L-Lactic Acid Production from Potato Waste by a Membrane Reactor with Ultrafiltration System

Abstract

Simultaneous saccharification and fermentation (SSF) of potato waste from starch refinery into L-lactic acid was investigated. In a conventional SSF system, two or more kinds of microorganisms are cultivated in a single reactor, and it is very difficult to monitor the growth of each of the organisms. In this study, a membrane reactor system for SSF was developed. This consists of a reactor for starch hydrolysis and a reactor for lactic acid production. Medium was continuously circulated through the two reactors by means of tubes, while an ultrafiltration system was installed between them to confine each microorganism in one reactor. It was possible to measure the growth of each microorganism by this system. When Aspergillus awamori for starch hydrolysis and Lactococcus lactis for lactic acid production were used, the final lactic acid concentration and yield from 2.5% granular starch mesium were 11.3g/l and 0.72, respectively. This yield value is higher than those reported to date, and shows that this novel SSF system is very efficient for lactic acid production. In the medium containing 3% starch extracted and condensed from potato waste, the final lactic acid concentration was 6.3g/l and the yield was 0.36. In order to improve the yield, it is necessary to determine the optimal culture conditions for agitation speed, dissolved oxygen concentration, time to start the substrate circulation and a ratio of substrate volume in the two reactors.