Stability improvement of emulsions stabilized by covalent conjugation with glycosylated black bean protein and EGCG (BBPI-G–EGCG) was studied through structure changes of proteins and emulsion properties.

In this experiment, the peanut protein isolate (PPI), soybean protein isolate (SPI), rice bran protein isolate (RBPI), and whey protein isolate (WPI) were modified by linking chlorogenic acid covalently and linking dextran by Maillard reaction to prepare protein-chlorogenic acid-dextran (PCD) conjugates. As for structures, conformational changes of conjugates were determined by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE), Fourier transform infrared (FT-IR), and fluorescence measurements. The molecular weights of PCD conjugates became larger, the structure became disorder, and the amino acid residues inside the protein were exposed to the polar environment when compared to protein-chlorogenic acid (PC) and native proteins (NPs). As for properties, the interfacial tension reduced and antioxidant activity of PCD conjugates enhanced in varying degrees. Based on this, PCD conjugates were used as emulsifiers in order to investigate the properties of nanoemulsions and compared with PC conjugates and NPs. The mean droplet diameters (MDD) results showed that the nanoemulsions that were stabilized by PCD conjugates had the smallest particle sizes and exhibited uniformly dispersed spherical shapes. The storage and oxidative stabilities of PCD conjugates were also significantly improved. In comparison, nanoemulsion that was stabilized by PPI-chlorogenic acid-dextran conjugate had the smallest particle size and optimal stability among four protein stabilized nanoemulsions.

Heat-induced composite gel systems consisting of different soybean protein isolate (SPI) and potato protein (PP) mixtures were studied to elucidate their “backbone” and property changes. This was achieved by comparing the ratio of non-network proteins, protein subunit composition, and aggregation of different gel samples. It was revealed that SPI was the “gel network backbone” and PP played the role of “filler” in the SPI-PP composite gel system. Compared with the composite gels at the same ratio, springiness and WHC decrease with PP addition. For hardness, PP addition showed a less linear trend. At the SPI-PP = 2/1 composite gel, hardness was more than doubled, while springiness and WHC did not decrease too much and increased the inter-protein binding. The hydrophobic interactions and electrostatic interactions and hydrogen bonding of the SPI gel system were enhanced. The scanning electron microscopy results showed that the SPI-based gel system was able to form a more compact and compatible gel network. This study demonstrates the use of PP as a potential filler that can effectively improve the gelling properties of SPI, thus providing a theoretical basis for the study of functional plant protein foods.

At present, the changes in fibrous structure of plant proteins improved by polysaccharides during high-moisture extrusion cooking (HMEC) are still unclear. In this study, different additions (1, 2, 3, 4, and 5%) of sodium alginate (SA), xanthan gum (XG), and maltodextrin (MD) were used in the preparation of organised protein products based on soybean protein and wheat protein under high moisture extrusion conditions. It was revealed that SA-4%, XG-2%, and MD-2% (w/w) significantly enhanced the structural and physical properties of the fibres. The polysaccharides increased the water distribution of extrudates by enhancing protein-water interactions through hydrogen bonding, with MD-2% having the strongest ability to trap free water. The mechanism by which the polysaccharides improved the fibrous structure of extrudates involved the reorganization of molten proteins from the die head region to the cooling region, formation of new molecular bonds and enhancement of thermal stability. XG-2% significantly increased the β-sheet structure in the molten region (48.9 ± 1.35%) and showed the best thermal stability. Overall, SA-4% was able to better maintain the molecular bonding transformation and strong water absorption, which stabilised the protein conformation and formed the highest fibrous degree (2.1 ± 0.03). This suggests that the properties of the three polysaccharides can be used as modifiers of high water extruded plant proteins to improve the extruded materiality, functional and nutritional properties.