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To identify the effects of charged states on the formation and disaggregation of soy protein isolate (SPI) fibril, we studied the thermal aggregation behaviors of the constituent peptides of SPI fibril (CPSF) at various pH values (2–10) and investigated the structural changes of SPI fibril with increasing pH (2–11). Results showed that CPSF would assemble into diverse shapes at different pH values, among which the aggregates contained multiple β-sheet structures at pH less than 6, but these β-sheets were stacked to form fibrils only at pH 2. The damages from the increased pH to SPI fibril structure could be roughly divided into two stages, as follows: when pH was less than or equal to 6, the morphology of fibrils changed markedly due to electrostatic neutralization; at pH larger than 6, the fibrils suffered great losses in β-sheet, causing its structure to disintegrate rapidly. This study could provide theoretical reference to improve the pH stability of SPI fibril from the aspects of preparation and structural protection of the fibril.

Protein hydrolysates from various sources, including tuna cooking juice, soy protein isolate, sodium caseinate, wheat gluten and skin gelatin from porcine, tilapia, halibut and milkfish were analyzed to screen their antiproliferative activities against the human oral squamous carcinoma cell line, HSC-3. The soy protein isolate was selected for further investigations based on its hydrolysates with bromelain (SB) and thermolysin (ST), showing the greatest inhibition of cell growth. The SB and ST hydrolysates showed antiproliferative activities up to 35.45–76.39% against HSC-3 cells at 72 h, and their IC50 values were 0.74 and 0.60 mg/mL, respectively. SB and ST induced cell cycle arrest in the S phase through a pathway independent of p21 and p27 protein expression. Further, ST induced the apoptosis of HSC-3 cells by downregulating expression of Bcl-2, PARP, caspase 3 and caspase 9, but an upregulating expression of p53 and cleaved caspase 3. Unlike ST, SB may induce necrosis on HSC-3 cells. Thus, soybean hydrolysates may be a good source for providing antiproliferative peptides against HSC-3, while SB and ST may have the potential to be developed as functional foods.

A carboxypeptidase M32 (CPM32) gene (cpm32) from Bacillus megaterium was cloned. CPM32 exhibited the highest sequence similarity of 79.3% with the same from Priestia veravalensis. CPM32 was fused with the signal peptides AmyQ (SPamyQ), AprE (SPaprE), NprB (SPnprB) in Bacillus subtilis WB600, and the highest CPM32 activity of 5320 U/mL was achieved when it was fused with SPamyQ. The purified enzyme (CPM32), 58.6 kDa, was most active at pH 8.0 and 60 °C, respectively, and it was stable over a broad pH range of 5.0–9.0 and an extensive temperature of 30–60 °C. Co2+ and Zn2+ could activate the enzyme activity by 600% and 334%, respectively. CPM32 could cleave most amino acid residues except Pro from chain's C-terminus. N-benzyloxycarbonyl-l-phenylalanyl-l-tyrosine (Z-Phe-Tyr) was the optimal substrate, for which CPM32 exhibited Km 0.6 mmol/L and kcat/Km 82.2 L/mmol s. Debittering soybean isolates using CPM32 (supplemented with 4% alkaline protease, w/w) resulted in a reduction in bitterness value of 47.6% to a commercially acceptable level. Applied to the hydrolysis of soy isolate protein, the bitterness of the hydrolyzates is significantly reduced and the flavor of the soy protein isolate hydrolysates is effectively improved.

The stability and digestive properties of a dual-protein emulsion consisting of soy protein isolate (SPI) and whey protein isolate (WPI) have been systematically studied. The results showed that the particle size and viscosity of the dual-protein emulsion system decreased continuously with the increase in WPI, and this might be related to the large amount of electric charge on the surface of the emulsion droplets. Dual-protein emulsions with ratios of 3:7 and 5:5 showed the highest emulsion activity, while emulsion stability increased with the increase in WPI. The thicker adsorption layer formed at the interface might have contributed to this phenomenon. After in-vitro-simulated digestion, the emulsion droplet particle size increased substantially due to the weakened electrostatic repulsion on the droplet surface, especially for the intestinal digestion phase. Meanwhile, WPI accelerated the release of free fatty acids in the digestion process, which played a positive role in the nutritional value of the dual-protein emulsion. In accelerated oxidation experiments, WPI also improved the antioxidant properties of the dual-protein emulsion system. This study will provide a new insight and necessary theoretical basis for the preparation of dual-protein emulsions.

The potential of soy protein isolate (SPI) and maltodextrin (MD) conjugates for the development of plant-based chiffon cakes with desirable properties was investigated by optimizing the SPI-MD conjugation process through wet heat treatment. The SPI:MD ratio was fixed at 2:1, and the heating time was varied (0, 60, and 180 min). Key functional properties (degree of grafting, zeta potential, protein solubility, and foaming properties) were analyzed. Heating for 60 min with a 2:1 SPI:MD ratio (C60) provided the most favorable outcomes, including higher protein solubility, optimal zeta potential, and improved foaming capacity, leading to better cake texture and stability. The C60 sample is a potentially viable egg substitute for plant-based chiffon cakes, offering a promising approach for developing vegetarian bakery products of similar quality as their animal-based counterparts. Further research is required to refine this conjugation method and explore its broader applications in plant-based food development.

