• The Korean Journal of Mycology
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• v.42 no.3
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• pp.191-200
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• 2014

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 $1,278.9{\pm}21.6$ (${\times}10^4$), $1,868.0{\pm}27.7$ (${\times}10^4$), and $775.1{\pm}19.2$ (${\times}10^4$) 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 ${\beta}$-glucan in crop component of Nuruk since R. oryzae was the only fungus that showed ${\beta}$-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.

• Microbiology and Biotechnology Letters
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• v.43 no.1
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• pp.56-64
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• 2015

It has been known for some time to the wine industry that non-Saccharomyces yeasts play an important role in increasing volatile components through the secretion of extracellular enzymes. The objective of this study was to investigate what types of enzymes are produced by 1,007 non-Saccharomyces yeast strains isolated from Korean fermented foods. Among 1,007 yeast strains, the 566, 45 and 401 strains displayed β-glucosidase, glucanase and protease activity, respectively. In addition, the 563 and 610 strains possessed tolerances against cerulenin and TFL, and the 307 strain was tolerant to 15% ethanol. Yeasts producing harmful biogenic amines and hydrogen sulfide were excluded from further study, and eventually 12 yeast strains belonging to the genera Wickerhamomyces, Hanseniaspora, Pichia, Saccharomyces were identified, based on the 26S rRNA gene sequences. Among the 12 strains, the 9 and 5 strains possessed glucose and ethanol tolerance, respectively. Yeasts belonging to the genus Saccharomyces produced more than 8% alcohol, but non-Saccharomyces yeasts produced only 3% alcohol.

• Food Science and Preservation
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• v.24 no.7
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• pp.1043-1051
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• 2017

Wild yeasts were isolated from domestic non-sterilized Makgeolli and their fermentation characteristics were analyzed to select the best fermentation seed culture. A total of 65 yeast strains isolated yeasts from non-sterilized Makgeolli and Nuruk. In order to select fermentable strains, hydrogen sulfide, $CO_2$ production ability, alcohol tolerance and aroma component production ability were analyzed. To screen the aromatic strains of isolates, media containing cerulenin, 5,5,5-trifluor-DL-leucine (TFL) and API ZYM kit were used. There were 36 strains resistance to cerulenin and all strains produced esterase and demonstrated tolerance against TFL. Hydrogen sulfide, which could degrade the quality of the fermented beverage, was not produced in 34 yeast. The correlation between alcohol tolerance of yeast and carbon dioxide production was analyzed by principal component analysis. YM22, YM31, YM32 and YM37 produced a total of 0.14-0.18 g/72 h of $CO_2$ indicating high fermentability. Alcohol tolerance was measured by alcohol concentration. YM32, YM37 yeast had 20% alcohol tolerance. As a result, alcohol and flavor characteristics of wild yeast isolated from non-sterilized Makgeolli were analyzed and it was confirmed that yeast was suitable for the production of alcohol.

• Korean Journal of Food Science and Technology
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• v.49 no.6
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• pp.605-609
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• 2017

The effect of malic acid-degrading yeast on the quality of Gaeryangmerou (Vitis spp.) wine obtained from grapes commonly used for making wine in Korea was investigated. Alcoholic fermentation was carried out at $25^{\circ}C$, for 14 days. A malic acid-degrading yeast was used as the experimental sample and a commercial yeast, Fermivin, was used as a control. The fermentation process for the experimental yeast lasted 2-3 days longer than that of Fermivin. The pH and the volatile acid content of the wine were 3.94 and 244.20 mg/L, respectively. The total acid content was 0.86% for the experimental group and 0.94% for the control group. The contents of malic acid and succinic acid in the experimental group were significantly lower than that of the control group (245.61, 50.18 mg% for experimental group versus 302.44, 68.39 mg% for control group, respectively). In contrast, lactic acid content was slightly higher in the experimental group. As expected, the main volatile flavor compounds of Gaeryangmerou wine varied with the yeast used for fermentation and were determined to be isoamyl alcohol, ${\beta}$-phenethyl alcohol, 2-methyl-1-propanol, and diacetyl for the experimental wine.