Abstract
Rice koji, used as a starter for maximizing fermentation benefits, produces versatile end products depending on the inoculum microbes used. Here, we performed metabolite profiling to compare rice koji fermented with two important filamentous fungus, Aspergillus oryzae and A. cristatus, during 8 days. The multivariate analyses showed distinct patterns of primary and secondary metabolites in the two kojis. The rice koji fermented with A. oryzae (RAO) showed increased α-glucosidase activity and higher contents of sugar derivatives than the one fermented with A. cristatus (RAC). RAC showed enhanced β-glucosidase activity and increased contents of flavonoids and lysophospholipids, compared to RAO. Overall, at the final fermentation stage (8 days), the antioxidant activities and anti-aging effects were higher in RAC than in RAO, corresponding to the increased metabolites such as flavonoids and auroglaucin derivatives in RAC. This comparative metabolomic approach can be applied in production optimization and quality control analyses of koji products.
Highlights
Different metabolomes of rice koji samples inoculated with A. cristatus or A. oryzae were compared using multivariate analysis according to the GC–MS and LC–MS data set
The principal component analysis (PCA) score plot obtained from the UHPLC–LTQ–OrbitrapMS/MS and GC–TOF–MS revealed a total variance of 40.9% (PC1, 22.01%; PC2, 18.89%)
Rice koji showed the production of different metabolites and bioactivities according to different Aspergillus species used
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Fermentation, which has a history of thousands of years, is increasingly being recognized as a method of enhancing nutrition and bioactivities of food products, in addition to processing and preserving them [1]. Rice koji is made by solid-state fermentation using steamed rice grains inoculated with microorganisms to secrete enzymes and produce beneficial metabolites. Various attempts to create delicate fermentation conditions have led to advanced fermentation efficacy and better food palatability [2,3]
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