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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 ic-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-ASwas 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 3.1g/l/hr at a dilution rate (D) of O.lhr"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 KC1 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 maybe widely applicable to the production of useful materials from solid substrates with other microorganisms for fermentation than lactic acid bacteria.In simultaneous saccharification and fermentation of starchy raw materials, the liquefaction and saccharification steps of raw materials with enzymesare a major rate-limiting stage rather than the fermentation by microorganisms.1>2) In this article, we report on the continuous production of lactic acid from raw starch with a novel reactor system using D-AS and the lactic acid bacteria entrapped in /c-carrageenan.

A raw-starch-digesting amylase, Dabiase K-27, was immobilized covalently on an enteric coating polymer (hydroxypropyl methylcellulose acetate succinate: AS) as a carrier which is autoprecipitating in an insoluble state below pH4 as well as reversibly soluble-insoluble depending on pH. Dabiase immobilized on AS (D-AS) showed a sharp response of solubility to slight changes of pH without decrease in enzymatic activity.Moreover, D-AS in an insoluble state had good properties of sedimentation and a large portion of D-ASspontaneously precipitated after 10 min at pH 4. D-ASwas used successively for repeated ethanol production from raw starch, in which D-ASand flocculating yeast cells were separated simultaneously from a product solution by sedimentation in a reactor with a conical bottom. In the five batches of 10%raw starch, the total amount of ethanol produced from 150g of raw starch was 61g, a value of which corresponds to the average ethanol productivity of 0.85 g/l/hr. The repeated ethanol production by a combination of D-AS and flocculating yeast cells is a promising procedure for effectively using the enzyme and recovering the product solution economically in a heterogeneous culture system containing a solid substrate.

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