This study presents a cost-effective strategy for producing organic acids from glucose and xylose using the acid-tolerant yeast, Issatchenkia orientalis. I. orientalis was engineered to produce lactic acid from xylose, and the resulting strain, SD108XL, successfully converted sorghum hydrolysates into lactic acid. In order to enable low-pH fermentation, a self-buffering strategy, where the lactic acid generated by the SD108XL strain during fermentation served as a buffer, was developed. As a result, the SD108 strain produced 67 g/L of lactic acid from 73 g/L of glucose and 40 g/L of xylose, simulating a sugar composition of sorghum biomass hydrolysates. Moreover, techno-economic analysis underscored the efficiency of the self-buffering strategy in streamlining the downstream process, thereby reducing production costs. These results demonstrate the potential of I. orientalis as a platform strain for the cost-effective production of organic acids from cellulosic hydrolysates.

Nuruk is a traditional Korean fermentation starter containing various microbes; it is utilized for the synthesis of alcoholic beverage. In this study, the changes in the quality characteristics and microbial community during the cultivation period of nuruk were analyzed. The results indicated that the fungal richness, expressed as Chao 1, from 70.0 to 19.3 on day 10 and subsequently increased to 35.0 on day 30 of cultivation. The content ratio of Aspergillus sp., Rhizopus sp. and Saccharomycopsis sp. increased with the progress of cultivation. Among the fungi, the content of the Aspergillus genus increased from 0.01% before cultivation to 70.4 %. Among the bacteria, the content of the Pantoea genus increased to 69.76% on day 7 and decreased to 44.80% on day 14. Considering the enzyme activity, saccharogenic power, α-amylase and carboxy peptidase exhibited the highest activity on day 7 while lipase exhibited the highest activity on day 14. Considering only the enzyme activity, the results indicated that it would be appropriate to terminate cultivation before day 14. The traditional cultivation period of nuruk is approximately 14 days; However, it is necessary to determine a suitable cultivation period for the application of nuruk as enzyme source.

This study aimed to control sugar consumption during makgeolli fermnetation using high temperature treatments after 3 days of fermentation at normal temprature. makgeolli fermentation was performed at 25°C for the initial 3 days and at 34, 37, 40, and 43°C, respectively, for the next 4 days. When fermented at 25°C (control), the alcohol content increased up to 16.5%; however the alcohol content of makgeolli treated at elevated temperatures reduced by 13.8 %. In the control group, typical saccharification and fermentation proceeded simultaneously, and the reducing sugar content remained low due to sugar consumption by active yeast. However, at high fermentation temperatures, the nuruk enzymes functioned normally and saccharification proceeded well; however the conversion of fermentable sugars to alcohol was inhibited, possibly due to a decrease in yeasts activity. The viable cell count of yeasts was 4-6 log CFU/mL regardless of the fermentation temperature. These results indicate the possibility of producing sweet live-yeast makgeolli without the addition of artificial sweeteners through a temperature-controlled makgeolli fermentation.

The soju (Korean traditional distilled liquor) market is increasing worldwide. However, in contrast to well-explored distilled liquors, including baijiu (China) and shochu (Japan), soju is less investigated, with limited research on its aroma characteristics. To facilitate better understanding of the aroma characteristics of soju, this study aims to overview recent research on the flavor characteristics of soju and compare data with those of baijiu and shochu, well-established products in the market. Soju is generally made using rice and nuruk (a traditional Korean fermentation starter). Previous studies have reflected that the aroma characteristics vary with raw materials’ nutrition percentages, microbial taxa influenced in fermentation starters, and/or pressure reduction during distillation. The research on the aroma characteristics of baijiu, characterized by solid-state fermentation involving qu (a traditional Chinese fermentation starter), is focused on differences in regional characteristics of the flavor type. Research on the aroma characteristics of shochu has primarily demonstrated that the microbial community could contribute significantly to the development of specific aromatic compounds and/or attributes. Moreover, the association of the aroma characteristics of baijiu and shochu with their volatile compound development by the determination of selective ingredients has been examined. Understanding the current research progress can potentially facilitate the improvement in the aroma characteristics of soju.

This study aimed to identify the key volatile compounds and their contributions to the sensory characteristics of commercial makgeolli. Quantitative descriptive analysis of six makgeolli samples revealed ten sensory attributes (eight aroma and two taste attributes), with significant differences among samples. Notably, samples using different traditional nuruk showed distinct characteristics: some exhibited strong fermented and acidic notes, while others demonstrated predominant fruit notes, highlighting the crucial role of nuruk quality in determining sensory properties. Gas chromatography-mass spectrometry (GC-MS) analysis identified 43 volatile compounds, with 13 compounds commonly present across samples. Gas chromatography-olfactometry (GC-O) analysis revealed 38 aroma-active compounds, among which isoamyl alcohol, ethyl caprate, methionol, and 2-phenylethanol were identified as fundamental aroma compounds through both GC-O and odor activity values (OAVs) analyses. Correlation analysis demonstrated significant relationships between volatile compounds and sensory characteristics: isoamyl alcohol strongly correlated with alcohol and banana-like notes (r>0.90), while methional showed strong association with nuruk-like aroma (r=0.908). Notably, phenylethanol exhibited high values in instrumental analyses and was characterized by rose notes in GC-O; however, these characteristics were not distinctly perceived in sensory evaluation, suggesting masking effects in the complex matrix. This comprehensive analytical approach provides insights into the relationship between volatile compounds and sensory characteristics of makgeolli, emphasizing the importance of systematic quality evaluation in makgeolli.