The interaction and antioxidant capacity between epigallocatechin gallate (EGCG) and β-lactoglobulin (β-Lg) under thermal treatments at 25–121 °C were investigated in this study. Fluorescence spectroscopy analysis showed that EGCG complexed with β-Lg mainly via non-covalent interactions and the binding affinity of EGCG to β-Lg was enhanced with heat treatment. EGCG showed a strong binding affinity to β-Lg after 85 °C heat treatment was applied, with a K_a of 30.69 (±0.87) × 10⁵ M⁻¹ (pH 6.8, 298 K). Circular dichroism (CD) results showed that heat treatment did not result in greatly affected changes in the β-Lg secondary structure induced by β-Lg–EGCG interactions. MALDI-TOF/TOF-MS analysis showed that β-Lg–EGCG covalent conjugates initially formed after heat was applied at 60 °C, and their proportions increased under heat treatment ranging from 85 to 121 °C. The amino group of a lysine residue was further confirmed as the covalent binding site of EGCG to β-Lg. The β-Lg–EGCG interaction showed little effect on the antioxidant capacity (ABTS and ferric reducing antioxidant power (FRAP) values) of EGCG after heat treatment at 25–60 °C, but did induce an obvious reduction at temperatures above 85 °C. This study will provide the foundation for the use of EGCG in processing dairy products (such as milk tea beverages) with desirable nutrition and physiological functions.

The interaction of soy protein isolate (SPI) and its hydrolysates (SPIHs) with cyanidin-3-O-glucoside (C3G) at pH 7.0 were investigated to clarify the changes in the antioxidant capacity of their complexes. The results of intrinsic fluorescence revealed that C3G binds to SPI/SPIHs mainly through hydrophobic interaction, and the binding affinity of SPI was stronger than that of SPIHs. Circular dichroism and Fourier-transform infrared spectroscopy analyses revealed that the interaction with C3G did not significantly change the secondary structures of SPI/SPIHs, while the surface hydrophobicity and average particle size of proteins decreased. Furthermore, the SPI/SPIHs-C3G interaction induced an antagonistic effect on the antioxidant capacity (ABTS and DPPH) of the complex system, with the masking effect on the ABTS scavenging capacity of the SPIHs-C3G complexes being lower than that of the SPI-C3G complexes. This study contributes to the design and development of functional beverages that are rich in hydrolysates and anthocyanins.

This study investigated the effect of ultrasound on gel properties of soy protein isolates (SPIs) at different salt concentrations. The results showed that ultrasound could significantly improve the gel hardness and the water holding capacity (WHC) of the salt-containing gel (p < 0.05). The gel presents a uniform and compact three-dimensional network structure. The combination of 200 mM NaCl with 20 min of ultrasound could significantly increase the gel hardness (four times) and the WHC (p < 0.05) compared with the SPI gel without treatment. With the increase in NaCl concentration, the ζ potential and surface hydrophobicity increased, and the solubility decreased. Ultrasound could improve the protein solubility, compensate for the loss of solubility caused by the addition of NaCl, and further increase the surface hydrophobicity. Ultrasound combined with NaCl allowed proteins to form aggregates of different sizes. In addition, the combined treatment increased the hydrophobic interactions and disulfide bond interactions in the gel. Overall, ultrasound could improve the thermal gel properties of SPI gels with salt addition.

This study evaluated the correlation between the sensory characteristics and spices of 50 commercial meat analogs and selected 4 spices to improve the flavor characteristics of soy protein concentrate (SPC) extrudates. Volatile compounds in extrudates and commercial meat analogs were investigated using headspace solid-phase microextraction and gas chromatography–mass spectrometry. The total concentrations of off-flavor volatile compounds in commercial products decreased with an increasing degree of processing. Furthermore, after adding spices during extrusion, the concentrations of volatile compounds such as aldehydes, alcohols, and furans related to thermal treatment decreased by approximately 5–39%, 5–15%, and 11–56%, respectively. Among them, compounds such as nonanal, 2-pentlyufuran, and 1-octen-3-ol, typical off-flavors in soy-based food, decreased by 8–42%, 11–55%, 2–52%, respectively. The correlation analysis between the antioxidative abilities of spices and volatile compounds showed that the contents of total phenolics were negatively correlated with the contents of ketones and alcohols in extrudates (p < 0.001). Moreover, the aroma-active compounds in extrudates were changed. More pleasant compounds, including alkanes and olefins, were observed by adding different spices as well. Especially in black pepper treated extrudates, the OAV value of off-flavor volatile compounds such as hexanal, octanal, 2-pentlyfuran decreased. In conclusion, the addition of spices can reduce off-flavor compounds related to thermal reactions, such as oxidation and the Maillard reaction, and impart newly pleasant flavors to extrudates during the extrusion of SPC. It is important to explore new methods that can be used to improve the flavor of extrudates so that consumers’ preferences of meat analog products can be improved.