Physiological Characteristics and GABA Production of Lactobacillus acidophilus RMK567 Isolated from Raw Milk

In order to develop a new starter for fermented milk, 2082 bacteria were isolated from raw milk. The strain that showed excellent acid forming and gamma-aminobutyric acid (GABA) production (711.40 mu g/g D.W) characteristics after incubation at 37 degrees C for 18 hr was selected and identified as Lactobacillus acidophilus by the result of API carbohydrate fermentation pattern and 16S rDNA sequence. L acidophilus RMK567 was investigated for its physiological characteristics. RMK67 strain showed good GABA production compared with commercial lactic acid bacteria. The optimum growth temperature of L. acidophilus RMK567 was 40 degrees C and cultures took 15 hr to reach pH 4.3. L. acidophilus RMK567 showed higher sensitivity to penicillin-G, novolbiocin, as compared to other 14 different antibiotics. However, it showed more resistance to kanamycin, neomycin, streptomycin. It showed higher leucine arylamidase and P-galactosidase activities compared to 16 other enzymes. It was comparatively tolerant to bile juice and able to Survive at pH 2 for 3 hr. It showed resistence to Escherichia coli, Salmonella typhimurium and Staphylococcus aureus with rates of 29.2%, 39.1% and 51.4%, respectively. Based on these and previous results, L. acidophilus RMK567 Could be an excellent starter culture for fermented milk with excellent GABA contents.