Continuous Lactic Acid Production from Raw Starch in a Fermentation System Using a Reversibly Soluble-autoprecipitating Amylase and Immobilized Cells ofLactobacillus casei

Abstract

Lactic acid was continuously produced from raw starch using a combination of a reversibly soluble-autoprecipitating amylase (D-AS) depending on pH and Lactobacillus casei entrapped in κ-carrageenan. Lactic acid was produced continuously by a novel reactor system, which consisted of a turbine-blade reactor with a cylindrical stainless steel net, a mixing vessel, and a separation vessel. The gel beads with entrapped lactic acid bacteria were held on the cylindrical net equipped in the main reactor throughout cultivation. D-AS was separated continuously from a solution containing lactic acid by self-sedimentation in the separation vessel and it was returned to the main reactor for repeated use. In the continuous lactic acid production from raw starch, the lactic acid productivity was 3.1 g/l/hr at a dilution rate (D) of 0.1 hr-1 and the value was about 3.1 times higher than the average of the repeated batches of lactic acid production. Although the enzymatic activity of D-AS is inactivated due to insolubilization of the enzyme by KCl accumulated during the control of pH in the reactor, it is possible to recover the enzymatic activity by replacing a part of the old broth with a new one. This continuous production system using the novel reactor system may be widely applicable to the production of useful materials from solid substrates with other microorganisms for fermentation than lactic acid bacteria.