Glutamate decarboxylase (L-glutamate-1-carboxylase, GAD; EC 4.1.1.15) is a pyridoxal 5-phosphate-dependent enzyme, which catalyzes the irreversible α-decarboxylation of L-glutamic acid to γ-aminobutyric acid (GABA) and CO2. The enzyme is widely distributed in eukaryotes as well as prokaryotes, where it – together with its reaction product GABA - fulfils very different physiological functions. The occurrence of gad genes encoding GAD has been shown for many microorganisms, and GABA-producing lactic acid bacteria (LAB) have been a focus of research during recent years. A wide range of traditional foods produced by fermentation based on LAB offer the potential of providing new functional food products enriched with GABA that may offer certain health-benefits. Different GAD enzymes and genes from several strains of LAB have been isolated and characterized recently. GABA-producing LAB, biochemical properties of their GAD enzymes, and possible applications are reviewed here.

Obesity and hyperglycemia can trigger various diseases, including diabetes mellitus and cardiovascular ailments. Health-promoting fermented milk products can be useful in tackling these issues. One such product is the fermented milk developed using Lactobacillus casei AP, a probiotic strain from Indonesia that has not been tested in humans thus far. Our objective was to examine the effects of L. casei AP-fermented milk products on lipid profiles, blood glucose levels and monocyte chemoattractant protein-1 (MCP-1) levels in obese adults. A total of 29 obese subjects were given L. casei AP-fermented milk products, and their fasting blood glucose, total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL) and triglyceride levels were measured using diagnostic system kits. MCP-1 levels were measured using enzyme-linked immunosorbent assay. It was determined that the administration of L. casei AP-fermented milk products significantly reduced total cholesterol, LDL and triglyceride levels (p < 0.05); however, it did not increase HDL (p > 0.05), MCP-1 or fasting blood glucose levels (p ≥ 0.05). In conclusion, in obese Indonesian adults, L. casei AP-fermented milk might reduce total cholesterol, LDL and triglyceride levels but may not affect HDL, MCP-1 or fasting blood glucose levels.

In the present study, we isolated and screened thirty strains of GABA-producing lactic acid bacteria (LAB) from Indonesian traditional fermented foods. Two strains were able to convert monosodium glutamate (MSG) to GABA after 24 h of cultivation at 37oC based on thin layer chromatography (TLC) screening. 16S rDNA sequencing and proteomic identification using MALDI-TOF MS identified these two strains as Lactobacillus plantarum designated as L. plantarum FNCC 260 and L. plantarum FNCC 343. The highest yield of GABA production obtained from the fermentation of L. plantarum FNCC 260 was 809.2 mg/l of culture medium after 60 h of cultivation. Supplementation of 0.6 mM pyridoxal 5’-phosphate (PLP) and 0.1 mM pyridoxine led to the increase in GABA production to 945.3 mg/l and 969.5 mg/l, respectively. The highest GABA production of 1226.5 mg/l of culture medium was obtained with 100 mM initial concentration of MSG added in the cultivation medium. The open reading frame (ORF) of 1410 bp of the gadB gene from L. plantarum FNCC 260 encodes 469 amino acids with a calculated molecular mass of 53.57 kDa. The production of GABA via enzymatic conversion of monosodium glutamate (MSG) using purified recombinant glutamate decarboxylase (GAD) from L. plantarum FNCC 260 expressed in Escherichia coli was found to be more efficient (5-fold higher within 6 h) than the production obtained from fermentation. L. plantarum FNCC 260 could be of interest for the synthesis of GABA.