3.1. The growth and acidification performance L. plantarum B1-6
Fig. 1 shows the microbial counts and the acidity of mung bean milk (MBM) as affected by sucrose concentration, inoculums concentration, fermentation time and temperature. Sucrose can act as external carbon source for LAB, thus had an influence on both the acidity and microbial growth (Fig. 1a). Microbial counts peaked when sucrose concentration was 3% and a value of 8.88 log cfu/mL was obtained. This was in accordance with the results of the acidity, for which 3% of sucrose addition afforded the highest acidity of 43.4 °T. Varied inoculum concentrations seemed to possess little effect on the final LAB viable counts, but significantly (P < 0.01) affected the acidity of final MBM. The acidity increased steadily from 33.0 °T to 48.3 °T when inoculum concentrations increased from 1% to 5%, and the further increment of inoculum concentration to 6% resulted in a slight decrease of viable counts. Temperature strongly influenced both microbial growth and acidity, and both of which showed the highest values when incubation temperature was up to 36 °C. Higher temperature however, had led to a sharp decrease of both microbial growth and acidity. This indicated that 36 °C was the optimum temperature for growth of L. plantarum B1-6 in MBM. At different fermentation duration, acidity peaked at 3 h of incubation (46.13 °T), whereas microbial growth raised and reached to its highest value at 5 h of incubation time. The number of viable cell decreased thereafter, whereas no further significant changes of acidity was observed during this period.