Levels of Glutathione and Activities of Related Enzymes During Ripening of Koshu and Cabernet Sauvignon Grapes and During Winemaking

¹ The Institute of Enology and Viticulture, Yamanashi University, 13-1 Kitashin 1-chome, Kofu, Yamanashi 400-0005, Japan.

The glutathione content of berries and wines and the activities of six enzymes related to glutathione metabolism were investigated during the ripening of Koshu and Cabernet Sauvignon grapes and during winemaking from the two varieties. In general, changes associated with ripening were similar in both. The glutathione content in berries increased during ripening, and over 90% of it was reduced. The highest levels of reduced glutathione were 107 and 69 nmol/g fresh weight of Koshu and Cabernet Sauvignon grapes, respectively. Catalase, nonspecific peroxidase, and ascorbate peroxidase activities were undetectable in grapes of either cultivar during ripening, but glutathione reductase, dehydroascorbate reductase, and glutathione peroxidase activities were detected in both. Dehydroascorbate reductase showed a high level of activity (0.03 U/g fresh weight) during berry ripening, but the activity rapidly disappeared at 18° to 19° Brix. The levels of glutathione reductase and glutathione peroxidase were low or absent until 18° to 19° Brix, after which they increased. These enzyme activities may indicate maturity of the grape berry. During winemaking, the activities of glutathione peroxidase and dehydroascorbate reductase decreased but glutathione reductase showed increased activity in both wines, which was probably derived from yeast.

Key words: glutathione, redox state, oxidation

Submitted on September 8, 1998
Revised on March 5, 1999