Raspberry fruit samples (4 g) were homogenized in 8.0 ml ice
cold, degassed 7.57 mM sodium ascorbate solution with cold mortar and pestle under N2 at 0
C. The homogenate was filtered through four layers of miracloth and centrifuged at 30,000 g for 15 min at 0
C. The supernatant was deproteined by incubation in a water bath at 100
C for 3 min and then centrifuged at 15,000 g for 15 min at 0
C. The supernatants were used for the GSH and GSSG assays. GSH and GSSG enzyme were assayed using the method of Castillo and Greppin (1988). GSSG was calculated by subtraction of GSH from total glutathione.