Metabolite Profiling during Fermentation of Makgeolli by the Wild Yeast Strain Saccharomyces cerevisiae Y98-5

Makgeolli is a traditional Korean alcoholic beverage. The flavor of makgeolli is primarily determined by metabolic products such as free sugars, amino acids, organic acids, and aromatic compounds, which are produced during the fermentation of raw materials by molds and yeasts present in nuruk, a Korean fermentation starter. In this study, makgeolli was brewed using the wild yeast strain Saccharomyces cerevisiae Y98-5, and temporal changes in the metabolites during fermentation were analyzed by ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry. The resultant data were analyzed by partial least squares-discriminant analysis (PLS-DA). Various metabolites, including amino acids, organic acids, sugar alcohols, small peptides, and nucleosides, were obviously altered by increasing the fermentation period. Changes in these metabolites allowed us to distinguish among makgeolli samples with different fermentation periods (1, 2, 3, 6, 7, and 8 days) on a PLS-DA score plot. In the makgeolli brewed in this study, the amounts of tyrosine (463.13 microg/mL) and leucine (362.77 microg/mL) were high. Therefore, our results indicate that monitoring the changes in metabolites during makgeolli fermentation might be important for brewing makgeolli with good nutritional quality.

Identification of Wild Yeast Strains and Analysis of Their beta-Glucan and Glutathione Levels for Use in Makgeolli Brewing

Makgeolli, also known as Takju, is a non-filtered traditional Korean alcoholic beverage that contains various floating matter, including yeast cells, which contributes to its high physiological functionality. In the present study, we assessed the levels of beta-glucan and glutathione in various yeast strains isolated from traditional Korean Nuruk and selected a beta-glucan- and glutathione-rich yeast strain to add value to Makgeolli by enhancing its physiological functionality through increased levels of these compounds. Yeast beta-glucan levels ranged from 6.26% to 32.69% (dry basis) and were strongly species-dependent. Dried Saccharomyces cerevisiae isolated from Nuruk contained 25.53 microg/mg glutathione, 0.70 microg/mg oxidized glutathione, and 11.69 microg/g and 47.85 microg/g spermidine and L-ornithine monohydrochloride, respectively. To produce functional Makgeolli, a beta-glucan- and glutathione-rich yeast strain was selected in a screening analysis. Makgeolli fermented with the selected yeast strain contained higher beta-glucan and glutathione levels than commercial Makgeolli. Using the selected yeast strain to produce Makgeolli with high beta-glucan and glutathione content may enable the production of functional Makgeolli.

Microbiological Characteristics of Wild Yeast Strain Pichia anomala Y197-13 for Brewing Makgeolli

Makgeolli is a traditional cloudy-white Korean rice wine with an alcohol content of 6~7%. The present study investigated the morphological characteristics, carbon-utilizing ability, fatty acid composition, alcohol resistance, glucose tolerance, and flocculence of Saccharomyces cerevisiae Y98-5 and Pichia anomala Y197-13, non-S. cerevisiae isolated from Nuruk, which is used in brewing Makgeolli. Similar morphological characteristics were observed for both isolated wild yeast strains; and the carbon source assimilation of Y197-13 differed from that of other P. anomala strains. Strain Y197-13 was negative for D-trehalose, mannitol, arbutin, I-erythritol, and succinic acid. The major cellular fatty acids of strain Y197-13 included C18:2n6c (33.94%), C18:1n9c (26.97%) and C16:0 (20.57%). Strain Y197-13 was Crabtree-negative, with 60% cell viability at 12% (v/v) ethanol. The flocculation level of strain Y197-13 was 8.38%, resulting in its classification as a non-flocculent yeast.

Identification and Characterization of Useful Fungi with alpha-Amylase Activity from the Korean Traditional Nuruk

The objective of this study was to find useful fungi with alpha-amylase activity from the Korean traditional nuruk for the quality of traditional Korean alcoholic beverage. In this study, 165 samples of traditional nuruk were collected from 170 regions throughout Korea and the fungi were isolated to a total of 384 strains. In order to investigate the effect of microflora on nuruk, alpha-amylase activity, saccharogenic power (SP), starch hydrolysis activity and acid producing activity were evaluated. Ten strains were selected by alpha-amylase activity, which ranged from 458.47 to 1,202.75 U/g. The size of the discolored zone for the starch hydrolysis activity of each fungus ranged from 0.3 to 2 cm. The SP of the 10 strains ranged from 228.8 to 433.4 SP. Of the 10 stains, three were identified as Aspergillus oryzae, two as Aspergillus flavus, two as Lichtheimia sp., one as Rhizopus oryzae and two as other strains. The total aflatoxins present in the nuruks were examined using enzyme-linked immunosorbent assay. The 10 nuruks had less than 1.11 ppb of aflatoxins.

Physiological Functionalities of Vitis hybrid (Sheridan)-Rubus coreanus Red Wine Made by Saccharomyces cerevisiae

Vitis hybrid (Sheridan)-Robus coreanus red wine was vinified by fermentation of a mixture of Vitis hybrid and Robus coreanus must at 25degrees C for 10 days. The Vitis hybrid-Robus coreanus red wine had ethanol contents of 10.9%. It had high antihypertensive angiotensin I-converting enzyme (ACE) inhibitory activity of 57.8% and antioxidant activity of 64.8%. Changes in the physicochemical properties and functionality of the Vitis hybrid-Robus coreanus red wine was investigated during a post-fermentation period of three months. The ACE inhibitory activity of the red wine increased as the post-fermentation period prolonged, and showed the highest ACE inhibitory activity of 70.4% 60 days post-fermentation. However, the antioxidant activity declined significantly to 47.2% during the post-fermentation period of 60 days. In terms of sensory evaluation, the Vitis hybrid-Robus coreanus red wine had the best acceptability 60 days post-fermentation.

Screening of Functional Rhizopus stolonifer for Alcohol Fermentation and Production of High Quality Korean Traditional Rice Wine

Different strains of mold were screened for the production of high quality Korean traditional rice wine with anti-hypertension and good acceptability. We isolated 867 nuruk mold strains and selected 24 for further study based on measurement of amylase activity. Among them, mold No. 17 showed high ethanol production upon fermentation with Saccharomyces cerevisiae as well as anti-hypertensive properties. The No. 17 strain was therefore selected as the functional mold and later identified as Rhizopus stolonifer based on molecular biological characteristics. Optimal fermentation conditions for the brewing of anti-hypertensive traditional rice wine comprised the addition of R. stolonifer No. 17 koji at a concentration of 35 sp/g and a fermentation period of 10 days at 25degrees C using S. cerevisiae.