Free-amino acid profiles of thua nao, a Thai fermented soybean
Dajanta, K., Apichartsrangkoon, A., Chukeatirote, E. and Frazier, R. A. (2011) Free-amino acid profiles of thua nao, a Thai fermented soybean. Food Chemistry, 125 (2). pp. 342-347. ISSN 0308-8146
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To link to this article DOI: 10.1016/j.foodchem.2010.09.002
Thua nao, a rich source of free-amino acids, is a fermented soybean, usually used as seasoning or flavouring enhancer in northern Thailand. Free-amino acids (FAA) of unfermented/cooked soybeans, thua nao, fermented by pure Bacillus subtilis TN51 (TNB51), and a naturally fermented product (TNMX), were investigated by pre-column derivatisation with 9-fluorenylmethyl chloroformate, followed by reversed-phase HPLC. Total FAA and essential amino acids were found at significantly higher concentrations in TNB51 thua nao than in TNMX thua nao (naturally fermented). Both fermented thua nao had much higher concentrations of FAA than had their unfermented counterparts. With respect to taste-enhancing FAA, typical bitter attributes of thua nao came mainly from hydrophobic and basic FAA, whereas an umami attribute came predominantly from acidic FAA.