Abstract ▼

Many Korean alcoholic beverages are made by Nuruk, a traditional Korean fermentation agent, which enables the hydrolysis of the raw materials, which is known to produce richly flavored components in addition to alcohol, giving the final product a pleasant taste.[1, 2]
During the fermentation proc

Many Korean alcoholic beverages are made by Nuruk, a traditional Korean fermentation agent, which enables the hydrolysis of the raw materials, which is known to produce richly flavored components in addition to alcohol, giving the final product a pleasant taste.[1, 2]
During the fermentation process, the yeast cells create a number of spectrums of volatile molecules, such as esters, organic acid, aldehydes, higher alcohols and carbonyl compounds offering sensory characteristics for the beverages[3].
Higher alcohols and esters are noted for their superior concentrations with regard to other secondary metabolites and aroma contributions[4].
In addition to some other elements, the representative components of flavor in traditional Korean alcoholic beverages are ethyl carproate, producing an apple like flavor, isoamyl alcohol, exhibiting a banana like flavor and 2-phenyl alcohol, which provides for a rose like essence; all compounds which normally originate from alcohol fermentation yeasts[5, 6].
One of the acyl esters, ethyl caproate is synthesised by the substrates being ethanol and caproic acid or caproyl-CoA[7].
That is to say that ethyl caproate is produced by condensation of CoA-activated middle-chail-fatty acids with ethanol[8].
The synthesis is inhibited by cerulenin and it is anticipated that the cerulenin-resistant wild yeasts would be stronger producers of caproic acid and ethyl caproate[7].
In traditional Nuruks, there are various wild yeasts which give their rich aroma to traditional Korean alcohols[9].
This study was aimed to screen for highly productive aromatic compound yeasts with high level of concentration of ethyl caproate(primarily), isoamyl alcohol and 2-phenylalcohol, amongst others.
Finding out the potential of the isolated yeasts for use in brewing of Yakju, a variety of traditional Korean alcoholic beverage, was also an important objecive.
Thus, in this study, it was embarked on the isolation of sixty-six wild yeasts from traditional Korean Nuruks.
Then the isolates were screened to eighteen strongly cerulenin-resistants. As the second step, the cerulenin-resistants were subjected to an olfactory evaluation to eliminate those odor.
Then, eight isolates were selected by the olfactory evaluation.
The isolates were three of Wickerhamomyces anolaus(AY1, AY4, AY41), two of Cyberlindnera fabianii(AY46, AY47), one of Saccharomycopsis fibuligera(AY56), Pichia farinosa(AY5) and Geotrichum candidum(AY 6).
These isolates are considered to be at a biosafety level 1(BSL-1), and therefore safe for consumption by humans[10, 12-14].
W. anomalus, Pichia farinosa and Geotrichum candidum produce 2-phenylethanol [14] and are used to remove unpleasant odors in poultry farm environments by way of the feeding of the yeast mixtureto the birds[15].
S. fibuligera also uses sugars and produces alcohols[16].
C. fabianii is know to be strong phytase producers and so can be utilized in water purification facilities and products[17].
Futhermore, C. fabianii was seen to produce a large amount of ethyl caproate in this study. In a research with the traditional Japanese drink, Sake, the highest ethyl caproate producing cerulenin-risistant mutant of Saccharomyces cerevisiae produced five times higher than it's the parental strain[7].
In this study, the ethyl caproate of C. fabianii AY47 in the traditional Korean beverage of Yakju produced a startling 176.6±17.4 ppm and AY1, AY4, AY6, AY41, AY46 and AY56 also produced high concentrations of ethyl caproate (55.0±5.8 to 170.1±11.6).
They have the potential for use to create furity alcoholic beverages.
Therefore, it is expected that the quality of traditional Korean alcoholic beverages to be notably improved by applying these non-Saccharomyces yeasts to fermentation processes.