Unraveling the effect of ultrasound-assisted alkali treatment on β-lactoglobulin-flavonoids covalent complex system formation and its potential for lipophilic bioactive compounds delivery.

The limited water solubility and poor bioavailability of curcumin (Cur) and lycopene (Lyc) significantly restrict their use in food-related applications. Therefore, the development of various delivery systems to enhance Cur/Lyc solubility and bioavailability is essential. This study focuses on the formation of covalent complex of β-lactoglobulin (β-Lg) with six flavonoids (apigenin (API), luteolin (LUT), myricetin (MY), apigenin-7-O-glucoside (AGL), luteolin-7-glucoside (LGL), and myricitrine (MYR)) by ultrasound-assisted alkali treatment and construction of functional delivery system. The results showed that ultrasonic treatment and covalent interaction were beneficial for the covalent binding of β-Lg to flavonoids, and enhanced the hydrophilicity (Ho value decreased by 25.14 %), thermal stability (T value increased by 10.60 %), and antioxidant activity (DPPH value increased by 84.63 %) of U-β-Lg-MY complexes. The number of hydroxyl groups and glycosidic sites of these flavonoids affected the structure and functional properties of β-Lg-flavonoid complexes. Among them, β-Lg-MY has good functional properties and can be used as a stable delivery system. Cur and Lyc stability significantly improved using U-β-Lg-MY covalent complex to deliver them, and the loading efficiency was increased by 21.32 % and 20.68 %, respectively. It was proved that U-β-Lg-MY has the effect of release of Cur and Lyc.