FORMATION OF VOLATILE COMPOUNDS DURING BACILLUS-SUBTILIS FERMENTATIONOF SOYA BEANS

The formation of volatile compounds during the Bacillus subtilis ferme ntation of cooked, roasted soya bean cotyledons was investigated. The materials examined were: dry roasted cotyledons; autoclaved, roasted c otyledons; and autoclaved, roasted cotyledons fermented for 18 h and 3 6 h at 35 degrees C. Growth of B subtilis led to the formation of many volatile compounds. The volatile compounds formed in the largest amou nts during fermentation were 3-hydroxy-2-butanone (acetoin), 2,5-dimet hylpyrazine and trimethylpyrazine. Compounds present at concentrations exceeding their odour threshold values included nonanal, decanal, 1-o cten-3-ol, butanedione, 3-hydroxy-2-butanone, 3-octanone, 2,5-dimethyl pyrazine, 3,6-dimethyl-2-ethylpyrazine, 2-pentylfuran, dimethyl sulfid e, benzaldehyde and 2-methoxyphenol. Compounds found in 18 h fermented cotyledons which were absent, or present in much lower concentrations , in roasted or autoclaved cotyledons included several aliphatic keton es, acetic acid, two aliphatic esters, several pyrazines, 2-pentylfura n, dimethyl sulphide, 2-methoxyphenol and trimethyloxazole. The total mass of volatile compounds present after 36 h incubation was less than half that present after 18 h. This was mainly due to the disappearanc e of 3-hydroxy-2-butanone, 2,5-dimethylpyrazine and 2,6-dimethylpyrazi ne. The biogenesis of the volatile compounds is discussed.