Optimisation of lactic acid bacterial growth for the production of Bambara groundnut probiotic beverage

28 Mar 2015

Bambara groundnut milk (BGNM) was inoculated with lactic acid bacteria (LAB) following a three-factor factorial design (4 ? 3 ? 3) consisting of probiotics (Lactobacilus acidophilus, L. bulgaricus, L. casei and L. plantarum), temperature (35, 40, 45oC) and fermentation time (6, 15, 42 h). The dependent variables of interest (pH, probiotic growth (OD), lactic acid) were modelled using quadratic polynomial and numerical optimisation was used to estimate the optimal conditions for the production of BGN probiotic beverage. The quadratic polynomial model was adequate to navigate the design space. The LAB and incubation time had a significant effect on the pH, lactic acid content and OD of the bambara groundnut milk (BGNM). Lactobacillus bulgaricus significantly (p < 0.05) reduced the pH of BGNM milk to 5.18. There was no significant effect of temperature on pH. Fermentation for 24 h significantly (p < 0.05) reduced the pH to 5.14, increased the viability of the bacteria with high absorbance of 0.1816 and increased the lactic acid production to 1.46%. There was no difference in lactic acid production between L. acidophilus and L. plantarum. The optimal condition for the production of BGN probiotic beverage was estimated to be L. bulgaricus fermented at 35oC for 24 h with a desirability of 0.854. This condition is estimated to yield a pH of 4.7 with optical density of 0.25 at 600 nm. The next promising probiotic was L. plantarum that could be fermented at 35oC for 24 h with estimated pH of 4.4 and optical density of 0.20 at 600 nm with 0.843 desirability. Thus it has been established that BGNM can support the growth of lactic acid bacteria a requirement for production of probiotic beverage.