GABA productivity in yoghurt fermented by freeze dried culture preparations of lactobacillus acidophilus RMK567

Abstract

γ-Aminobutyric acid (GABA) producing lactic acid bacteria, Lactobacillus acidophilus RMK567 was cultivated in 50 L of sterilized MRS broth using a fermenter at 40°C for 24 h. The cell number was increased to 10.04±0.13 Log CPU/mL with a growth rate constant (k) of 0.454 generation/h and a generation time (g) of 2.303 h after a lapse of a lag phase (L) of 5.16 h. A total of 487 g of cell paste with 40.5% moisture was harvested with viable cell number of 12.48 Log CFU/g cell paste. The cell pastes after preparation with glycerol, glucose, and polydextrose as cryo-protectants were lyophilized under a vacuum of 84 m torr. A total of 408 g of freeze dried (FD) cell powders were mixed with a commercial strain of Streptococcus thermophilus to prepare of three types FD starter cultures with the viable cell numbers of 12.42 (FDA-GY), 12.60 (FDBGG) and 12.91 (FDC-GP) Log CFU/g. During preservation the FD cultures at -18°C, the cell viability of the FD starter cultures were rapidly dropped to below 3.24% of the day of storage. No significant difference was found in the cell viabilities among three types of FD starters cultures, but significant difference (p<0.01) was found in storage periods. Yoghurts fermented through FD starter culture of L. acidophilus RMK567 were determined to contain 155.16±8.53 ppm, 243.82±4.27 ppm, and 198.64±23.46 ppm of GABA, respectively. This study shows that GABA production activity of L. acidophilus RMK567 is not affected during the freeze drying process and would be available for commercial production of yoghurt containing high GABA content.