Abstract
Rice koji, used early in the manufacturing process for many fermented foods, produces diverse metabolites and enzymes during fermentation. Using gas chromatography time-of-flight mass spectrometry (GC-TOF-MS), ultrahigh-performance liquid chromatography linear trap quadrupole ion trap tandem mass spectrometry (UHPLC-LTQ-IT-MS/MS), and multivariate analysis we generated the metabolite profiles of rice koji produced by fermentation with Aspergillus oryzae (RK_AO) or Bacillus amyloliquefaciens (RK_BA) for different durations. Two principal components of the metabolomic data distinguished the rice koji samples according to their fermenter species and fermentation time. Several enzymes secreted by the fermenter species, including α-amylase, protease, and β-glucosidase, were assayed to identify differences in expression levels. This approach revealed that carbohydrate metabolism, serine-derived amino acids, and fatty acids were associated with rice koji fermentation by A. oryzae, whereas aromatic and branched chain amino acids, flavonoids, and lysophospholipids were more typical in rice koji fermentation by B. amyloliquefaciens. Antioxidant activity was significantly higher for RK_BA than for RK_AO, as were the abundances of flavonoids, including tricin, tricin glycosides, apigenin glycosides, and chrysoeriol glycosides. In summary, we have used MS-based metabolomics and enzyme activity assays to evaluate the effects of using different microbial species and fermentation times on the nutritional profile of rice koji.
Highlights
Fermented food is well-known for its nutritional benefits and biological activities [1]
Through mass spectrometry (MS)-based metabolite profiling, we identified differences between the metabolites in rice koji inoculated with a fungus (A. oryzae) and that inoculated with a bacterial species (Bacillus amyloliquefaciens)
Principal Component 1 (PC1) (46.9%) distinguished the rice koji by fermentation time, and the rice koji samples fermented for 24 h and 36 h were clustered for both the
Summary
Fermented food is well-known for its nutritional benefits and biological activities [1]. Because rice koji is an enzyme source, fermentation with this product affects the quality of the fermented food. Microorganisms produce enzymes involved in metabolite hydrolysis and synthesis, which enhances the flavor, taste, and bioactivities of the fermented foods [5,6]. A nuruk is one of the traditional starter cultures naturally fermented with various airborne microorganisms, whereas koji is fermented by a single microbe under regulated conditions to enhance flavor and enzymatic activity [7]. A. oryzae exhibit strong activity of enzymes such as amylase, protease, and peptidase, and secretes various hydrolytic enzymes [8]. This fungus is Molecules 2016, 21, 773; doi:10.3390/molecules21060773 www.mdpi.com/journal/molecules
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
