Microbial Diversity and Volatile Flavor Changes during Gayangju Fermentation, a Traditional Korean House Rice Wine

Abstract

Physicochemical changes in fermented alcoholic beverages are significantly related to microbial community development during fermentation. Due to its unusually long fermentation, Gayangju, a traditional Korean house rice wine fermented with nuruk as the traditional starter, gives rise to a strong yeast community and, therefore, a high ethanol concentration and different flavors. However, no detailed analysis has been examined. Changes in microbial community structure during Gayangju fermentation were examined using both culture-dependent and culture-independent methods. During fermentation, Saccharomyces cerevisiae and Saccharomycopsis fibuligera were dominant during all stages of the fermentation. In contrast, Candida parapsilosis, Hanseniaspora guilliermondii, Pichia anomala, Malassezia cuniculi and P. fermentans were identified as minor. P. anomala appeared after the second brewing and then remained constant. Among the 19 compounds identified in this study as order-active compounds, 2-methyl-1-butanol (isoamyl alcohol) was the major compound that increased during the long fermentation stage. Most of the odor-active compounds such as 2,3-butanediol, 3-methyl-1-butanol, ethyl tetradecanoate, ethyl decanoate, ethyl dodecanoate, butanoic acid, 3-methylbutanoic acid (isovaleric acid), 2-methylbutanoic acid, 2-methyl-1-propanol, ethyl acetate, ethyl caprylate, 2-phenylethanol, and 3-methylbutyl acetate increased as the fermentation progressed during 68 days of fermentation, which showed significant differences in the concentrations of odor-active compounds of commercially fermented makgeolli.

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“…Moreover, a pH range between 3 and 4 units contributes to creating a favorable environment for yeast activity and, at the same time, protects the wine from growth of other microorganisms (Arranz, 2006). The pH oscillated between 3.10and 3.61 (grape wines, G), between 3.35 and 3.86 (TF wines), and between 3.30 and 3.70 (rice wines, R), optimal values to maintain the stability and prevent oxidation and browning reactions of the wine, and similar to those reported by different authors (Gavimath et al, 2012;Koay et al, 2022;Páramo & Peck, 2006;Plavsa et al, 2012;Song et al, 2022). The total acidity was significatively higher in G4 wine (20 meq L −1 , p < 0.05), while in the remaining wines the values ranged from 9.45 (TF3) to 17 meq L −1 (G2).…”