Effects of Starter Candidates and NaCl on the Production of Volatile Compounds during Soybean Fermentation

Abstract

We inoculated different combinations of three starter candidates of Bacillus licheniformis, <i>Staphylococcus succinus</i>, and <i>Tetragenococcus halophilus</i>, into sterilized soybeans to predict their contributions to volatile compounds production through soybean fermentation. Simultaneously, we added NaCl to soybean cultures to evaluate its effect on the volatile compounds profile. Cells in soybean cultures (1.5% NaCl) reached almost their maximum growth in a day of incubation, while cell growth was delayed by increasing NaCl concentration in soybean cultures. The dominance of <i>B. licheniformis</i> and <i>S. succinus</i> in the mixed culture of three starter candidates switched to <i>T. halophilus</i> as the NaCl concentration increased from 1.5% to 14% (w/w). Seventeen volatile compounds were detected from the control and starter candidate-inoculated soybean cultures with and without the addition of NaCl. Principal component analysis of these volatile compounds concluded that <i>B. licheniformis</i> and <i>S. succinus</i> made major contributions to producing a specific volatile compound profile from soybean cultures where both species exhibited good growth. 3-Hydroxybutan-2-one, butane-2,3-diol, and 2,3,5,6-tetramethylpyrazine are specific odor notes for <i>B. licheniformis</i>, and 3-methylbutyl acetate and 2-phenylethanol are specific for <i>S. succinus</i>. Octan-3-one and 3-methylbutan-1-ol were shown to be decisive volatile compounds for determining the involvement of <i>S. succinus</i> in the soybean culture containing 7% NaCl. 3-Methylbutyl acetate and 3-methylbutan-1-ol were also produced by <i>T. halophilus</i> during soybean fermentation at an appropriate level of NaCl. Although <i>S. succinus</i> and <i>T. halophilus</i> exhibited growth on the soybean cultures containing 14% NaCl, species-specific volatile compounds determining the directionality of the volatile compounds profile were not produced.