.24 ± 0.04 mg/ml with 60% ethanol for 30 min. Under this condition, the amount of antioxidant peptide obtained by adsorption-desorption was the highest. The optimum process conditions were as follows: the appropriate flow rate was 1 ml/min, and the optimal injection volume was 40 ml. The adsorption amount at this time can reach 12.19 ± 0.15 mg/ml. The components with an elution time of 10-30 min were separated using the reversed-phase high-performance liquid chromatography (RP-HPLC) technique to obtain three main components, namely, RP₁, RP₂, and RP₃. The DPPH free radical scavenging ability reached 56.26 ± 0.56, 66.42 ± 0.56, and 78.57 ± 0.56%, respectively, which were 36.65, 46.34 ± 0.56, and 54.39 ± 0.56% higher than those before purification. The amino acid sequences of the three components were identified as Phe-Leu-Val-Asp-Arg-Ile, Phe-Leu-Val-Ala-Pro-Asp-Asp, and Lys-Asp-Arg-Val-Ile-Ser-Glu-Leu.