Influence of heat treatment before and/or after high-pressure homogenization on the structure and emulsification properties of soybean protein isolate

Effect of hot-air drying on the structure, physicochemical properties, and digestibility of corn germ protein from two cultivars cultivated in East China

In recent times, the use of corn germ protein (CGP) has become more widespread. However, hot-air drying does not consider its effect and variability on the CGP properties. This study involved drying two types of corn grains from two different cultivars (Denghai-685 and Xianyu-335) cultivated in East China. The corn grains with different initial moisture content (20, 25, and 30%) were dried using hot-air at various temperatures (60, 90, and 120 °C). The CGP was separated and analyzed its properties and digestibility. Compared to naturally dried samples, hot-air dried CGPs exhibited poor emulsifying and foaming properties. The average particle size, sulfhydryl group content, and surface hydrophobicity increased with the rise in drying temperature. As well as the changes in the secondary, tertiary structures and gastric and intestinal digestibility of CGPs. The results showed that while both cultivars responded similarly to varying drying conditions, there were observable differences in the degree of change in surface hydrophobicity, emulsifying stability, and digestibility. These findings suggest cultivar-based variations in CGP properties that may influence their food processing applications.

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Soy protein-gellan gum noncovalent complexes stabilized emulsion: Effect of heating and pH on emulsion stability

This paper investigated the effects of heating and pH on the stability of emulsions of non-covalent complexes of gellan gum (GG) and soy protein isolate (SPI). As a result, the GG-SPI complexes stabilized emulsion exhibited a minimum emulsion particle size (945 ± 23 nm), a maximum absolute values of zeta-potential (-32.7 ± 0.81 mV), the highest values of emulsion activity index (EAI) and stability index (ESI) (132 ± 4.7 min) when emulsion was prepared under the following conditions: oil phase ratio of 18 %, polysaccharide-protein proportion of 1:8 (w/w), homogeneous pressure at 80 MPa and homogeneous time at 4 min. GG-SPI emulsion had the best emulsification performance at pH 9.0 and 75 °C owing to the protein defolding occurred, the content of α-Helix increased, hydrophobic groups were exposed, and the number of negative groups on the surface of proteins increased under the high pH and high temperature conditions. The experimental results revealed the key role of heating and pH treatment for protein emulsion stability regulation, which will enrich the application of gellan gum in soy protein emulsions and provide an important theoretical basis for the future application of emulsion modification.

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.

Investigation of Emulsifying Properties and Stability of Fish Gelatin and Tea Saponin Complex Emulsion System

In this study, environmental stability, rheological properties, and structural characterization of co-stabilized emulsions using fish gelatin (FG) and tea saponin (TS) were investigated. The results demonstrated that the addition of TS significantly enhanced the emulsifying properties of FG, and the FG-TS0.1% emulsion had the smallest particle size. TS and FG co-stabilized emulsions provided resistance to salt and high temperatures. Optical microscopy and CLSM showed that the addition of TS made FG more effectively adsorb at the oil-water interface, leading to the formation of more uniform oil droplet sizes. Additionally, the addition of TS increased the viscosity of FG emulsions, which reduced emulsion flocculation. Results of intrinsic fluorescence, FTIR, and surface hydrophobicity revealed that the addition of TS altered the secondary structure of FG, enhancing surface hydrophobicity and improving emulsification. In conclusion, the moderate addition of TS significantly enhanced the emulsification and rheological properties of FG, suggesting new potential applications for FG in various industries.

pH-induced interface protein structure changes to adjust the stability of tilapia protein isolate emulsion prepared by high-pressure homogenization

The pH is a crucial external factor affecting the structure and emulsification characteristics of proteins. The current study aimed to reveal the correlation between the secondary structure changes and tilapia protein isolate (TPI) emulsion stability under different pH (3.0-10.0) prepared by high-pressure homogenization. The results showed that TPI with significantly increased solubility and emulsifying properties when the pH keep away from the isoelectric point (pH 5.0). Meanwhile, TPI emulsions presented significantly enhanced stability (with decreased particle size, increased zeta potential, creaming index close to 0, and uniform dispersion of droplets) at pH 3.0 and 10.0. Interface-adsorbed protein mainly consists of a myosin-heavy chain and actin, and the secondary structure was significantly influenced by pH and high-pressure homogenization. The α-helix will be transformed into β-sheet and β-turn when pH is closer to pH 5.0. However, the high-pressure homogenization induced α-helix conversion to β-sheet. The correlation analysis revealed that emulsion stability is positively correlated with α-helix and negatively correlated with β-sheet. This work provides a deep insight into the correlation between secondary structure changes and the stability of TPI emulsion as affected by pH to offer an alternative way to enhance TPI emulsion stability.

Ca2+-promoted free radical grafting of whey protein to EGCG: As a novel nanocarrier for the encapsulation of apigenin

Whey protein (WP) is often used as a delivery carrier due to its superior biological activity and nutritional value. Covalent binding of WP to epigallocatechin gallate (EGCG) can significantly improve the performance of WP in encapsulated materials. Nevertheless, the preparation of WP-EGCG covalent complexes still suffers from low grafting rates. Studies have shown that calcium ions (Ca2+) can modify the structure of proteins. We therefore explored the effect of calcium chloride (CaCl2) on the free radical grafting of EGCG and WP. The experimental results showed that the grafting rate of free radicals increased by 17.89% after adding Ca2+. Furthermore, the impact of WP-EGCG-Ca2+ covalent complex on the entrapment efficiency of apigenin (AP) was further examined, and the results revealed that the entrapment rate could reach 93.66% at an apigenin concentration of 0.2 mg/mL. Simulated gastrointestinal digestion showed that WP-EGCG-Ca2+ covalent complex could significantly improve the bioavailability of AP. The study provides new ideas to broaden the application of WP as a carrier for delivering bioactive substances.

