Repeated Batch Conversion of Raw Starch to Ethanol Using Amylase Immobilized on a Reversible Soluble-autoprecipitating Carrier and Flocculating Yeast Cells

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 pH 4 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-AS spontaneously precipitated after lOmin at pH 4.D-AS was used successively for repeated ethanol production from raw starch, in which d-AS and 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 61 g, a value of which corresponds to the average ethanol productivity of 0.85 g/l/hr. The repeated ethanol production ...