Qilin Yang,Yitao Bai,Shuangping Liu,Xiao Han,Tiantian Liu,Dongna Ma,Jian Mao
Elevated levels of biogenic amines (BAs) in fermented food can have negative effects on both the flavor and health. Mining enzymes that degrade BAs is an effective strategy for controlling their content. The study screened a strain of Lactobacillus hilgardii 1614 from fermented food system that can degrade BAs. The multiple copper oxidase genes LHMCO1614 were successfully mined after the whole genome protein sequences of homologous strains were clustered and followed by homology modeling. The enzyme molecules can interact with BAs to stabilize composite structures for catalytic degradation, as shown by molecular docking results. Ingeniously, the kinetic data showed that purified LHMCO1614 was less sensitive to the substrate inhibition of tyramine and phenylethylamine. The degradation rates of tyramine and phenylethylamine in huangjiu (18% vol) after adding LHMCO1614 were 41.35 and 40.21%, respectively. Furthermore, LHMCO1614 demonstrated universality in degrading tyramine and phenylethylamine present in other fermented foods as well. HS-SPME-GC-MS analysis revealed that, except for aldehydes, the addition of enzyme treatment did not significantly alter the levels of major flavor compounds in enzymatically treated fermented foods (p > 0.05). This study presents an enzymatic approach for regulating tyramine and phenylethylamine levels in fermented foods with potential applications both targeted and universal.
Jinsong Zhang,Youzhi Zhou,Ke Liu,Jianlin Chu,Yewei Zhang,Bingfang He
A novel nucleoside 2′-deoxyribosyltransferase ( Lh NDT) from Lactobacillus hilgardii ZJS01 was cloned and expressed in Escherichia coli BL21 (DE3). The amino acid sequence of Lh NDT displayed the highest identity of 26% to other reported NDTs. Lh NDT was a monomer as revealed by gel filtration chromatography with or without addition of Ca 2+ in elution buffer. This enzyme showed a high activity and stability over a broad pH range and was sensitive to temperature. With the addition of 15 mM Ca 2+ , the thermostability of Lh NDT was greatly promoted by 63 times and 46 times at 30 °C and 35 °C, respectively. With the use of 2′-deoxyuridine as sugar donor at an economic molar ratio of 1:1, 5-aza-2′-deoxycytidine (46%) and 5-fluoro-2′- deoxycytidine (58%) were efficiently synthesized from 5-azacytosine and 5-fluorocytosine, respectively, by Lh NDT for 2 h.
Zou Xiao-Zhou,Gong Lu-Chan,Li Ting-Ting,Lv Shu-Yi,Wang Jun
γ-Aminobutyric acid (GABA) is a crucial neurotransmitter with wide application prospects. In this study, we focused on a GABA-producing strain from a traditional Chinese fermented beverage system. Among the six isolates, Lactobacillus hilgardii GZ2 exhibited the greatest ability to produce GABA in the traditional Chinese fermented beverage system. To increase GABA production, we optimized carbon sources, nitrogen sources, temperature, pH, and monosodium glutamate and glucose concentrations and conducted fed-batch fermentation. The best carbon and nitrogen sources for GABA production and cell growth were glucose, yeast extract and tryptone. Gradual increases in GABA were observed as the glucose and monosodium glutamate concentrations increased from 10 g/L to 50 g/L. During fed-batch fermentation, lactic acid was used to maintain the pH at 5.56, and after feeding with 0.03 g/mL glucose and 0.4 g/mL sodium glutamate for 72 h, the GABA yield reached 239 g/L. This novel high-GABA-producing strain holds great potential for the industrial production of GABA, as well as the development of health-promoting functional foods and medical fields.
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