This study was aimed to identify and optimize the culture conditions for gamma-aminobutyric acid (GABA) production by a lactic acid bacterium strain isolated from mam nem , a fermented fish sauce. Among the six isolates obtained from mam nem , the MN12 had the most potent GABA-producing capability. The strain was then identified to be Pedioccocus pentosaceus by employing MALDI-TOF-MS and phenylalanyl-tRNA synthase sequencing methods. The initial cell density of 5.10 6 CFU/mL, monosodium glutamate concentration of 60 mM, initial pH of 7, temperature of 45°C and cultivation time of 72 h were found to be the optimal culture conditions for highest production of GABA, reaching 27.9 ± 0.42 mM, by this strain. The cultivation conditions for GABA production by P. pentosaceus MN12 have been successfully optimized, providing a foundation for the development of fermented foods enriched with GABA.

In this study, we evaluated the effect of probiotic bacteria Pediococcus pentosaceus supplemented at different inclusion levels in a control diet [basal diet containing 0.5% fructooligosaccharide (FOS)] on the growth performance, feed conversion ratio, immune response, and the disease resistance of whiteleg shrimp Litopenaeus vannamei juveniles against Vibrio parahaemolyticus. A control diet with 0.5% FOS but without P. pentosaceus supplementation (Control) was prepared. In addition, three other test diets were also formulated: control diet supplemented with P. pentosaceus at (i) 1 × 106 cfu g–1 diet (P1), (ii) 1 × 107 cfu g–1 diet (P2), or (iii) 1 × 108 cfu g–1 diet (P3). After a 60-day feeding trial, the experimental shrimps were challenged with V. parahaemolyticus. The results showed that dietary supplementation of P. pentosaceus significantly improved the growth performance and immune responses of L. vannamei juveniles. The juveniles that were fed with a P2 or P3 diet recorded the maximum increase in the final body weight, final length, weight gain, and survival rate. The total hemocyte counts, phenoloxidase, and lysozyme activity of shrimp fed with either of these two diets were significantly enhanced. The results also showed that juveniles fed with a P2 or P3 diet exhibited significantly lower mortality when challenged with V. parahaemolyticus. Overall results suggested that a combination of P. pentosaceus at the inclusion level of 1 × 107 cfu g–1 diet (P2) and 0.5% FOS could be considered as a potential synbiotic formulation for improving the growth, health, and robustness of L. vannamei.

Strain Lactobacillus fermentum MC3 isolated from fermented bamboo shoots was used in this study. This isolate had a high exopolysaccharide (EPS) production capability. It was inoculated in the medium with a supplement of various concentrations of carbohydrate source (2, 3, 4, 5, and 6% (w/v)). The mixtures were then cultured under different conditions of initial cell density, temperatures, pH, and incubation time to identify the optimum parameters for the EPS biosynthesis of this strain. The EPS yield was measured using the phenolsulfuric acid method. The results showed that adding glucose, lactose, and sucrose to the culture medium significantly increased the EPS production with a maximum amount of 4% of sugars. The yield was the highest for glucose at 178.207 mg/L, and the obtained figures for lactose and sucrose were 148.614 mg/L and 152.272 mg/L, respectively. The results indicated that the EPS production by L. fermentum MC3 reached the maximum values at 200.728 mg/L in the medium supplemented with 4% glucose at 40 °C, pH 6.0, and initial cell density of 10 6 CFU/mL for 48 h cultivation. By methylation and gas-chromatography mass spectrometry (GC-MS), it was found that the exopolysaccharide is composed of D-mannose, D-glucose, and D-galactose at the molar ratio of 1:0.74:0.09. 10 min, 4 °C). The supernatant was precipitated with two volumes of chilled absolute ethanol.After standing overnight at 4 °C, the resultant precipitate was collected by centrifugation (12 g, 20 min, 4 °C), dissolved in distilled water, dialyzed against distilled water at 4 °C for 24 h, and lyophilized. The total of EPS (expressed as mg/L) was estimated in each sample with the phenol-