Supplementation of whey with glucose and different nitrogen sources for lactic acid production by Lactobacillus delbrueckii

Lactobacillus delbrueckii was grown at room temperature in static culture. When whey (total sugar 30 g l −1) was supplemented with different concentrations of yeast extract, lactic acid production increased. When glucose (20 g l −1) was added to whey, 20 g l −1 yeast extract supplementation was found to be most suitable. Among the different nitrogen sources supplemented to whey [yeast extract, peptone, soya flour, and (NH 4) 2SO 4, having the same elemental nitrogen level of 3.1 g l −1], yeast extract was the best. The effect of yeast extract could be due to its vitamin B content. Therefore, whey was supplemented with different nitrogen sources and vitamin B complex, and no significant improvement in lactic acid production was observed. As yeast extract supplementation was not economically attractive, we decided to use a proportion of (NH 4) 2SO 4 and yeast extract. When the elemental nitrogen ratio of (NH 4) 2SO 4 to yeast extract was 3:1, the substrate use and efficiency of lactic acid production were same as in whey supplemented with 20 g l −1 yeast extract.