Tenmilliliters of juice was centrifuged at 2063×g at 25 °C for 10 min,
the supernatant was collected and the absorbance at 660 nm was measured
using a spectrophotometer (UV-726 Shimadzu, Shanghai, China)
at 20±1 °C with a 1 cm path length cell, as described by Chandler and
Robertson (1983).