A time-correlated mass spectrometry (MS)-based metabolic profiling was performed for rice koji made using the substrates with varying degrees of milling (DOM). Overall, 67 primary and secondary metabolites were observed as significantly discriminant among different samples. Notably, a higher abundance of carbohydrate (sugars, sugar alcohols, organic acids, and phenolic acids) and lipid (fatty acids and lysophospholipids) derived metabolites with enhanced hydrolytic enzyme activities were observed for koji made with DOM of 5–7 substrates at 36 h. The antioxidant secondary metabolites (flavonoids and phenolic acid) were relatively higher in koji with DOM of 0 substrates, followed by DOM of 5 > DOM of 7 > DOM of 9 and 11 at 96 h. Hence, we conjecture that the rice substrate preprocessing between DOM of 5 and 7 was potentially optimal toward koji fermentation, with the end product being rich in distinctive organoleptic, nutritional, and functional metabolites. The study rationalizes the substrate preprocessing steps vital for commercial koji making.

中文翻译：

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代谢组学揭示了针对米曲发酵的最佳谷物预处理（碾磨）

基于时间相关质谱（MS）的代谢谱分析是针对使用不同研磨度（DOM）底物制成的大米曲进行的。总体上，观察到67种主要和次要代谢物在不同样品之间有明显区别。值得注意的是，在36 h时，由DOM为5–7底物制得的酒曲中，观察到碳水化合物（糖，糖醇，有机酸和酚酸）和脂质（脂肪酸和溶血磷脂）衍生的代谢产物具有较高的水解酶活性，具有较高的丰度。。曲中抗氧化剂的次级代谢产物（类黄酮和酚酸）相对较高DOM为0的底物，然后在96 h时的DOM为5> DOM的7> DOM的9和11。因此，我们推测DOM介于5和7之间的大米底物预处理对于曲发酵而言可能是最佳的，其终产物富含独特的感官，营养和功能性代谢产物。该研究合理化了对商业曲制备至关重要的底物预处理步骤。