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β-Carotene (β-C) is a well-established natural antioxidant agent, but its poor water-solubility, low chemical stability and low bioavailability limit its application in food, pharmaceuticals and cosmetics industries. Thus it is critical to develop an efficient method to improve the water solubility and stability of β-C. In this research, amphiphilic chitosan-graft-poly (lactide) (CS-g-PLA) copolymer was synthesized via a homogeneous ring-opening polymerization (ROP) in ionic liquid. The obtained CS-g-PLA copolymer was able to self-assemble into about 14 nm micelles in water at low concentration, and β-C loaded micelles (β-C/M) had low β-C degradation after 15 days. The antioxidant properties of the β-C/M were investigated by the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) method and ferric reducing antioxidant power (FRAP) method, respectively. Significantly improved antioxidant activity was observed for β-C/M in compare with free β-C. The aqueous dispersion of β-C/M has potential to be applied in the field of functional food and cosmetics. [ABSTRACT FROM AUTHOR]

• An antioxidant amphiphilic chitosan water-soluble derivative (CS- graft -ALA) was prepared. • CS- graft -ALA could self-assemble into nanosized micelles in water. • Hydrophobic quercetin was successfully encapsulated in CS- graft -ALA micelles leading to enhanced antioxidant activity. • CS- graft -ALA nanomicelles could significantly improve the photostability and thermal stability of quercetin. Natural active compounds with antioxidant properties and other potential health benefits, like quercetin (Qu), have aroused wide concern for developing bio-functional products. However, their applications are hindered by their intrinsic poor water solubility and chemical instability. In this paper, a natural antioxidant alpha lipoic acid (ALA) was grafted onto chitosan (CS) to synthesize a novel graft polymer (CS-graft-ALA). In particular, this graft-polymer could self-assemble into spherical nanomicelles in water, with a low critical micelle concentration (CMC) of 0.0076 mg/mL. As a robust and active nanocarrier, the CS-graft-ALA micelles showed high efficiency in encapsulating Qu and dispersing Qu in water. As found, the antioxidant activity of Qu was effectively enhanced when entrapped within CS-graft-ALA micelles. Moreover, CS-graft-ALA micelles could significantly improve the photo-stability and temperature-stability of Qu. The Qu/CS-graft-ALA micelles with excellent water dispersability, stability and improved antioxidant activity hold a great potential for wide applications. [ABSTRACT FROM AUTHOR]