Production of soluble sugar from cellulosic materials by repeated use of a reversibly soluble‐autoprecipitating cellulase

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Abstract
A reversibly soluble-autoprecipitating cellulase was prepared by covalently immobilizing Meicelase on an enteric coating polymer (AS-L, hydroxypropyl methylcellulose acetate succinate). The immobilized enzyme (M-AS) was reversibly soluble-insoluble depending on the pH of the reaction medium. Moreover, the enzymatic activity of M-AS, in a soluble state, for microcrystalline cellulose was higher than that of the conventional solid immobilized enzyme. On the other hand, M-AS, in an insoluble state, and good properties of self-sedimentation, and a large portion of M-AS spontaneously precipitated for about 15 min at pH 3.8. In the repeated hydrolysis of rice straw, delignified with sodium hydroxide using a bioreactor with a conical bottom, M-AS was separated batchwise from a production solution by self-sedimentation in a conical bottom of the bioreactor. When delignified, rice straw was hydrolyzed repeatedly by reuse of M-AS; the total amount of soluble sugar produced from 5 g of delignified rice straw was 2.7 g. Further, by the hydrolysis method with repeated removal of reaction inhibitors (soluble sugar), the time required for converting the same amount of delignified rice straw to soluble sugar was significantly reduced, as compared with that by the standard reaction method.