Evaluating the Headspace Volatolome, Primary Metabolites, and Aroma Characteristics of Koji Fermented with Bacillus amyloliquefaciens and Aspergillus oryzae

Abstract

Production of good <i>Koji</i> primarily depends upon the selection of substrate materials and fermentative microflora, which together influence the characteristic flavor and aroma. Herein, we performed comparative metabolomic analyses of volatile organic compounds (VOCs) and primary metabolites for <i>Koji</i> samples fermented individually with <i>Bacillus amyloliquefaciens</i> and <i>Aspergillus oryzae</i>. The VOCs and primary metabolites were analyzed using headspace solid phase microextraction (HS-SPME) followed by gas chromatography time-of-flight mass spectrometry (GC-TOF-MS). In particular, alcohols, ketones, and furans were mainly detected in <i>Bacillus</i>-fermented <i>Koji</i> (<i>Bacillus Koji</i>, BK), potentially due to the increased levels of lipid oxidation. A cheesy and rancid flavor was characteristic of <i>Bacillus Koji</i>, which is attributable to high content of typical 'off-flavor' compounds. Furthermore, the umami taste engendered by 2-methoxyphenol, (E,E)-2,4-decadienal, and glutamic acid was primarily detected in <i>Bacillus Koji</i>. Alternatively, malty flavor compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal) and sweet flavor compounds (monosaccharides and maltol) were relatively abundant in <i>Aspergillus</i>-fermented <i>Koji</i> (<i>Aspergillus Koji</i>, AK). Hence, we argue that the VOC profile of <i>Koji</i> is largely determined by the rational choice of inocula, which modifies the primary metabolomes in <i>Koji</i> substrates, potentially shaping its volatolome as well as the aroma characteristics.