Functionalization of pine kernel protein by pH-shifting combined with ultrasound treatments: Further improvement with increasing acidity

Comparative efficacy of natural seed coats in regulating protein aggregation in pre-roasted pine kernels and enhancing associated techno-functionality

To investigate the regulatory effect of pine nut seed coats on protein techno-functionality during pre-roasting, proteins from kernels subjected to various treatments, including de-shelling, de-skinning, and roasting with or without seed coat, were compared in terms of gelation behavior and interfacial properties. Results indicated that roasting without the seed coat caused disordered unfolding of proteins and the formation of heterogeneous, blocky protein aggregates. In contrast, skin-coating facilitated polyphenol binding with proteins by 2.5-fold, promoting ordered aggregation. Solubility, emulsification activity, emulsion stability, and foaming capacity increased by 34.52 %, 210.46 %, 59.51 %, and 55.54 %, respectively, while the gel network formed uniformly. Shell-coating promoted the formation of heat-stable aggregates, characterized by strong hydrogen bonds, disulfide bonds, and α-helical conformation. The seed coat was found to mediate roasting-induced modifications in protein spatial conformations and aggregate morphological transformations. This study proposes a novel strategy for modulating the functionality of nut proteins.

pH shifting treatment of egg yolk granules /salted ovalbumin mixed gels: Reassembled of egg yolk granules effects on heat-induced amorphous aggregates

In this study, we propose three methods of acidic pH shifting of egg yolk granules (EYGs) to investigate effects of EYGs structure on properties of EYGs-salted ovalbumin (SO) gels. Different pH parameters affect protein unfolding behavior, as well as assembly of high-density lipoprotein (HDL) and phosvitin during acidification. The main mechanism was a change in the microenvironment of hydrophobic amino acid residues and new hydrogen bonds, which induced the reassembly. Besides, low-content EYGs increased the mixed gel network structure density, cohesiveness (0.12-0.14) and chewiness (29.46-49.11). While mixed gels with high content EYGs had higher hardness and recovery rate, and were more tightly bound to water molecules. EYGs-4-6 exhibited greater hydrogen bonding forces, which could lead to a more rigid network and greater potential for use as an active filler. Our study tracked the trajectory of pH-shifting preparations of reassembled EYGs while providing new insight into nutritional value of SO gel.

Synergistic Effects of Ultrasound and pH-Shifting on the Solubility and Emulsification Properties of Peanut Protein

Peanut protein is a byproduct of peanut oil extraction with limited applications within the food sector due to its low solubility and emulsifying properties. This study investigated the influences and mechanisms of high-intensity ultrasound (HIU, 200~600 W) and pH-shifting (pH 12), either individually or jointly, on the structure, solubility, and emulsifying properties of PP. Results indicated that the solubility of PP significantly increased after the combined treatment, particularly when the HIU power was 300 W (p < 0.05). Accordingly, emulsions prepared from it exhibited highest storage stability. Structural analysis indicated that the increased PP solubility (9.95% to 54.37%, p < 0.05) is mainly attributed to the structural changes that occur during protein unfolding, resulting in the uncovering of hydrophobic groups (7181.43 to 14,083.00, p < 0.05) and the reduction of α-helices (24.43% to 18.17%, p < 0.05). Moreover, confocal laser scanning microscopy of the emulsions revealed that the combination-treated PP resulted in smaller protein particle sizes (50.09 μm to 15.68 μm, p < 0.05), tighter adsorption on the oil-water interface, and a denser and more stable interfacial film compared to the native and the individual treatment, thereby enhancing the stability of the system. A rheological analysis confirmed that the combined treatment improved the interfacial properties of the protein, which was advantageous for emulsion stability. In conclusion, HIU combined with pH12-shifting can appreciably improve the solubility and emulsifying properties of PP to broaden its application prospects.

