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

Abstract

Production of good Koji 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 Koji samples fermented individually with Bacillus amyloliquefaciens and Aspergillus oryzae. 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 Bacillus-fermented Koji (Bacillus Koji, BK), potentially due to the increased levels of lipid oxidation. A cheesy and rancid flavor was characteristic of Bacillus Koji, 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 Bacillus Koji. Alternatively, malty flavor compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal) and sweet flavor compounds (monosaccharides and maltol) were relatively abundant in Aspergillus-fermented Koji (Aspergillus Koji, AK). Hence, we argue that the VOC profile of Koji is largely determined by the rational choice of inocula, which modifies the primary metabolomes in Koji substrates, potentially shaping its volatolome as well as the aroma characteristics.

Distinctive Formation of Volatile Compounds in Fermented Rice Inoculated by Different Molds, Yeasts, and Lactic Acid Bacteria

“…The fold changes of volatile compounds, which were calculated compared to the control (RICE), were classified by three main metabolic pathways, including carbohydrate, amino acid, and fatty acid metabolism (Table S1). Heatmaps were clustered by defined pathways provided from kyoto encyclopedia of genes and genomes (KEGG) pathways and previous studies [15,16,17]. The tendency to increase or decrease compared to the control was shown in five stages (blue; positive, red; negative, and gray; not detected), while the formation of volatile compounds which were not detected in the control but were newly produced during fermentation, were marked separately (purple; newly detected, white; not detected).…”

“…For example, S. cerevisiae is well known as a higher producer of ethanol and fusel alcohols. In addition, 2-methylbutanal and 3-methylbutanal are major fermentative compounds, induced from fungi, such as A. oryzae [16], while lactic acid bacteria are superior for generating organic acids, including acetic acid, and butanediol fermentation [37]. However, we were able to investigate the characteristic features of volatile compound profiles in rice fermentation according to each microbe.…”

Application of gas chromatography–mass spectrometry (GC‐MS)‐based metabolomics for the study of fermented cereal and legume foods: A review

“…Seo et al . (2018a) and Seo et al . (2018b) studied koji produced from soybean and a combination of cereals.…”

“…Using a combination of SPME‐GC‐MS and GC‐TOF‐MS‐based metabolomics, Seo et al . (2018a) compared the volatile organic compounds and primary metabolites in koji samples fermented individually with Bacillus amyloliquefaciens and Aspergillus oryzae . Through these integrated approaches, the authors concluded that the volatile profile of koji is largely determined by the inocula choice, which modifies the primary metabolites in koji substrates, subsequently influencing its aroma characteristics.…”

Comparison of volatile profiles in Fagopyrum esculentum (buckwheat) soksungjang prepared with different starter cultures during fermentation

“…Numerous studies focused on Bacillus and Aspergillus species as the main microorganisms in fermented soybean products and found volatile organic acids, alcohols, and esters were predominant and their levels varied with the associated microorganisms during fermentation process (Kum et al, 2015;Leejeerajumnean et al, 2001;Seo et al, 2018). Recently, Seo et al (2018) reported the differences of volatile profiles between koji fermented by B. amyloliquefaciens and A. oryzae.…”