Quality characteristics of soybean fermented by Mucor, Rhizopus, and Aspergillus from meju

Three candidate starter strains-Aspergillus oryzae SNU-G, Mucor sp. KACC 46077, and Rhizopus oryzae KACC 40256-were inoculated into soybean, as individual strains or in combination, to assess their roles in fermentation. All the strains increased the pH, amino-type nitrogen, and moisture content of the soybean during fermentation, and decreased the lightness, redness, and yellowness. The inoculated strains increased to an average density of 1.37 × 10⁸ spores/g (from the initial 5.0 × 10⁷ spores/g) after 20 days of fermentation. Forty-two volatile compounds, including an acid, alcohols, carbonyls, furans, and a pyrazine, were more abundant in soybean fermented with starters than in controls. A. oryzae SNU-G increased the pH more than the other strains and produced more volatile alcohol compounds. R. oryzae KACC 40256 resulted in the lowest reduction of redness and yellowness during the fermentation and produced large amounts of carbonyl compounds, including two specific volatile compounds, 2-hydroxy-3-methylcyclopent-2-en-1-one and (3E)-3-ethyl-2-methylhexa-1,3-diene. Mucor sp. KACC 46077 contributed the least to pH change and volatile compound production, and did not produce specific volatile compounds. Although no significant synergy in the production of volatile compounds was found when using mixtures of strains compared with application of single strains, the quality of fermented soybeans was confirmed to be different depending on the strain(s) applied.