Abstract
Aspergillus oryzae has been commonly used to make koji, meju, and soy sauce in traditional food fermentation industries. However, the metabolic behaviors of A. oryzae during fermentation in various culture environments are largely uncharacterized. Thus, we performed time resolved (0, 4, 8, 12, 16 day) secondary metabolite profiling for A. oryzae KCCM 12698 cultivated on malt extract agar and broth (MEA and MEB) under solid-state fermentation (SSF) and submerged fermentation (SmF) conditions using the ultrahigh performance liquid chromatography-linear trap quadrupole-ion trap-mass spectrometry (UHPLC-LTQ-IT-MS/MS) followed by multivariate analyses. We observed the relatively higher proportions of coumarins and oxylipins in SSF, whereas the terpenoids were abundant in SmF. Moreover, we investigated the antimicrobial efficacy of metabolites that were extracted from SSF and SmF. The SSF extracts showed higher antimicrobial activities as compared to SmF, with higher production rates of bioactive secondary metabolites viz., ketone-citreoisocoumarin, pentahydroxy-anthraquinone, hexylitaconic acid, oxylipins, and saturated fatty acids. The current study provides the underpinnings of a metabolomic framework regarding the growth and bioactive compound production for A. oryzae under the primarily employed industrial cultivation states. Furthermore, the study holds the potentials for rapid screening and MS-characterization of metabolites helpful in determining the consumer safety implications of fermented foods involving Koji mold.
Highlights
Aspergillus species are a ubiquitous mold, which widely affects human life in both deleterious and beneficial ways, since some species are pathogens and the others are used to make fermented foods (Kang et al, 2013)
Multivariate analyses including the unsupervised principle component analysis (PCA), as well as the supervised partial least squares discrimination analysis (PLS-DA) were performed to select the discriminant metabolites adding to the observed variance
The PLS-DA score plots based on UHPLC-LTQ-IT-mass spectrometry (MS)/MS profiling data in negative ion mode showed distinct metabolomic patterns between solid-state fermentation (SSF) and submerged fermentation (SmF) along PLS1 (23.68%) and PLS2 (9.02%) components (Figure 1B)
Summary
Aspergillus species are a ubiquitous mold, which widely affects human life in both deleterious and beneficial ways, since some species are pathogens and the others are used to make fermented foods (Kang et al, 2013). Metabolomics studies of fermented food under different culture conditions have highlighted distinct profiles of metabolites owing to differences in microbial consortia and metabolism (Oh et al, 2016; Lee et al, 2017). The dynamics of microbial communities vary spatiotemporally in a variety of fermentative systems, which have been investigated to determine the quality of end-products (Chen et al, 2014; Yang et al, 2016b). These studies have suggested that A. oryzae is among the dominant mold varieties in both the natural as well as the in situ cultivated microenvironments i.e., fermented foods
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