There is an increasing interest in the development of cholesterol-free mayonnaise through the strategy to use food-grade polymeric emulsifiers to substitute or partially substitute egg yolk. In addition, mayonnaise-type emulsions or mayonnaise are usually susceptible to freezing. The work reported that a heated soy protein isolate (SPI) could perform as an effective sole stabilizer for mayonnaise-type high internal phase emulsions (HIPEs) with an outstanding freeze-thaw stability. Such HIPEs with a self-supporting morphology could be stabilized using the heated SPI at a protein concentration (c) as low as 0.3 wt.%. Increasing the c from 0.3 to 4.0 wt.% resulted in a progressive strengthening of gel network for the mayonnaise-type HIPEs, and the formation of finer droplets. All the as-formed HIPEs exhibited an elasticity-dominated rheological behavior, with the stiffness increasing the c. The elasticity of the gel-like HIPEs at low c values (e.g., 0.3 wt.%) was mainly associated with the formation of bridged emulsions, while that at high c values was more associated with the inter-droplet hydrophobic interactions between protein-coated droplets. All the mayonnaise-type HIPEs, formed even at a c value of 0.3 wt.%, were extremely stable against the freeze-thaw treatment. The high freeze-thaw stability seemed to be unrelated to the formation of ice crystals during the freezing. All the freeze-thawed HIPEs still exhibited a high long-term storage stability against coalescence, and their elasticity on the contrary became strengthened after the long-term storage. The findings have great implications for the development of cholesterol-free mayonnaise with a high freeze-thaw stability, suitable for food formulations.

The effects of cellulose nanocrystals (CNC) and microcrystalline cellulose (MCC) on the gel properties and microstructure of glucono-δ-lactone-induced soy protein isolate (SPI) gels were investigated. The water-holding capacity, gel strength, and viscoelastic modulus of CNC–SPI gels were positively associated with CNC concentration from 0 to 0.75% (w/v). In contrast, MCC–SPI gels exhibited decreased water-holding capacity, gel strength, and viscoelastic modulus. All composite gels displayed high frequency dependence and the typical type I (strain thinning) network behavior. Changes in viscoelasticity under large strain were correlated with differences in the microstructure of SPI composite gels. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) showed that CNC were more evenly and steadily distributed in the protein matrix and formed a compact network structure. In contrast, MCC–SPI gels exhibited a discontinued and rough gel network with some large aggregates and pores, in which MCC was randomly entrapped. Fourier transform infrared spectroscopy (FTIR) and molecular forces results revealed that no new chemical bonds were formed in the gelation process and that the disulfide bond was of crucial importance in the gel system. With the addition of CNC, electrostatic interactions, hydrophobic interactions, and hydrogen bonds in the SPI gel network were significantly strengthened. However, the incorporation of MCC might obstruct the connection of the protein network. It is concluded that both cellulose type and concentration affect gelling properties.

The effect of electrolysis on soy protein isolate (SPI) was studied by Raman spectroscopy and ultraviolet spectroscopy. The results showed that with the prolongation of electrolysis time, the α-helix content decreased first and then increased. Trp and Tyr residues tended to be exposed from their original embedded state, while electrolysis gradually shifted the SPI disulfide bond from the g–g–g configuration to g–g–t and t–g–t configuration. Therefore, the electrolysis treatment influences the SPI disulfide bond, resulting in intermolecular disulfide bond. Raman spectra showed the secondary and tertiary structure changes of SP and revealed that the structure of SPI would be affected by electrolysis. And the results of UV scanning spectrum confirm the above conclusions.

With the increasing awareness of environmental protection, the interest in the development of biodegradable materials has become increasingly popular. At present, wheat gluten protein (WGP), soybean protein isolate (SPI), and Zein have made some progress in the application of packaging materials. At the same time, beeswax (BW) is widely applied in the preparation of food coatings. In this study, composite films were prepared by adding BW to three different types of proteins. Various properties of the composite film, such as thickness, color, mechanical properties, and thermal stability, were tested. The thickness of the film was significantly increased after adding BW. Regarding the mechanical properties, the BW didn’t improve the composite film’s tensile strength. The results of the SEM indicated that the surface morphology of the composite films changed due to the interaction between BW and protein molecules. Besides, the addition of BW resulted in a decrease of thermal stability. The Td of the Zein film (77 ℃) and WGP film (106 ℃) were decreased to 72℃ and 98℃, respectively. The study shows that the composite films will have the opportunity to be applied in the food package field in the future and further replace the traditional petroleum-based films.

This study aimed to investigate the effect of hydrolyzed soy protein isolate (HSPI) as a plasticizer in the soy protein mixture-wheat gluten (SP-WG) extrudates on its structural and mechanical properties during high moisture extrusion. Those SP were prepared by mixing soy protein isolate (SPI) and HSPI with different ratios. HSPI primarily consisted of small molecular weight peptides measured with size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The elastic modulus of SP-WG blends decreased with increased HSPI contents through the closed cavity rheometer. Adding HSPI at low concentrations (≤30 wt% of SP) enhanced a fibrous appearance and higher mechanical anisotropy while adding more HSPI resulted in a compact and brittle structure and tended to be isotropic. It can be concluded that the partial addition of HSPI as a plasticizer can promote the formation of a fibrous structure with enhanced mechanical anisotropy.