FORMATION AND REDUCTION OF VOLATILE SULFU R-CONTAINING-COMPOUNDS IN SYNTHETIC MEDIA BY SALT-TOLERANT YEASTS

By using a synthetic medium containing 18 amino acids as a nitrogen so urce, volatile sulfur-containing compounds formed and reduced by salt- tolerant yeasts and a sake yeast were studied. As the test yeasts, Zyg osaccharomyces rouxii S84 (Z. rouxii), Candida versatilis D-5, both sa lt-tolerant and isolated from red salty kome mise, and Saccharomyces c erevisiae RIB 6002 (Kyokai no. 7), a salt-sensitive sake yeast, were e mployed. These yeasts were cultured in a stationary manner at 30 degre es C until they had consumed nearly all the glucose used as a carbon s ource. The volatile sulfur-containing compounds in the non-inoculated and cultured media were identified by GC and GC-MS after they had been collected on a Tenax TA using an apparatus for trapping headspace vol atiles. The volatile sulfur-containing compounds commonly found both i n the non-inoculated and cultured yeast media were identified as dimet hyl disulfide, dimethyl trisulfide and 3-(methylthio)propionaldehyde ( methional). Further, in the cultured yeast media, in addition to these compounds, the formation of 3-(methylthio)propyl acetate and 3-(methy lthio)-1-propanol (methionol) was observed. The amounts of dimethyl di sulfide, dimethyl trisulfide and methional contained in the cultured y east media were found to decrease as little as 0.6-85.1% compared to t hose in the non-inoculated media. The rate of decrease of these compou nds in the cultured media was greatest in Z. rouxii among the tested y easts. In particular, in the cultured medium containing salt, in spite of the fact that the consumption rate of glucose was low and it had p oor development, Z. rouxii eliminated these compounds by as much as 55 .2-99.4%. The formation and reduction of these volatile sulfur-contain ing compounds by Z. rouxii were also observed both in the non-inoculat ed and cultured media containing methionine as the sole nitrogen sourc e. In addition to these compounds, ethyl 3-(methylthio)propanoate was formed by Z. rouxii.