Deep eutectic solvent as a new green and safe solvent system has attracted more and more attention in recent years. In this study, three deep eutectic solvents (DES) were combined with ultrasound irradiation to extract tea polysaccharides (TPs) from Anji white tea, which was compared with conventional hot water extraction (HW). The physicochemical, structural, and biological properties of TPs extracted by ultrasound-assisted DES and hot water (HWP) were further investigated. Results showed that the DES system composed of choline chloride and 1,6-hexanediol (CH) with the molar ratio of 1:2 exhibited the optimal extraction yield (19.18%) and in vitro antioxidant activities for TPs (CHP). Furthermore, compared to the HWP, the CHP had a higher extraction yield and total carbohydrate content and a lower molecular weight. Monosaccharide composition analysis displayed that the molecular structure of CHP exhibited more arabinose but less glucose, mannose, galacturonic acid, and glucuronic acid than HWP. Little difference was observed in the preliminary structural characteristics between HWP and CHP from Fourier transform infrared analysis. Besides, CHP possessed better α-glucosidase inhibitory and hypoglycemic activity in L6 cells than HWP. Therefore, the ultrasound-assisted DES extraction method can be a promising strategy for extracting TPs with excellent bioactivities for future applications in functional foods.

Plant protein can be functionally strengthened by its modification into amyloid fibrils, which has drawn growing interest. In this study, we investigated the effects of ultrasonic pretreatment on the fibrillation kinetics, physicochemical properties, and functional aspects of soy protein isolate amyloid fibrils (SPF). Firstly, soy protein isolates (SPI) were subjected to ultrasonic pretreatment by regulating time and power under neutral conditions. Subsequently, the pretreated SPI was converted into SPF through acidic heating. The results indicated that ultrasonic pretreatment significantly improved surface hydrophobicity and solubility of SPI through ultrasound's cavitation and thermal effects. Thioflavin T fluorescence assay revealed SPF40 (450 W, 40 min) had the fastest growth rate, 104.23 % higher than SPF0 (without ultrasonic pretreatment), while SPF10 (450 W, 10 min) had the highest fibril yield, 20.97 % higher than SPF0. Physicochemical analysis showed that ultrasonic pretreatment accelerated the formation of SPF from SPI by exposing the surface hydrophobic groups, lowering the zeta potential, breaking down original fibrils into shorter fibrils, and altering the secondary structure from α-helices into β-sheets. Morphological examination by transmission electron microscopy exhibited a higher maturation state, showing more rigid and straight fibrils structure in SPF10 compared to SPF0. Functionally, SPF with ultrasonic pretreatment had higher emulsifying activity than SPI and SPF0. Rheological analysis further confirmed SPF emulsions' better mechanical strength over SPI emulsions. Overall, this study demonstrates that ultrasonic pretreatment is an effective way to enhance the formation and properties of SPF, which can be further applied to developing advanced protein products and novel functional food systems.