Optically Pure L-Lactic Acid Production Directly from Leftover Bits and Pieces of Potato Starch Using an Amylolytic Pellet-Form Complex Rhizopus Oryzae ASC081

Abstract

Optically pure L-(+)-lactic acid fermentation directly from leftover bits and pieces of potato starch (LBPPS) using an amylolytic pellet-form complex Rhizopus oryzae ASC081 was studied. The complex ASC081, which have the capability for the simultaneously saccharification and production of pure L-(+)-lactic acid, was mutagenized and screened from two parent Rhizopus oryzaes As1 and As2. In the ASC081 fermentation, the variation in temperature, inoculum size, and pH obviously affected the amylolytic capacity, the L-(+)-lactic acid production and the fungal biomass formation. The addition of phytic acid and bitter salt (an alternate name: magnesium sulfate) significantly stimulated the L-(+)-lactic acid fermentation process, and enabled complete bioconversion within 90 h. A condition, LBPPS concentration 140 g/L, pH 5.2, temperature 32℃, inoculum size 15%, phytic acid addition 0.05 g/L and bitter salt addition 0.5 g/L, was favourable for the optically pure L-(+)-lactic acid production, resulting in the optically pure L-(+)-lactic acid yield of 0.12 g/1.0 g LBPPS.