Formation, physiochemical stability, and bioaccessibility of quercetin-loaded α-lactalbumin amyloid-like fibril nanocomposite with ultrasound and its application in yogurt

Food protein-based amyloid-like fibrils have been utilized recently to stabilize, encapsulate and increase the water solubility, chemical stability and bioaccessibility of labile and hydrophobic nutrients because of their unique structure (high aspect ratio and nanoscale size) endowing exceptional performance. In this study, formation mechanism of α-lactalbumin fibrils with acid-heat treatment was assessed with such as sodium dodecyl sulfate polyacrylamide gel electrophoresis, thioflavin T fluorescence spectroscopy, and Congo red UV-vis spectroscopy. Mature α-lactalbumin fibrils with a width of 10-15 nm and a length of 0.5-2.0 μm were attained with a 24 h acid-heat treatment (pH 2.0, 85°C). α-Lactalbumin self-assembled into α-lactalbumin fibrils mainly through hydrophobic interactions and hydrogen bonding. Compared with α-lactalbumin (native), the water solubility of quercetin in α-lactalbumin fibrils nanocomposites was markedly enhanced. Ultrasound further increased its water solubility. Quercetin-loaded α-lactalbumin fibrils with ultrasonication exhibited the highest antioxidant activity probably due to the highest loading amount of quercetin. Compared with quercetin (free), the bioaccessibility of quercetin in α-lactalbumin fibrils with ultrasound was increased to 24.85% (a 2.16-fold increase). The incorporation of quercetin-loaded α-lactalbumin fibrils nanocomposites exhibited no pronounced impacts on the stability of yogurt and remarkably enhanced the perception score of overall assessment, as illustrated with sensory evaluation. The finding demonstrates that quercetin-loaded α-lactalbumin fibrils nanocomposites can be used as functional supplements in food system.