Effects of medium high pressure treatments on protease activity

The ability of Lactobacillus manihotivorans LMG 18010 to produce l(+)-lactic acid from a high concentration of starch by direct fermentation was investigated. To improve the production of lactic acid from a highly concentrated starch, fed-batch cultures were carried out with different feeding strategies to reduce substrate inhibition. The highest lactic acid production was 71.4 g/L, which was obtained by intermittent feeding of concentrated starch media containing nitrogen sources. After 5 days of fermentation, about 87% of the substrate was consumed with a volumetric productivity of 0.6 g/L·h which is 1.8 times higher than that obtained from batch fermentation. This result clearly shows that intermittant feeding of a highly concentrated substrate solution during fermentation is an efficient way of eliminating substrate inhibition.