Low intensity ultrasound increases the fermentation efficiency of Lactobacillus casei subsp.casei ATTC 39392

• Low intensity ultrasound increased production of lactic acid, cell reproduction and substrate consumption by Lactobacillus casei.
• Low intensity ultrasound increased growth indexes such as specific growth rate and logarithmic phase duration.
• The optimum values of amplitude, and duration of the waves and peptone amount for cell reproduction were found 60%, 15 s and 10 (g/l) respectively.
• Sonication at low intensity had no adverse effect on cell morphology.
• Permeat and its products can be used in production of lactic acid and led to decreasing of production costs.

l-Lactic acid (L-LA) is one of the microbial products with several applications and its production efficiency is so important. In the present study, we have been exploring application of low intensity ultrasound technology to improve the metabolic activity for l-lactic acid production by Lactobacillus casei in different mediums. L-LA, biomass production and substrate (protein) consumption were measured as parameters of fermentation yield. L-LA and protein contents were determined using the titratable acidity and the biuret method respectively. Spectrophotometry (OD600 nm) was used for measuring cell growths. L-LA, biomass production and protein consumption considered as dependent variables, but the amplitude of waves (20%, 40% and 60%), waves duration (15, 30, 45 s) and add of peptone (2, 6 and 10 g/l) as independent variables. The results showed that L-LA, biomass production and substrate consumption significantly increased (≈25%). Optimum conditions for biomass production was amplitude of 60%, 15 s exposure time and 10 g/l peptone, while for acid lactic production and substrate consumption was 40%, 30s and 6 g/l peptone, respectively. Flowcytometry analysis also showed that sonication led to increasing cell membrane permeability. This observation shows low intensity ultrasound as a potential parameter in the improvement of metabolic activity of L. casei.