No abstract

To develop starters for the production of functional foods or materials, lactic acid bacteria producing γ-aminobutyric acid (GABA) were screened from jeotgals, Korean fermented seafoods. One isolate producing a high amount of GABA from monosodium L-glutamate (MSG) was identified as by 16S rRNA gene sequencing. M5 produced 18.47 ± 1.26 mg/ml GABA when incubated for 48 h at 37°C in MRS broth with MSG (3% (w/v)). A gene encoding glutamate decarboxylase (GAD) was cloned and overexpressed in BL21 (DE3) using the pET26b (+) expression vector. Recombinant GAD was purified through a Ni-NTA column and the size was estimated to be 53 kDa by SDS-PAGE. Maximum GAD activity was observed at pH 4.5 and 55°C and the activity was dependent on pyridoxal 5'-phosphate. The and values of GAD were 3.26 ± 0.21 mM and 0.0120 ± 0.0001 mM/min, respectively, when MSG was used as a substrate. M5 secretes a lot of GABA when grown on MRS with MSG, and the strain is useful for the production of fermented foods containing a high amount of GABA.

The effects of purified salt (PS) and mineral-rich sea salt (MRS), both with different mineral profiles, on kimchi fermentation were studied using a culture-dependent 16S rRNA sequencing technique and mass-based metabolomic analysis. The different mineral profiles in the fermentation medium caused changes in the bacterial profiles of the 2 kimchi products. An increase of Leuconostoc species in MRS-kimchi decreased the Lactobacillus/Leuconostoc ratio, which led to changes in metabolites (including sugars, amino acids, organic acids, lipids, sulfur compounds, and terpenoids) associated with kimchi quality. Although further studies on the relationship between these salt types and kimchi fermentation are needed, these results suggested that the MRS treatment had positively affected the changes of the kimchi mineral contents, bacterial growth, and metabolite profiles, which are linked to kimchi quality.

Nine bacilli with fibrinolytic activities were isolated from doenjang, a traditional Korean fermented soy food. Among them, RSB34 showed the strongest activity and was identified as by 16S rRNA and gene sequencing. During growth on LB up to 96 h, RSB34 showed the highest fibrinolytic activity (83.23 mU/μl) at 48 h. Three bands of 23, 27, and 42 kDa in size were observed when the culture supernatant was analyzed by SDS-PAGE and 27 and 42 kDa bands by fibrin zymography. The gene encoding the 27 kDa fibrinolytic enzyme AprE34 was cloned by PCR. BLAST analyses confirmed that the gene was a homolog to genes encoding AprE-type proteases. was overexpressed in BL21(DE3) using pET26b(+). Recombinant AprE34 was purified and examined for its properties. The and values of recombinant AprE34 were 0.131 ± 0.026 mM and 16.551 ± 0.316 μM/l/min, respectively, when measured using an artificial substrate, -succinyl-ala-ala-pro-phe--nitroanilide. was overexpressed in WB600 using pHY300PLK. transformants harboring pHYRSB34 (pHY300PLK with) showed higher fibrinolytic activity than RSB34.

Kimchi was prepared with different types of salts: purified salt (PS), solar salt aged for 1 year (SS1), aged for 3 years (SS3), and bamboo salt (BS). Kimchi inoculated with P30 (starter kimchi), and control kimchi (non-starter kimchi) were prepared, and stored at - 1 °C for 20 weeks. Titratable acidity values increased slowly and reached 0.96-1.01% (pH 3.73-3.83) at 20 weeks. Proportions of coccus-type lactic acid bacteria (LAB) among total LAB were higher in SS kimchi than PS kimchi. Among non-starter kimchi, the proportions were 44.7, 41.6, 29.7, and 32.1% for SS3, SS1, BS, and PS kimchi, respectively, at 2 weeks, and 11.5, 12.8, 6.7, and 5.8%, respectively, at 20 weeks. SS kimchi had much less yeast counts than PS kimchi. Among starter kimchi, yeasts were detected from PS kimchi at 10 weeks but not detected until 18 weeks from SS1 and BS kimchi and 20 weeks from SS3 kimchi.