Wei-Cai Zeng

Effects of non‐covalent interactions between tea polyphenols (TPs) and soybean protein isolate (SPI) on the structural and functional properties of soy protein gels were investigated, and the potential action mechanism was further explored. SPI was firstly non‐covalent bound with TP to form the SPI–TP gel, and its structural characteristics, physicochemical properties, rheological properties, and digestion properties were determined. TP exhibited the strong capability to form hydrogen bonds and/or hydrophobic interactions with SPI, which was concentration‐dependent. Moderate addition of TP could effectively regulate the strength of different interactions in gel, such as interactions of proteins and interactions between proteins and water molecules, thereby yielding gels with good gel strength and hydration capacity. With increase of addition concentration, TP showed the capability to induce protein structural unfolding and formed new non‐covalent interactions with proteins, which facilitated the formation of a more robust and uniform gel network, thereby improving gel's properties. However, excessive addition of TP caused the excessive cross‐linking of protein, ultimately compromising gel strength and structural stability. Additionally, during in vitro digestion, the addition of TP reduced the digestion of protein in gel but significantly enhanced the antioxidant properties of the digesta. All results suggest that TPs have the potential to effectively regulate the structure and function of SPI gels, which provides the theoretical guidance and research foundations for the application of protein–polyphenol complexes as functional food ingredients or biomaterials in food and chemical industries.

In the present study, the effects of longan peel and seed on the quality of longan cake were determined, and the effects of longan peel extract (LPE) and longan seed extract (LSE) on the physicochemical properties of wheat starch were also measured. Furthermore, the phenolic profile and antioxidant activities of these extracts were observed. The results showed that both longan peel and seed could improve the color, texture, and volatile flavor compounds of longan cake. In addition, the properties of wheat starch, including gelatinization characteristics, thermogravimetric analysis, rheological properties, solubility, swelling power, water/oil-holding capacity and iodine binding ability, were all affected by LPE and LSE significantly. Both LPE and LSE had high contents of total phenols (LPE: 71.05 ± 2.57 mg/g, LSE: 78.49 ± 5.21 mg/g) and total flavonoids (LPE: 286.27 ± 6.04 mg/g, LSE: 423.21 ± 7.69 mg/g). Gallic acid, ellagic acid, and ellagic acid 4-O-α-l-arabinofuranoside were identified as the main phenolic compounds of LPE, while those of LSE were gallic acid, ellagic acid, ellagic acid 4-O-α-l-arabinofuranoside and (-)-epicatechin. Furthermore, LPE and LSE both exhibited good antioxidant activities to scavenge free radicals and showed high reducing power. All results suggest that longan peel and seed are rich in phenols and can improve the properties of starch so as to enhance the quality of starch product, which shows their potential application in food and chemical industries.