The Physicochemical and Antioxidant Characteristics of a p-Coumaric Acid-Epigallocatechin Gallate-Chitosan Tyrosinase Inhibitor

As a novel tyrosinase inhibitor, p-CSPs-EGCG was prepared by grafting p-coumaric acid (p-CA) and epigallocatechin-3-gallate (EGCG) onto chitosan particles (CSPs). Its physicochemical and structural characteristics were identified using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR). Its functional properties-antioxidant activity (2, 2 '-azinobis-[3-ethylbenzothiazoline-6-sulfonicacid] [ABTS], 1-Diphenyl-2-picryl-hydrazyl [DPPH]), and tyrosinase inhibition rate were investigated. SEM showed that the spherical particle size of p-CSPs-EGCG was about 100 nm when the mass ratio of p-CSPs to EGCG was 1:2. FTIR showed that the amide of the CSPs had shifted from 1545 to 1567 cm- 1 (p-CSPs), indicating that p-CA' -COOH reacted with the CSPs' NH2. The appearance of a new peak at 2978-2895 cm- 1 in the FTIR spectrum of p-CSPs-EGCG signified that the successful reaction of EGCG's -OH with p-CSPs' NH2. p-CSPs-EGCG showed better antioxidant activity (ABTS, 80.6%; DPPH, 81.5%) than the CSPs and p-CSPs, especially given that it had higher antioxidant stability than p-CA and EGCG after 7 d's storage, with p-CA differentially decreased to 13.7% (ABTS) and EGCG to 18.8% (ABTS), while p-CSPs-EGCG barely decreased. Moreover, p-CSPs-EGCG showed stronger tyrosinase inhibition (54.1%) than the CSPs and the p-CSPs and more stable characteristics than p-CA and EGCG after 7 d's storage, with p-CA differentially decreased by 9.80% and EGCG by 16.1%, while p-CSPs-EGCG decreased by only 3.10%. It was found that prepared p-CSPs-EGCG is a reliable tyrosinase inhibitor in fresh-cut fruits and vegetables.