Ultrasound-assisted fermentation for enhancing metabolic and probiotic activities of LactoBacillus brevis

This study investigated the changes in metabolic and probiotic activities of .Lactobacilluse brevis (LMG 6906) throughout ultrasound-assisted fermentation. Moderate ultrasound treatments (23 kHz, 10 µm amplitude for 3main and 5 min) resulted in up to 1.09 log CFU/mL increase in Lb. brevis cell counts, 58.17 - 82.59% increase in specific growth rate, and 16 - 36.25% increase in cell membrane permeability. This was accompanied by a lower pH of 0.51, a higher titratable acidity of 0.95 mg/L, and up to 36.42% increase in protein hydrolysis with a 0.26 g/L (31.76%) increase in GABA yield. However, a higher ultrasound intensity (15 µm amplitude) was relatively lethal for Lb. brevis that led to a lower metabolic activity i.e., 0.25 - 0.30 g/L (30.58 - 36.47%) reduction in GABA yield. The Fourier transform infrared spectroscopy indicated Lb. brevis cells exposed to the sonication undergo damage or conformational/compositional alterations in DNA/RNA, cellular proteins, cell membrane, and cell wall, however, further studies are required to permit a better employment of this tool in cellular study. We speculate that low intensity ultrasound is applicable for manufacturing GABA-rich fermented products by Lb. brevis as a probiotic supplement.