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International Journal of Food Microbiology
Vol. 232, 2016, Pages: 1521


New insight into microbial diversity and functions in traditional Vietnamese alcoholic fermentation

Vu Nguyen Thanh, Nguyen Thanh Thuy, Nguyen Thuy Chi, Dinh Duc Hien, Bui Thi Viet Ha, Dao Thi Luong, Pham Duc Ngoc, Pham Van Tyb

Food Industries Research Institute, 301 Nguyen Trai, Thanh Xuan, Hanoi, Viet Nam.

Abstract

The roles of microorganisms in traditional alcoholic fermentation are often assumed based on abundance in the starter and activity in pure culture. There is a serious lack of hard evidence on the behavior and activity of individual microbial species during the actual fermentation process. In this study, microbial succession and metabolite changes during 7 days of traditional Vietnamese alcoholic fermentation were monitored. Special attention was devoted to starch degradation. In total, 22 microbial species, including 6 species of filamentous fungi (Rhizopus microsporusRhizopus arrhizusMucor indicusMucor circinelloidesCunninghamella elegansAspergillus niger), 1 yeast-like fungus (Saccharomycopsis fibuligera), 7 yeasts (Saccharomyces cerevisiaeClavispora lusitaniaeWickerhamomyces anomalusLindnera fabianiiPichia kudriavzeviiCandida rugosaCandida tropicalis), and 8 bacteria (Stenotrophomonas maltophiliaLactobacillus brevisLactobacillus helveticusAcinetobacter baumanniiStaphylococcus hominisBacillus megateriumEnterobacter asburiaePediococcus pentosaceus) were identified. Despite the presence of a complex microbiota in the starter, the fermentation process is consistent and involves a limited number of functional species. Rapid change in microbial composition of fermentation mash was observed and it was correlated with ethanol content. Microbial biomass reached maximum during first 2 days of solid state fermentation. Acidification of the medium took place in day 1, starch degradation in days 2, 3, 4, and alcohol accumulation from day 3. Although Sm. fibuligera dominated by cell count amongst potential starch degraders, zymography indicated that it did not produce amylase in the fermentation mash. In mixed culture with Rhizopus, amylase production by Sm. fibuligera is regulated by the moisture content of the substrate. Rhizopus was identified as the main starch degrader and S. cerevisiae as the main ethanol producer. Bacterial load was high but unstable in species composition and dominated by acid producers. M. indicusSm. fibuligeraW. anomalus and bacteria were regarded as satellite microorganisms. Their possible influence on organoleptic quality of fermentation product was discussed.

Keywords: Traditional alcoholic fermentation; Amylolytic starter; Microbial succession; Rhizopus; Saccharomycopsis fibuligera; Amylase.

 
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