Chemical Changes of Some Important Sulfur-Containing Compounds
We have used an HPLC method to assay reduced and oxidized glutathione and cysteine in musts and wines. This method is based on carboxymethylation with iodoacetic acid followed by derivatization of the amino groups with 2,4-dinitro-l-fluorobenzene. During the 1995 season we implemented the procedure and have accomplished the following. We can derivatize and separate reduced glutathione and cysteine in grape juices. Using this method we have determined the level of glutathione and cysteine in Chardonnay berries. In berries harvested at 22.5 Brix we determined that the amount of glutathione present before crushing was 214 nmoles/g fresh weight and the amount of cysteine was 12.16 nmoles/g fresh weight. This gives a ratio of glutathione to cysteine of 17.6 showing that glutathione is more than 17 times as abundant as cysteine in Chardonnay berries prior to crushing. In wines only oxidized glutathione was detected. Reduced glutathione and cysteine, and oxidized cysteine were not found in wines. Wines to which oxidized glutathione had been added were less brown than reference wine. Aroma difference testing of wines to which oxidized glutathione was added to give 30 times the normal were not different from reference wines at the 95%level. We initiated experiments to determine the sensory effects of adding glutathione to musts prior to fermentation. Preliminary results indicate that musts to which glutathione has been added ferment more quickly than the control fermentations without glutathione.