Phenyllactic acid (2-hydroxy-3-phenyl propionic acid; PLA) is a natural antibacterial compound derived from phenylalanine catabolism. PLA shares a metabolic pathway with lactic acid (LA) and is metabolized by the glycolytic enzyme, lactate dehydrogenase, during fermentation. In this study, we identified PLA in fermented kimchi and investigated its relationship with kimchi-derived lactic acid bacteria (LAB) during kimchi fermentation using liquid chromatography-mass spectrometry. PLA was detected in four kimchi samples to different extents depending on the initial glucose concentration and fermentation stage, indicating a link between bacterial growth and PLA production. PLA content in the kimchi was 12.0–21.1 μg/ml at the early stage and decreased to 4.8–9.5 μg/ml at 3 or 4 weeks. PLA production in LAB was associated with the presence of lactate dehydrogenase genes, and differed from lactic acid production. Bacteria lacking the d-lactate dehydrogenase gene (2-Hacid dh) did not produce PLA. Addition of Lactobacillus plantarum enhanced PLA production 1.7-fold, reaching a maximum at 14 days. Lactobacillus brevis and Leuconostoc lactis caused increases of approximately 1.5-fold compared to the control. These results suggested that addition of specific LAB to kimchi as starter cultures can increase PLA content, and has great potential to enhance safety of the food product.
The focus of this study was the mechanism of starch accumulation in Chlamydomonas reinhardtii high-starch mutants. Three C. reinhardtii mutants showing high-starch content were generated using gamma irradiation. When grown under nitrogen-deficient conditions, these mutants had more than twice as much starch than a wild-type control. The mechanism of starch over-accumulation in these mutants was studied with comparative transcriptome analysis. In all mutants, induction of phosphoglucomutase 1 (PGM1) expression was detected; PGM1 catalyzes the inter-conversion of glucose 1-phosphate and glucose 6-phosphate in both starch biosynthetic and glycolytic pathway. Interestingly, transcript levels of phosphoglucose isomerase 1 (PGI1), fructose 1,6-bisphosphate aldolase 1 and 2 (FBA1 and FBA2) were down-regulated in all mutants; PGI1, FBA1, and FBA2 act on downstream of glucose 6-phosphate conversion in glycolytic pathway. Therefore, down-regulations of PGI1, FBA1, and FBA2 may lead to accumulation of upstream metabolites, notably glucose 6-phosphate, resulting in induction of PGM1 expression through feed-forward regulation and that PGM1 overexpression caused starch over-accumulation in mutants. These results suggest that PGI1, FBA1, FBA2, and PGM1 correlate with each other in terms of coordinated transcriptional regulation and play central roles for starch over-accumulation in C. reinhardtii.
The histidine-tagged protein binding capacity and purification efficiencies of TSMNPs (terpyridine receptor-immobilized silica-coated magnetic nanoparticles) is described.
Three cystein-tagged cellulases co-immobilized on AuNP and Au-MSNP for the hydrolytic degradation of cellulose. The biochemical properties, stabilities, activities and reusability of these co-immobilized systems were compared to those of mixtures of free cellulases.
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Kimchi is a traditional Korean salted spontaneous lactic acid bacteria (LAB)-fermented food made using various vegetables. Organic acids, free sugars, and amino acids are key metabolites produced during LAB fermentation that determine the taste and quality of kimchi. However, each metabolite is typically analyzed using an independent analytical method, which is time-consuming and expensive. Therefore, in this study, we developed a method based on LC-Q-Orbitrap MS using which 20 types of representative fermented kimchi metabolites were selected and simultaneously analyzed within 10 min. The established method was validated, and its detection and quantification limits, linearity, precision, and accuracy were found to satisfy the Association of Official Agricultural Chemists (AOAC) validation guidelines. The 20 metabolites were simultaneously extracted from kimchi with different degrees of fermentation and quantitatively analyzed using LC-Q-Orbitrap MS. These results were analyzed using linear discriminant analysis and heat mapping, and the metabolites were grouped into early, middle, and late stages of fermentation. Malic acid (6.518-7.701 mMol) was only present in the initial stage of fermentation, and l-phenylalanine rapidly increased from the middle stage (2.180 mMol) to late stage (4.770 mMol). Lactic acid, which is representative of the sour taste of kimchi, was detected in the middle stage and increased rapidly up to 74.452 mMol in the late stage. In summary, in this study, 20 major kimchi metabolites were accurately analyzed within 10 min and grouped based on the degree of fermentation. Therefore, the method established in this study accurately and rapidly provides information on kimchi consumption and fermentation that could be highly valuable to the kimchi industry and kimchi consumers.
This study investigated the elemental composition of three types of Raphanussativus kimchi. The analytical methods of inductively coupled-plasma mass spectrometry and inductively coupled plasma-optical emission spectroscopy were validated. A total of 25 elements including major inorganic nutrient elements, trace elements, and toxic elements were measured following the AOAC guidelines. The results revealed distinct variations according to the kimchi type (KK, YK, and CK). The CK group had the highest Na content, whereas the YK group had the highest K content. The Ca levels did not differ significantly. Zn, Sr, and Mn were present at notable quantities in all three groups. Trace amounts of three toxic elements (As, Cd, and Pb) were detected, but their levels remained below harmful limits. Heat maps and linear discriminant analysis plots confirmed distinct grouping in the elemental concentrations. These findings highlight the unique composition of each kimchi type and support the safe consumption of kimchi. This study provides valuable insights into the composition, nutritional value, and safety of kimchi, enabling further research and development in the field.
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