Identification of sensory attributes that drive the likeability of Korean rice wines by American panelists. [Corrected].

Six commercial Korean rice wines were described their sensory profiles by trained American panelists, and assessed acceptances by American subjects to identify the drivers of liking and disliking factors. Thirteen statistically different descriptive attributes were defined for Korean rice wines: aromas (apple, pear, earthy, peach, nutty, yeasty, honey), flavor (yeasty, nutty), taste (sweet, sour, bitter), and aftertaste (apricot). Samples A and F were characterized as sweet taste and fruity attributes, and sample C was characterized as being pear flavor and bitter taste. Sample B exhibited a strong earthy aroma, determined as the aroma of ginseng. The American subjects could not identify ginseng aroma due to their lack of experience in ginseng. Samples D and E were described as nutty and yeasty. In consumer test, consumer preference was skewed to sample A, for which the consumer preference revolved around the sweet, sour, and fruity characteristics of the sample by the principal component analysis. Few consumers expressed preference toward samples D and E, as evidenced by the lowest consumer acceptance ratings. Partial least squares regression revealed that the key liking factors of Korean rice wines were sweet, sour, and apricot flavors. Fruity characteristics (peach, apple, and pear) were also positively correlated with overall acceptance. The key disliking factors were yeasty and nutty characteristics. American subjects regarded Korean rice wine as belonging to the wine category, prompting them to grant the highest rank to sample A, which has similar characteristics to semisweet white wine.

Identification of Wild Yeast Strains and Analysis of Their ß-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 ß-glucan and glutathione in various yeast strains isolated from traditional Korean Nuruk and selected a ß-glucan- and glutathione-rich yeast strain to add value to Makgeolli by enhancing its physiological functionality through increased levels of these compounds. Yeast ß-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 µg/mg glutathione, 0.70 µg/mg oxidized glutathione, and 11.69 µg/g and 47.85 µg/g spermidine and L-ornithine monohydrochloride, respectively. To produce functional Makgeolli, a ß-glucan- and glutathione-rich yeast strain was selected in a screening analysis. Makgeolli fermented with the selected yeast strain contained higher ß-glucan and glutathione levels than commercial Makgeolli. Using the selected yeast strain to produce Makgeolli with high ß-glucan and glutathione content may enable the production of functional Makgeolli.

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 µg/mL) and leucine (362.77 µg/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.

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.

Microbial dynamics of commercial makgeolli depending on the storage temperature.

Market fresh makgeolli was stored at different temperatures of 4°C and 25°C to assess the change of the microbial diversity according to the storage temperature and period. Yeast counts increased until day 3 of storage and decreased thereafter. General and lactic acid bacterial counts continuously increased during storage. The data indicated that the control of growth of microorganisms, particularly general bacteria and lactic acid bacteria (LAB), is essential. Total acid levels started to decrease in the makgeolli stored at 4°C, and increased from day 6 of storage in the makgeolli stored at 25°C. The increase of total acid in the non-refrigerated condition greatly affected the quality of makgeolli. In both the fresh makgeolli samples stored at 4°C and 25°C, yeast (Saccharomyces cerevisiae) and molds (Aspergillus tubingensis, Candida glaebosa, and Aspergillus niger) were noted. Denaturing gradient gel electrophoresis (DGGE) band patterns were almost constant regardless of the storage period. As for bacteria, Lactobacillus crustorum, L. brevis, and Microlaena stipoides were found in the makgeolli stored at 4°C, and L. crustorum, Lactobacillus sp., L. plantarum, L. brevis, L. rhamnosus, and L. similis were found in the makgeolli stored at 25°C. In particular, in the makgeolli stored at 25°C, L. crustorum and L. plantarum presented dark bands and were identified as the primary microorganisms that affected spoilage of fresh makgeolli.

Characterization of new antihypertensive angiotensin I-converting enzyme inhibitory peptides from Korean traditional rice wine.

This study describes the characterization of a new angiotensin I-converting enzyme (ACE) inhibitory peptide from a Korean traditional rice wine. After purification of the ACE inhibitor peptides with ultrafiltration, Sephadex G-25 column chromatography, and successively C18 and SCX solid-phase extraction, reverse-phase HPLC, and size exculsion chromatography, two types of the purified ACE inhibitors with IC50 values of 0.34 mg/ml and 1.23 mg/ml were finally obtained. The two purified ACE inhibitors (F-1 and F-2) were found to have two kinds of novel oligopeptides, showing very little similarity to other ACE inhibitory peptide sequences. The amino acid sequences of the two purified oligopeptides were found to be Gln- Phe-Tyr-Ala-Val (F-1) and Ala-Gly-Pro-Val-Leu-Leu (F-2), and their molecular masses were estimated to be 468.7 Da (F-1) and 357.7 Da (F-2), respectively. They all showed a clear antihypertensive effect on spontaneously hypertensive rats at a dosage of 500 mg/kg.

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 25℃ 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.

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

The objective of this study was to find useful fungi with α-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, α-amylase activity, saccharogenic power (SP), starch hydrolysis activity and acid producing activity were evaluated. Ten strains were selected by α-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.

Characterization of yakju brewed from glutinous rice and wild-type yeast strains isolated from nuruks.

Korean traditional rice wines yakju and takju are generally brewed with nuruk as the source of the saccharogenic enzymes by natural fermentation. To improve the quality of Korean rice wine, the microorganisms in the nuruk need to be studied. The objective of this research was to improve the quality of Korean wine with the wild-type yeast strains isolated from the fermentation starter, nuruk. Only strain YA-6 showed high activity in 20% ethanol. Precipitation of Y89-5-3 was similar to that of very flocculent yeast (〉80%) at 75.95%. Using 18S rRNA sequencing, all 10 strains were identified as Saccharomyces cerevisiae. Volatile compounds present in yakju were analyzed by gas chromatography-mass selective detector. The principal component analysis (PCA) of the volatile compounds grouped long-chain esters on the right side of the first principal component, PC1; these compounds were found in yakju that was made with strains YA-6, Y89-5-3, Y89-5- 2, Y90-9, and Y89-1-1. On the other side of PC1 were short-chain esters; these compounds were found in wines that were brewed with strains Y183-2, Y268-3, Y54-3, Y98-4, and Y88-4. Overall, the results indicated that using different wild-type yeast strains in the fermentation process significantly affects the chemical characteristics of the glutinous rice wine.

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 25℃ using S. cerevisiae.