Diversity, Saccharification Capacity, and Toxigenicity Analyses of Fungal Isolates in Nuruk

Abstract

: Nuruk samples collected from various regions in Korea were investigated in terms of fungal contents and diversity. In measurement of colony forming unit (CFU) in Nuruk suspensions on DRBC agar, Nuruk samples MS4, MS8, and MS10 were among the highest fungal density, with 1,278.9±21.6 (×10 ) were among the samples showing the highest fungal density. CFU per 20 mg Nuruk, respectively. The majority of fungal components were yeasts, including Pichia anomala, P. kudriavzevii, Kluyveromyces marxianus, and Saccharomycopsis fibuligera, whereas Aspergillus oryzae and Rhizopus oryzae, the representative Nuruk fungi, were predominant only in the low fungal density Nuruks (MS2, MS5, and MS11). Saccharification capability of the fungal isolates was assessed by measurement of amylase activity in the culture broth. The highest amylase activity was found in A. niger and A. luchuensis, followed by S. fibuligera. A. oryzae and R. oryzae showed fair amylase activity but significantly lower than those of the three fungal species. R. oryzae was suggested to play an additional role in degradation of β-glucan in crop component of Nuruk since R. oryzae was the only fungus that showed β-glucanase activity among the fungal isolates. To confirm the safety of Nuruk, aflatoxigenicity of the isolated Aspergillus was estimated using the DNA markers norB-cypA, aflR, and omtA. All of the isolates turned out to be non-aflatoxigenic as evidenced by the deletion of gene markers, norB-cypA and aflR, and the absence of aflatoxin in the culture supernatants shown by TLC analysis.

Influence of aflatoxin in Nuruk on the safety of starch‐based alcoholic beverage

“…Kim et al. () determined that A. flavus and A. parasiticus strains isolated from traditional Nuruk were atoxigenic by observing deletions in the AF gene cluster, such as those in afl R, omt A, and norb‐cyp A genes, and by identifying an AF band through TLC analysis.…”

Concept of Nuruk on Brewing Technology

“…Specifically, various types of yeast, lactic acid bacteria, and aerobic bacteria that cause alcoholic fermentation are present in Nuruk. Some kinds of Nuruk derived microorganisms that were found by Kim et al [14] are shown in Figure 5.…”

“…Therefore, fermentative molds in low pH environment exhibit high liquefaction and glycation Figure 5. The filamentous fungi and yeasts isolated from various Nuruk samples (scale bar = 5 μm) [14].…”

“…In Korea, research on traditional Nuruk was started in the early 1900s by the Japanese, but had not actively progressed until recently. Currently, research on the production of certain traditional Nuruk [2][3][4], Nuruk-derived microorganisms [5][6][7][8][9], traditional Nuruk-derived Korean alcoholic beverages [10][11][12][13], and their physiological functions [14][15][16][17] are being performed. In addition, investigation on the Nuruk microbial communities [18][19][20] as well as the metabolite analysis of Nuruk [20] was recently performed.…”

Makgeolli - The Traditional Choice of Korean Fermented Beverage from Cereal: An Overview on its Composition and Health Benefits

“…It was found that the strains of Rhizopus oryzae produce carbohydratedigesting enzymes along with organic acids, ethanol and some useful esters, which can be useful in food industries. Aspergillus fumigatus and Paecilomyces variotii is a fast growing microfungi (that can grow efficiently under a variety of environmental conditions), which shows beneficial effects on human health as an emerging agent of opportunistic disease, particularly to boost the immune system (Kim et al, 2014b;Jang et al, 2014). Recently, Kim et al (2019).…”