Bioprocess optimization for high cell mass production of Lactobacillus acidophilus as probiotic

Abstract

Lactobacillus from the lactic acid bacteria group, mainly synonym as a good bacterium known as probiotics that give a beneficial effect on human health. Lactobacillus acidophilus is one of the important bacteria that can maintain and restore gastrointestinal microflora, rebuild the digestive system from harmful bacteria, and fight vaginal infection. However, the biomass production of this bacteria is one of the industrial challenges. Therefore, this study was carried out to maximize cell mass production through optimization of medium composition and scaling up of the process to semi-industrial scale. Twelve different media were screened for the potential effect on cell growth. The best medium was composed of (g L-1): glucose, 30; yeast extract, 6; ammonium citrate, 1; citric acid, 0.5; potassium dihydrogen phosphate (KH2PO4), 1.5; magnesium sulphate heptahydrate (MgSO4.7H2O), 0.4; manganese (II) sulphate monohydrate (MnSO4.H2O), 0.082; sodium acetate, 1; and tween 80, 1. The biomass produced in this medium reached 2.46 g L-1. Further medium optimization using one factor at a time (OFAT) and statistical method response surface methodology (RSM) improved biomass production up to 4.64 g L-1 and 5.36 g L-1, respectively. The RSM optimized medium supported biomass production by approximately 15.52 % compared to OFAT optimized medium. Thus, the RSM optimized medium was used further in a 16-L bioreactor operated in batch cultivation mode to increase cell mass production. Cultivations in the bioreactor were carried out under controlled and uncontrolled pH conditions. High cell mass production was achieved in a controlled pH bioreactor (pH 6.5) and reached 6.41 g L-1 compared to in an un-controlled pH bioreactor which produced 4.56 g L-1 only. The biomass obtained from the controlled pH bioreactor was used for microencapsulation process. The cell viability after encapsulation was 9.45 log CFU/g with 76.95 % of encapsulation efficiency. The encapsulated L. acidophilus exhibited good resistance to bile salt concentration with 77 % of cells survived at bile salt concentration of 0.3%. However, resistance to the bile salt was found to be affected by pH value as well. After two hours of treatment, cell viability was 31.84 % at pH 4, whereas, cells were completely inactivated at pH 1. Thus, it can be concluded that statistically optimized medium composed of (g L-1): glucose, 50; yeast extract, 20.91; ammonium citrate, 3.42; citric acid, 0.5; KH2PO4, 1.5; MgSO4.7H2O, 0.4; MnSO4.H2O, 0.082; sodium acetate, 1; and tween 80, 1 produced the highest biomass production under pH-controlled condition of 6.5. Microencapsulation was also a suitable approach to protect cell viability when further applied to the human gastrointestinal tract.