Moeun Lee, Daun Kim, and Ji Yoon Chang. J. Microbiol. Biotechnol. 2024;34:306-13. https://doi.org/10.4014/jmb.2308.08015

This study was conducted to confirm the effectiveness of kimchi starters (KSs) by investigating their growth characteristics. First, we assessed the growth characteristics of five lactic acid bacteria (LAB) strains (Lactococcus lactis WiKim0124; Companilactobacillus allii WiKim39; and Leuconostoc mesenteroides WiKim0121, WiKim33, and WiKim32) and assessed the effects of different parameters, including organic acids, salinity, acidity, and temperature, on the growth of these LAB. The findings showed that organic acids, particularly acetic and lactic acids that accumulated with the progress in fermentation, were the major players determining the microbial composition of kimchi and the growth of the KSs. Leuconostoc mesenteroides grew well in the presence of acetic and lactic acids than other starts, so it is confirmed that Leuconostoc mesenteroides can dominant in kimchi. In addition, malic acid, which is derived from kimchi ingredients, is used to induce malolactic fermentation by Lactobacillus species, and the progression of malolactic fermentation can be controlled through KSs. Our results suggest that KSs promote the production of organic acids, and the profiling of organic acids, as well as the progress of malolactic fermentation, can be controlled by selecting the suitable KS. Overall, this study demonstrates that kimchi fermentation can be controlled more effectively if the characteristics of KS are understood and used appropriately.

Moeun Lee, Daun Kim, Ki Won Lee, and Ji Yoon Chang. J. Microbiol. Biotechnol. 2024;34:1653-9. https://doi.org/10.4014/jmb.2403.03011

The present study aimed to identify the metabolites associated with the physiological activity of kimchi‐derived lactic acid bacteria (LAB). A clear difference was observed between the 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid (ABTS) radical scavenging rates when the pyruvate content was high (273.5 ng/µL; radical removal speed 6.50% per min) and the rates when the pyruvate content had decreased (131.9 ng/µL; radical removal speed 3.63% per min). Additionally, the characteristics of LAB antioxidant activity (increase in ABTS radical scavenging activity with reaction time, low level of 2,2‐diphenyl‐1‐picrylhydrazyl radical scavenging activity) were similar to those of pyruvate‐derived activity. Hydrogen peroxide content (WiKim0124, 2.08 → 0.26; WiKim0121, 0.99 → 0.47; WiKim39, 1.93 → 0.24) and lactate dehydrogenase activity (WiKim0124, 1.53 → 0.00; WiKim0121, 0.73 → 0.01; WiKim39, 1.72 → 0.02) decreased more in heat‐killed LAB than in non‐heat‐killed LAB. Accordingly, this resulted in increased pyruvate content and the inhibitory activity of lipid peroxide production increased by 2–3 times. Our findings indicate that pyruvate is one of the major metabolites regulating LAB physiological activity. Practical Application: The safety of utilizing live probiotics remains a topic of debate. To mitigate associated risks, there is a growing interest in non‐viable microorganisms or microbial cell extracts for use as probiotics. Various methods can be employed for probiotic inactivation. Heat treatment typically emerges as the preferred choice for inactivating probiotic strains in many instances. The present study shows the distinctions between inactivating lactic acid bacteria (LAB) through heat treatment and non‐heat treatment. It may serve as a valuable reference for selecting an appropriate inactivation method for LAB in industrial processes.

Starter cultures play a key role in shaping the flavor and sensory traits of kimchi during fermentation. This study compared seven Lactobacillaceae starters using metabolite profiling and electronic tongue/nose analyses. A total of 46 key compounds were identified via UHPLC-Q-Orbitrap-MS and HPLC. Principal component analysis showed that metabolite and sensory changes were mainly influenced by specific starters and fermentation stages rather than species or genus. Amino acid derivatives, including glutamic acid, aspartic acid, γ-glutamic acid, serine, and γ-aminobutyric acid, showed differing concentrations depending on the starter and were associated with umami perception. Electronic tongue results indicated increased sourness and decreased sweetness and bitterness across all samples, while umami notably increased only with a specific starter. Aroma compounds detected by the electronic nose also followed starter- and time-based patterns. These findings provide practical guidance for selecting effective starter cultures to enhance the umami-rich flavor of aged kimchi (Mukeunji).