Colour measurement
The colour of grape juice was measured using a Minolta colorimeter
(CS-100A, Minolta Co., Ltd, Japan) according to Du et al.
(2012) with slight modifications. The degree of browning in the
grape juice was expressed by the percent decrease in the L value
calculated by subtracting the L value of treated and control samples
measured at evaluation time from the time zero L value obtained
from control samples measured immediately after juicing,
divided by the time zero value and multiplied by 100.