In this study, 34 yeast isolates were obtained fromkoji andmoromi samples of Thai soy sauce fermentation. However,
the most interesting yeast strain was isolated from the enriched 2 month-old (M2) moromi sample and
identified as Meyerozyma (Pichia) guilliermondii EM2Y61. This strain is a salt-tolerant yeast that could tolerate
up to 20% (w/v) NaCl and produce extracellular and cell-bound glutaminases. Interestingly, its glutaminases
were more active in 18% (w/v) NaCl which is a salt concentration in moromi. The extracellular glutaminase's
activity was found to be much higher than that of cell-bound glutaminase. The highest specific activity and
stability of the extracellular glutaminase were found in 18% (w/v) NaCl at pH 4.5 and 37 °C. A challenge test by
adding partially-purified extracellular glutaminase from M. guilliermondii EM2Y61 into 1 month-old (M1)
moromi sample showed an increased conversion of L-glutamine to L-glutamic acid. This is the first report of
glutaminase producing M. guilliermondii isolated from the moromi of Thai soy sauce fermentation. The results
suggested the potential application of M. guilliermondii EM2Y61 as starter yeast culture to increase L-glutamic
acid during soy sauce fermentation.