Impact of thiamine and pyridoxine on alcoholic fermentations of synthetic grape juice

by 1978- Xing, Huajing

by Huajing Xing, M.S. Washington State University August 2007 Chair: Charles G. Edwards Sluggish fermentation and H2S production are serious problems found in the wine industry since they are directly related to wine quality and economic issues. There are several factors that can cause these problems, such as nitrogen and vitamin deficiencies. In this study, the effects of thiamine (vitamin B1) and pyridoxine (vitamin B6) on alcoholic fermentation rates and hydrogen sulfide (H2S) production were studied. Using a synthetic grape juice base, three fermentations were conducted: (1) a 2 × 3 factorial design with nitrogen (60 and 250 mg/L) and thiamine (0, 0.2, and 0.5 mg/L) as variables with a sufficient concentration of pyridoxine (2 mg/L), (2) a 2 × 3 factorial design with nitrogen (60 and 250 mg/L) and pyridoxine (0, 0.25, and 0.5 mg/L) as variables with a sufficient concentration of thiamine (0.5 mg/L), and (3) a 3 × 3 factorial design for comparing the effects of thiamine (0, 0.2, and 0.5 mg/L) and pyridoxine (0, 0.25, and 0.5 mg/L) at the low concentration of nitrogen (60 mg/L). Fermentations were conducted with Saccharomyces cerevisiae UCD 522 at 22oC. Thiamine, pyridoxine, nitrogen and their interactions were found to affect fermentation rate and H2S production. At low levels of thiamine and pyridoxine, yeast iv exhibited slower fermentation rate regardless of nitrogen concentration, which indicated that thiamine and pyridoxine deficiencies may cause sluggish fermentations. Hydrogen sulfide production was significantly different (p ? 0.001) at different concentrations of thiamine and pyridoxine. Furthermore, interactions between thiamine, pyridoxine and nitrogen also highly affected hydrogen sulfide production. Sensory evaluation methods were applied to the synthetic wine samples fermented at different thiamine, pyridoxine and nitrogen concentration combinations and hydrogen sulfide was found to be significant different in aroma attribute rating. By adjusting thiamine, pyridoxine and nitrogen concentrations in grape juice, sluggish fermentation and excessive hydrogen sulfide production can be reduced. v