Preparation of Koji Using Aspergillus oryzae and a Halophilic Aromatic Yeast
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Abstract:
A halophilic aromatic yeast (Zygosaccharomyces rouxii) was added to Aspergillus oryzae and their synergistic effect on the preparation of koji was explored in terms of the metabolic regulation of yeast with enzymatic systems, physicochemical indices, and volatile compounds. Changes in the numbers of the yeast colonies and Aspergillus oryzae spores, the activity of the enzymatic systems, and physicochemical indicators during the preparation of koji were dynamically monitored, while the volatile components of the finished product were analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that when the amount of yeast added was approximately 1.5 × 106 yeast/g koji and the inoculum size of Aspergillus oryzae was 0.15% (m/m), the number of Aspergillus oryzae spores did not significantly change and the neutral protease activity was 3100 U/g at 36 h, which was comparable to the results obtained for the control group. However, α-amylase activity decreased by 22% and saccharifying enzyme activity increased by 7% in the yeast-inoculated group, while aminopeptidase and acidic carboxypeptidase activities did not exhibit significant difference compared to the results obtained in the control group. After the preparation of koji was complete, the concentrations of amino nitrogen and reducing sugar were almost the same for the yeast-inoculated and control groups, while the organic acid content of the yeast-inoculated sample was lower than that of control. There were 32 and 23 volatile components identified by GC-MS in the yeast-inoculated and control groups, respectively. Comprehensive analysis showed that inoculation of a halophilic aromatic yeast during the preparation of koji did not show a significant effect on the enzymatic system and growth of Aspergillus oryzae; however, it improved the flavor and quality of the finished koji.
