Lipoxygenase activity and browning formation of lychee in syrup after high pressure and canning processes

Abstract

This study aimed to evaluate the effect of high pressure (200, 400 and 600 MPa at 25°C for 10 and 20 min) and canning (100°C for 18 min) processes on lipoxygenase (LOX) activity and browning formation of lychee in syrup. Results showed that the pH profile of LOX activity in lychee was bell-shaped with a maximum activity around pH 4.0. After pressurization, the activities of LOX in lychee flesh apparently diminished with the increasing the pressure levels and processing times, in particular at a pressure of 600 MPa for 10 and 20 min the decreases in activity were 86% and 89%, respectively. For lychee in syrup, LOX was completely inactivated in canned sample, whereas the residual activities in pressurized batches as treated at 200-600 MPa for 20 min were ranged of 18-88%. In addition, pressurized samples depicted much lower browning index than that canned product, since heated lychee extract resulted in the pink color formation with a maximum absorption at 544 nm.