Dual modification of the aggregation behavior and in vitro digestion of oxidized pine kernel protein via a combination of homogenization and succinylation

Protein oxidation affects the high-value utilization of nuts as oxidative attack causes protein aggregation, thereby challenging their technological functionality. Herein, a strategy using homogenization-assisted octenyl succinic anhydride (OSA) modification was proposed to tailor the structure, aggregation behavior, and digestive characteristics of oxidized pine kernel proteins. Results indicated that the ratio of α-helices to β-turns ranged from as low as 0.43 up to 0.67 after homogenization, suggesting greater molecular flexibility. With increasing protein oxidation, the acylation degree exhibited an inverted V-shaped trend, peaking at 67.22 %. OSA treatment reduced the aggregation rate and prolonged the lag time of proteins by stabilizing the α-helices and β-turns, increasing hydrogen bonding, and decreasing hydrophobicity. This increased the solubility of oxidized pine kernel proteins by ~30 % and improved their fluidity and thermal stability. A lower degree of succinylation was associated with higher free sulfhydryl content and surface hydrophobicity, which facilitated the thermal aggregation and the formation of elastomeric gels. Furthermore, the in vitro dynamic digestion and morphological observations of hydrolysis products indicated that cotreated proteins exhibited higher digestibility and formed small spherical particles ranging from 405.50 to 676.50 nm. These findings provide a promising approach to mitigate the adverse effects of oxidation on nut proteins.

Structural changes and functional characteristics of common vetch isolate proteins altered by different pH-shifting treatments

To investigate protein structure and functional changes, common vetch protein isolate (CVPI) during pH-shifting were performed. Results showed secondary and tertiary structures of CVPI were improved during these treatments compared with the pH 7.0. Scanning electron microscopy showed the microstructure was changed from lamellar to spherical granular and rod-like structure during pH - shifting. Under 8 pH treatments (pH 2.0, 3.0, 12.0, 2.0 → 7.0, 3.0 → 7.0, 12.0 → 7.0, 11.0 → 9.0 and 11.0 → 7.0), the average particle sizes were smaller and from 82 to 146 nm. Under 8 pH treatments (pH 2.0, 3.0, 11.0, 12.0, 11.0 → 9.0, 11.0 → 7.0,12.0 → 9.0 and 12.0 → 7.0), the protein solubility was higher and from 63 to 86 %. Under 3 pH treatments (pH 2.0, 11.0 and 12.0), the emulsion activity index and emulsion stability index was higher and from 40 to 60 m2/g and from 54 to 97 min. Under 5 pH treatments (pH 2.0, 12.0, 11.0 → 9.0, 12.0 → 9.0 and 12.0 → 7.0), the foaming capacity and foaming stability was higher and from 145 to 185 % and from 67 to 82 %. Therefore, the pH - shifting treatment gave the CVPI improved characteristics in structural and functional properties.

pH-shifting treatment improved the emulsifying ability of gelatin under low-energy emulsification

The effects of pH-shifting treatments (pH 3, 5, 7, 9, and 11) on the stability of gelatin emulsions made by low-energy stirring were investigated. pH-shifting treatments significantly enhanced the ESI and EAI of the emulsion (P < 0.05) and reduced its particle size (P < 0.05) under low-energy emulsifying conditions. The pH11-7 shifting treatment significantly increased the degree of depolymerization and the level of ordered structure of gelatin (P < 0.05). These transformations resulted in a significant increase in the exposure of hydrophobic and negatively charged residues (P < 0.05) on the surface of gelatin, facilitating a faster adsorption rate of gelatin onto the oil-water interface as well as an increase in the amount of gelatin adsorbed at the interface. Moreover, the alkali-shifting treatment promoted the formation of a thin viscoelastic interfacial film, which contributed to the enhanced stability of the emulsion.

Effect of pH-shifting on the water holding capacity and gelation properties of mung bean protein isolate

In this study, alkaline pH-shifting modified the globular structure of mung bean protein isolate (MBPI) to form flexible and stretched structures. In contrast, acidic pH-shifting increased the rigidity of MBPI. The increased flexibility (at the level of the secondary structure) and newly exposed intermolecular amino acid groups induced by alkaline pH-shifting improved the water holding capacity and gelation properties of proteins. Specifically, MBPI treated at pH 12 (MP12) showed the most flexible structure and highest water holding capacity and gel formation properties (least gelation concentration). The water-holding capacity of native MBPI increased from 1.56 g/g to 4.81 g/g, and its least gelation concentration decreased from 22 % to 15 % by pH-shifting at pH 12. Furthermore, MP12 formed stronger and more elastic heat-induced gels than native MBPI. We identified significant differences in the structural properties and water holding capacity, and gelation properties of acidic and alkaline pH-shifted MBPI and investigated the gelation properties of MP12 including rheological and morphological analyses. Our findings can facilitate the use of mung beans as a protein source in a wide range of food applications, including plant-based and processed meats.