Optimization of gamma-aminobutyric acid production of Lactobacillus plantarum and determination of flavor substances in gamma-aminobutyric acid-enriched fermented milk

Abstract Text: gamma-Aminobutyric acid (GABA) is a nonprotein amino acid with positive physiological properties to animals and human. Two objectives were achieved in this work: 1) optimization of the GABA production of Lactobacillus plantarum NDC 75017 isolated from traditional yoghourt in Inner Mongolia of China, 2) exploration of the flavor variations of GABA-enriched fermented milk by this strain in shelf life. High performance liquid chromatography (HPLC) and o-phthaldialdehyde (OPA) precolumn derivatization were used to determine the GABA concentrations in MRS culture media under different fermented conditions. GABA maximum accumulation increased to 3.004 folds of the original production in the following optimized condition: 75 mM L-solium glutamate (L-MSG), 20 μM pyridoxal 5’-phosphate (PLP), 3 mM CaCl₂, 3% inoculation in MRS and 48 h fermentation with the initial pH value of 4.5. In the above condition, L. plantarum NDC 75017 was cultured to be the starter of GABA-enriched fermented milk and it was stored in 4°C for 21 days. 6 typical flavor substances were measured by spectrophotometry and HPLC at 11 point-in-time during the whole storage. Diacetyl increased gradually from 3.226 to 4.975 mg/L. Acetaldehyde went up at first, peaked at the 3rd day with 8.9 g/L and went down slowly to 7.259 g/L at last. Citric acid, pyruvic acid, lactic acid and formic acid contents of fermented milk were stable without significant variations and the concentrations of them at the end of storage were 132.772 mg/L, 10.782 mg/L, 109.268 mg/L and 82.757 mg/L respectively. Compared to general fermented milk products, lower content of diacetyl and lactic acid but higher concentration of formic acid showed in the GABA-enriched fermented milk and other three flavor substances were similar between them. Results in the present study suggested that the optimized GABA-producing L. plantarumNDC 75017 could be the potential starter applied in the manufacture of fermented milk or other dairy products with healthcare functions and unique flavors. This work was supported by National Science and Technology Project (2011AA100902) and National Natural Science Foundation of China (31171718).

Keywords: gamma-aminobutyric acid, Lactobacillus plantarum, fermented milk