酵素法によるデンプンの高度変換利用技術の開発

Abstract

This review summarizes three main topics from my work on enzyme application for starch processing, which is a major field of research in the development of industrial applications for enzymes. I have engaged in such research for more than 50 years, beginning in 1951 while I was with the enzyme production department of Nagase Co., Ltd. The first problem was the complete liquefaction of sweet potato suspension at high concentration using an enzyme process. With the “gradual heating method, ” a conventional method of liquefaction, the saccharified solution became turbid and it was impossible for the solution to be filtered and purified. The turbid liquid was generated by means of rearrangement of starch molecular chains that were not digested by enzymes in the process of gradual warm-up liquefaction. For the insoluble starch particles to be digisted, they had to be treated by heat at more than 120°C and have enzymes added again. As a liquefaction method to prevent generating insoluble starch particles, I developed the “Instantaneous heating method.” With this method, a starch suspension is instantaneously heated to 88-92°C with a-amylase. Since the method was inadequate for corn starch, double liquefaction was employed for the corn starch so that α-amylase could be added again after heating the starch solution at over 120°C. As thermostable α-amylase was produced and available from B. subtilis MK 385, the problem with corn starch liquefaction was solved by instantaneously heating at 100-110°C with a jet cooker. The second topic was the industrial production of glucose using an enzyme process. I started industrial production of glucoamylase originating from Aspergillus or Rhizopus and developed a saccharification method for starch to obtain 95-96% yield of glucose. The third problem was the development of isomerization from glucose to fructose. Glucose isomerase originating from Streptmyces phaeocromogenus was accumulated within a strain pellet. The cell with the enzyme was immobilized by an anion exchange resin modified with quaternary pyridine. It formed granulations, and cross-linked to boost its physical strength. Thus, continuous isomerization was developed with a tubular flow bioreactor packing the immobilized cell and production of glucose/fructose syrup as an alternative sweetening to sucrose was started.