Effect of nutrient supplementation on lactic acid production by lactic acid bacteria

Abstract

In this research, five substrates; yam, cassava, corn, potatoes and rice were used for lactic acid fermentation. The microorganisms were isolated using de Mann Rogosa and Sharpe (MRS) medium using the spread plate technique. Ten pure colonies were identified and presumptively classified using standard morphological and biochemical identification processes. After optimizing culture conditions at 35oC, pH 6.0 and fermentation time 122hrs, the effect of Tween 80 supplementation on lactic acid production was investigated. Supplementation of culture medium with Tween 80 was done at two different concentrations (3.0 g/L and 5.0 g/L) and the quantity of lactic acid produced for each concentration determined using total titratable acidity (TTA) method. Tween 80 (3.0 g/L) in the culture medium had dual effects on lactic acid production by the lactic acid bacteria. The highest quantity of lactic acid concentration was produced by Lactobacillus plantarum strain Z2 (0.62 ± 0.01 g/L) in yam fermentation, a 113.7% increase in lactic acid production capacity over that of the un-supplemented yam broth. A percentage increase of 34.5% in lactic acid production capacity was observed for same microorganism (Lactobacillus plantarum strain Z2) in supplemented cassava broth over that of the un-supplemented one. Lactobacillus pentosus strain BSR3 (SL2) produced the highest quantity of lactic acid on the supplemented potatoes broth, a percentage increase of 153% over that of the un-supplemented potatoes broth. For supplemented rice broth, the highest quantity of lactic acid (0.63 ± 0.02 g/L) was produced by Lactobacillus pentosus strain BSR3 (C3P), a percentage increase of 35.9% over that of the un-supplemented rice broth. There was increased lactic acid production by Lactobacillus pentosus strain BSR3 (C3P), Lactobacillus pentosus strain BSR3 (SL2), Lactobacillus plantarum strain FM02 in the Tween 80-supplemented corn broth. However, there were decreases in lactic acid production by Lactobacillus pentosus strain BSR3 (C3P) in cassava broth, by Lactobacillus plantarum strain Z2 in both corn and potato broths supplemented with the Tween 80 at 3.0 g/L. The addition of Tween 80 at 5.0 g/L resulted in decreased lactic acid production. The percentage reduction in descending order of lactic acid production in yam, cassava, corn, potatoes and rice broths by Lactobacillus plantarum strain Z2 were 79.3%, 83.6%, 90.9%, 70% by Lactobacillus pentosus strain BSR3 (SL2) and 86.9% (Lactobacillus pentosus strain BSR3 (C3P)) respectively. For un-supplemented broths, Lactobacillus plantarum strain Z2 produced the highest lactic acid (0.56 ± 0.35 g/L) from potatoes broth. With supplementation of broths with Tween 80 (at 3.0 g/L), lactic acid production was enhanced, with Lactobacillus pentosus strain BSR3 (SL2) producing the highest lactic acid concentration (0.76 ± 0.01 g/L) from potato broth. It is recommended, for large-scale production of lactic acid, that potatoes broth be fermented with Lactobacillus pentosus strain BSR3 (SL2) under the optimized culture conditions.