Enhancing the Stability of Litsea Cubeba Essential Oil Emulsions Through Glycosylation of Fish Skin Gelatin via Dry Maillard Reaction

Emulsions are widely utilized in food systems but often face stability challenges due to environmental stresses, such as pH, ionic strength, and temperature fluctuations. Fish skin gelatin (FSG), a promising natural emulsifier, suffers from limited functional properties, restricting its broader application. This study explored the enhancement of emulsion stability in Litsea cubeba essential oil systems through the glycosylation of fish skin gelatin (FSG) with dextran via the dry Maillard reaction. Among dextrans of varying molecular weights (10 kDa, 100 kDa, 200 kDa, and 500 kDa), the 200 kDa dextran exhibited the best emulsification performance, achieving a remarkable 160.49% increase in stability index. The degree of grafting (DG) increased with molecular weight, peaking at 34.77% for the 500 kDa dextran, followed by 23.70% for the 200 kDa variant. The particle size of the FSG-Dex 200 kDa conjugate emulsion was reduced to 639.1 nm, compared to 1009-1146 nm for the unmodified FSG, while hydrophobicity improved by 100.56%. The zeta potential values approached 30 mV, indicating enhanced stability. Furthermore, glycosylation significantly improved antioxidant activity, as evidenced by increased radical scavenging capacity in both DPPH and ABTS assays. These findings underscore the potential of glycosylated FSG as a natural emulsifier in food applications.

Starch hydration properties in relation to kinetic modelling of mass transfer and properties of deep-frying batter

The hydration properties of starch were examined in relation to mass transfer and the characteristics of deep-frying batter. With extended deep-frying, the oil content in all samples increased, while the moisture content exhibited an inverse trend. Analyses of zeta potential, disulfide bonds, secondary structure, particle size of the proteins, thermal properties, and water status indicated that prolonged deep-frying time facilitated protein aggregation and led to a decrease in both gelatinization enthalpy (ΔH) and the percentage of bound water. Additionally, deep-frying batter containing starch with medium hydration properties (carboxymethyl freeze-thawed tapioca starch), accelerated protein aggregation, delayed the dissipation of bound water, and significantly reduced both gelatinization and ΔH. This ultimately weakened the intensity of mass transfer, thereby diminishing oil distribution. The Pearson's correlation test confirmed a negative correlation between mass transfer intensity and starch hydration properties, indicating that both parameters significantly influenced the characteristics of the deep-frying batter.

High-pressure homogenization to improve the stability of liquid diabetes formula food for special medical purposes: Structural characteristics of casein-polysaccharide complexes

The stability of diabetes formula food for special medical purposes (D-FSMP) was improved by high-pressure homogenization (HPH) at different homogenization pressures (up to 70 MPa) and number of passes (up to 6 times). The process at 60 MPa/4 times was the best. Casein had the highest surface hydrophobicity in this condition. The casein-polysaccharide complexes were endowed with the smallest size (transmission electron microscopy images). The complex particles exhibited nearly neutral wettability (the three-phase contact angle was 90.89°), lower interfacial tension, and the highest emulsifying activity index (EAI) and emulsifying stability index (ESI). The prepared D-FSMP system exhibited the narrowest particle size distribution range, the strongest interfacial deformation resistance and the best storage stability. Therefore, an appropriate intensity of HPH could enhance the stability of D-FSMP by improving the interfacial and emulsifying properties of casein-polysaccharide complexes. This study provides practical guidance on the productions of stable D-FSMP.

Impact of pilot-scale microfluidization on soybean protein structure in powder and solution

The effect of microfluidization treatment on the primary, secondary, and tertiary structure of soybean protein isolate (SPI) was investigated. The samples were treated with and without controlling the temperature and circulated in the system 1, 3, and 5 times at high pressure (137 MPa). Then, the treated samples were freeze-dried and reconstituted in water to check the impact of the microfluidization on two different states: powder and solution. Regarding the primary structure, the SDS-PAGE analysis under reducing conditions showed that the protein bands remained unchanged when exposed to microfluidization treatment. When the temperature was controlled for the samples in their powder state, a significant decrease in the quantities of β-sheet and random coil and a slight reduction in α-helix content was noticed. The observed decrease in β-sheet and the increase in β-turns in treated samples indicated that microfluidization may lead to protein unfolding, opening the hydrophobic regions. Additionally, a lower amount of α-helix suggests a higher protein flexibility. After reconstitution in water, a significant difference was observed only in α-helix, β-sheet and β-turn. Related to the tertiary structure, microfluidization increases the surface hydrophobicity. Among all the conditions tested, the samples where the temperature is controlled seem the most suitable.

Pressure-dominated steam explosion for modifying textured soy proteins: Structure and in vitro digestion kinetics

Textured Soy Proteins (TSPs) have been employed as building blocks in various food processes, but their availability remains limited. In this research, influence of Steam Explosion (SE) with pressure ranges (0, 0.5, 1.0, 1.5 MPa) on the structure and in vitro digestibility of TSPs was investigated. The results showed that 0.5 and 1.0 MPa significantly increased the relative content of β-sheets and decreased the relative content of α-helices and β-turns. Correlation analysis revealed that the structural changes made the TSP brittle, with lower thermal stability and resistance to digestion. Moreover, SE decreased the degree of hydrolysis of TSPs in the gastric stage, with the lowest degree observed for the TSP at 0.5 MPa. However, in the intestinal phase, 1.0 and 1.5 MPa significantly increased the hydrolysis degree. These findings provide a better understanding of the SE pressure-modulated quality characteristics of TSPs and suggest the processing potential of modified TSPs as functional ingredients.