Effects of non-covalent binding of different proteins and apple polyphenols on structure and functional properties

Abstract

Apple polyphenols (AP) exhibit diverse biological activities but have limited bio-accessibility, while plant proteins often suffer from poor solubility, limiting their functional properties. Therefore, there is a significant research interest in synergistically enhancing the bio-accessibility of AP and improving the functional characteristics of plant proteins. In this study, soy protein isolate (SPI), whey protein isolate (WPI), chickpea protein (CP), and tartary buckwheat protein (TBP) were utilized to synthesize AP-protein complexes through non-covalent binding with AP. Structural characterization found that the polyphenol contents were as follows: TBP-AP > CP-AP > SPI-AP > WPI-AP. Multi-spectral analysis indicated that AP altered the secondary structures of the four proteins, are reduced their surface hydrophobicity. In vitro, antioxidant activity assessments demonstrated that polyphenols significantly enhanced the antioxidant capacity of the proteins. AP-protein complexes protected against H₂O₂-induced oxidative stress in HepG2 cells, and restored antioxidant enzyme activity (WPI-AP > TBP-AP > SPI-AP > CP-AP). Furthermore, it enhanced α-amylase and α-glucosidase inhibition, demonstrating the potential to regulate blood sugar levels. In simulated digestion models, the sequence of TBP-AP > WPI-AP > CP-AP > SPI-AP effectively protected AP from delayed release in the intestinal phase, thereby enhancing the bio-accessibility of AP. This study not only identifies the optimal synergistic interaction between AP and TBP but also provides new insights into enhancing the bioavailability of AP and effectively replacing animal protein application with plant proteins for potential high-value utilization of AP and plant proteins.