Hydrogen sulphide production by Saccharomyces cerevisiae UCD 522 in a synthetic grape juice medium deficient of thiamin (vitamin B1 ) and/or pyridoxine (vitamin B6 ).

The impacts of thiamin and pyridoxine along with YAN on alcoholic fermentation and hydrogen sulphide production by Saccharomyces cerevisiae were studied. Using a synthetic grape juice medium, three fermentation trials were conducted; (i) 2 × 3 factorial design with thiamin (0, 0·2, or 0·5 mg l-1 ) and YAN (60 or 250 mg l-1 ) as variables, (ii) 2 × 3 factorial design with pyridoxine (0, 0·25, or 0·5 mg l-1 ) and YAN (60 or 250 mg l-1 ) as variables, and (iii) 3 × 3 factorial design with thiamin (0, 0·2 or 0·5 mg l-1 ) and pyridoxine (0, 0·25 or 0·5 mg l-1 ) as variables in media containing 60 mg l-1 YAN. Although the progress of fermentations was affected by thiamin or pyridoxine, YAN had a larger impact than either vitamin. H2 S production was significantly lower with increasing amounts of thiamin in those fermentations under low YAN (60 mg l-1 ) while even lower amounts (<30 µg l-1 ) were produced under high YAN (250 mg l-1 ) with or without the vitamin. The highest amounts of H2 S were synthesized in those fermentations without any pyridoxine (>110 µg l-1 ), with the lowest production in media with pyridoxine and high YAN (<20 µg l-1 ). SIGNIFICANCE AND IMPACT OF THE STUDY: Concentrations of thiamin, pyridoxine and yeast assimilable nitrogen (YAN) influenced the synthesis of hydrogen sulphide (H2 S) by Saccharomyces cerevisiae in a synthetic grape juice medium. With a few exceptions, an increase in the concentration of either vitamin or YAN resulted in less H2 S released. This is the first report to demonstrate that both thiamin and pyridoxine along with YAN affected H2 S production, emphasizing the need to assess yeast nutrients to lower risks of off-odours during fermentation.