Chemical Changes of Some Important Sulfur-Containing Compounds During Crushing, Fermentation and Storage

We have adapted an enzymatic glutathione disulfide (GSSG) analysis for use in wine. In the course of adapting this procedure we discovered that wine contains an inhibitor of glutathione reductase. Since this enzyme is critical for the assay, the inhibitor would interfere with the analysis. We found that the inhibitor could be removed by treating the wine with polyvinylpolypyrrolidone (PVPP). After PVPP treatment GSSG can be assayed in wines. It appears that the inhibitor is a phenolic compound commonly present in wines. We analyzed wines made during the 1994 season. The GSSG content ranged from a low of 0.76 mg/1 in a Chenin Blanc to 12.1 mg/1 in a Thompson Seedless wine. We believe that this is the first demonstration of GSSG in wines. Oxidized glutathione may be an important source of reduced sulfur in wines that could serve as precursor to disulfides that have been identified in wines having off aromas. We conducted an aging study in which cysteine, GSH and GSSG were added to wines. The wines with cysteine, GSH and GSSG all exhibited less browning during 120 days of aging. Wines with added cysteine (100 and 300 mg/L) had distinctive hydrogen sulfide type aromas while wines with GSH or GSSG had less of this characteristic. Work with cysteine indicates that cysteine behaves similar to glutathione during berry crushing and aging Thus, cysteine disulfide may be present in wines. Additional work is underway to determine if cysteine disulfide can be detected in wines