Effects of high sugar concentration and nitrogen sources on L-lactic acid fermentation using Lactobacillus rhamnosus

A homofermentative strain,Lactobacillus rhamnosus was domesticated to produce L-lactic acid with high(efficiency) and productivity under high sugar and lactic acid(concentrations).After 120 h of fermentation in flasks,using yeast extract as the nitrogen source and growth factors,120 g/L and 146 g/L of glucose were converted to L-lactic acid of 104 g/L,and 117.5 g/L,respectively.At high sugar concentration,the increasement of inoculation volume from 5% to 15 %,reduced the fermentation period but the L-lactic acid production was not obviously increased.The initial lactic acid(concentration) over 30 g/L strongly inhibited the cell growth and L-lactic acid production.When initial lactic acid(concentration) was increased to 70 g/L,cell growth and L-lactic acid production were completely stopped.Yeast extract was the best nitrogen source,while the other tested nitrogen sources reduced the cell growth and lactic acid production.Cheap soybean flour supplemented with a mixture of vitamins could replace the relatively expensive yeast extract in culture(medium) for maintaining the level of L-lactic acid production.