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( Jyotiranjan Bal ),( Suk-hyun Yun ),( Jeesun Chun ),( Beom-tae Kim ),( Dae-hyuk Kim ) 한국균학회 2016 Mycobiology Vol.44 No.3
The most economically important species used in a wide range of fermentation industries throughout Asia belong to Aspergillus section Flavi, which are morphologically and phylogenetically indistinguishable, with a few being toxigenic and therefore a major concern. They are frequently isolated from Korean fermentation starters, such as nuruk and meju. The growing popularity of traditional Korean alcoholic beverages has led to a demand for their quality enhancement, therefore requiring selection of efficient non-toxigenic strains to assist effective fermentation. This study was performed to classify the most efficient strains of Aspergillus section Flavi isolated from various types of traditional wheat nuruk, based on a polyphasic approach involving molecular and biochemical evaluation. A total of 69 strains were isolated based on colony morphology and identified as Aspergillus oryzae/flavus based on internal transcribed spacer and calmodulin gene sequencing. Interestingly, none were toxigenic based on PCR amplification of intergenic regions of the aflatoxin cluster genes norB-cypA and the absence of aflatoxin in the culture supernatants by thin-layer chromatography analysis. Saccharification capability of the isolates, assessed through α-amylase and glucoamylase activities, revealed that two isolates, TNA24 and TNA15, showed the highest levels of activity. Although the degrees of variation in α-amylase and glucoamylase activities among the isolates were higher, there were only slight differences in acid protease activity among the isolates with two, TNA28 and TNA36, showing the highest activities. Furthermore, statistical analyses showed that α-amylase activity was positively correlated with glucoamylase activity (p < 0.001), and therefore screening for either was sufficient to predict the saccharifying capacity of the Aspergillus strain.
Pyrosequencing reveals bacterial diversity in Korean traditional wheat-based nuruk
Jyotiranjan Bal,윤석현,최명석,여수환,김정미,김대혁 한국미생물학회 2015 The journal of microbiology Vol.53 No.12
The emerging global importance of Korea’s alcoholic beverages emphasizes the need for quality enhancement of nuruk, a traditional Korean cereal starter that is used extensively in traditional brewing. Apart from fungi and yeasts, bacteria known to be ubiquitously present are also a part of the nuruk ecosystem and are known to influence fermentation activity by influencing fermentation favorable factors. In the current study, bacterial diversity and temporal variations in the traditional wheat-based nuruk, fermented at two representative temperature conditions for 30 days, along with two commercial wheat-based nuruk samples for comparison analysis were evaluated using libraries of PCR amplicons and 454 pyrosequencing targeting of the hypervariable regions V1 to V3 of the 16S rRNA gene. A total of 90,836 16S reads were analyzed and assigned to a total of 314, 321, and 141 Operational Taxonomic Units (OTUs) for nuruk A, B, and C, respectively. Diversity parameters clearly indicated nuruk B to be more diverse in terms of bacterial composition than nuruk A. Taxonomic assignments indicated that nuruk A was dominated by phylum Cyanobacteria, whereas nuruk B was dominated by phylum Actinobacteria. For both nuruk A and B, members of the phylum Firmicutes mostly converged into the family Bacillaceae; these microorganisms might be present in negligible numbers at the beginning but became significant as the fermentation progressed. The commercial samples were predominated by phylum Firmicutes, which is composed of Lactobacillaceae and Leoconostocaceae. The findings of this study provide new insights into understanding the changes in bacterial community structure during traditional nuruk starter production.
Mycoflora Dynamics Analysis of Korean Traditional Wheat-based Nuruk
Jyotiranjan Bal,윤숙현,송하연,여수환,김재현,김정미,김대혁 한국미생물학회 2014 The journal of microbiology Vol.52 No.12
The growing popularity of traditional Korean alcoholic beverageshas led to a demand for quality enhancement of thetraditional starter culture nuruk, which consists primarilyof wheat. Therefore, this study focused on mycoflora characterizationand the temporal variations in traditional wheatbasednuruks fermented at two representative traditional temperatureconditions for 30 days. Nuruk A was fermented at aconstant temperature of 36°C for 30 days and nuruk B wasfermented at a high initial temperature of 45°C for 10 daysfollowed by 35°C for 20 days. The average mycoflora load inthe two different nuruk conditions did not vary significantlybetween the 0 and 30 day cultures, and a maximum load of8.39 log CFU/g was observed for nuruk A on culture day 3and 7.87 log CFU/g for nuruk B on culture day 30. Within twosamples, pH was negatively correlated with temporal changesin mycoflora load. The pH of nuruk A was significantly lowerthan that of nuruk B at all of the time points evaluated. Culture-dependent characterization led to the identification of55 fungal isolates belonging to 9 genera and 15 species, withthe most prominent genera comprising Lichtheimia, Penicillium,Trametes, Aspergillus, Rhizomucor, and Mucor. A totalof 25 yeast isolates were characterized belonging to 6 generaand 7 species, the most prominent among which were Rhodotorula,Pichia, Debaryomyces, Saccharomycopsis, and Torulospora. Mycofloral community dynamics analysis revealedthat both samples A and B varied considerably with respectto the fungal communities over a span of 30 days.
Bal, Jyotiranjan,Yun, Suk-Hyun,Yeo, Soo-Hwan,Kim, Jung-Mi,Kim, Beom-Tae,Kim, Dae-Hyuk Springer-Verlag 2017 Applied microbiology and biotechnology Vol.101 No.5
<P>The brewing of makgeolli, one of Korea's most popular alcoholic beverages that is gaining popularity globally, is facilitated by nuruk, a traditional Korean cereal starter. The nuruk microbiome greatly influences the fermentation process as well as the nutritional, hygienic, and aromatic qualities of the product. This study is a continuation of our efforts to examine nuruk biodiversity at a depth previously unattainable. In this study, microfloral dynamics in wheat-based nuruk C, composed of traditional ingredients such as barley, green gram, and wheat and fermented under various internal moisture contents of 20% (C20), 26% (C26), and 30% (C30), was evaluated using 454 pyrosequencing during the 30-day fermentation process. Rarefaction analysis and alpha diversity parameters indicated adequate sampling. C20 showed the greatest fungal richness and diversity, C20 and C26 exhibited similar bacterial richness and diversity, while C30 had low fungal and bacterial richness. Fungal taxonomic assignments revealed that the initial moisture content caused selective enrichment of Aspergillus candidus with a decreasing trend during fermentation, whereas Saccharomycetales sp. exhibited increasing relative abundance with increasing moisture content from day 6 of the fermentation process. Depending on initial moisture level, changes in bacterial communities were also observed in the genera Streptomyces, Bacillus, and Staphylococcus, with decreasing trends whereas Saccharopolyspora exhibited a sigmoidal trend with the highest abundance in C26. These findings demonstrate the possible impact of initial moisture content of nuruk on microfloral richness, diversity, and dynamics; this study is thus a step toward our ultimate goal of enhancing the quality of nuruk.</P>