Volatile profiles of thua nao, a Thai fermented soy product

Thua nao, a Thai traditional fermented soybean has a unique odour due to the presence of several volatile components. In this investigation, the cooked non-fermented soybeans and soybean (thua nao) fermented by pure Bacillus subtilis TN51 (TNB51) and naturally fermented soybean (TNMX) were analysed for odour components by GC–MS, using the PDMS-SPME head space technique. The quantities of total volatiles in both TNB51 and TNMX were analogous, but the major volatile classes present in TNB51 and TNMX were pyrazines and ketones, respectively. The predominant volatiles in pure Bacillus-fermented thua nao included 2,5-dimethylpyrazine, 2-methylbutanoic acid, 2,3,5-trimethylpyrazine, 2-methylpropanoic acid and acetic acid, whereas the major volatiles in the naturally fermented soybean included 2,5-dimethylpyrazine, benzaldehyde, 5-methyl-3-hexanone, 2-butanone and 3-methyl-2-pentanone. In total, 85 volatile compounds were detected.