Optimization of medium and cultivation conditions for D-lactic acid production using cassva starch

Abstract

In this research, seven standard strains of lactic acid bacteria will be screened at first to evaluate their capability to produce D-lactic acid. Selected for investigation based on their D-lactic acid production capability with three media (MRS, RAM, BASAL).The results indicated that, all strains could produce lactic acid but at different yields. These isolates provided the concentration of lactic acid ranging from1.24-2.51, 0.44-3.24-0.49-2.10[g/l] and total acidity expressed ranging from 0.53-1.28, 0.61-1.97 and 0.69-1.58% in the three medium respectively. The maximum D-lactic acid 4.44[g/L] was obtained at 48hours fermentation with an initial cassava starch concentration. Therefore, 10 [g/L] of cassava starch concentration was chosen to be used as the inexpensive carbon source in RAM medium for D-lactic acid production by the isolate (Lactobacillus delbruekii).For nitrogen sources effect of different nitrogen sources on D-lactic acid production was investigated during this study (Lactobacillus delbruekii) was cultivated with 4-5 [g/L] yeast extract, Peptone. Yeast extract showed the higher D- lactic acid production followed by Peptone from 4.30 [g/L], 4.22 [g/L] respectively. For Dipotassium phosphate (K2HPO4) source. The maximum yield was 4.75[g/L] of D-lactic acid was produced. The process optimization will be started by optimization of medium composition using un-optimized medium and optimized medium, followed by complete growth kinetics studies in shake flask level. Result showed The D-lactic acid produced was in un-optimized medium and optimized medium 3.25[g/L], 5.47[g/L] respectively. Shake flask level scaled up in 16-L bioreactor for the production of D- lactic acid by using two strategy cultivations, with controlled pH and without controlled pH. The final results after 48 hours cultivation as follows, 9.12[g/L], 14.25[g/L] respectively, for the production of D- lactic acid.