Abstract:Immobilized enzymes were prepared by using strongly alkaline macroporous resin, amino resin, and epoxy resin as immobilized carriers of glucose oxidase and catalase, respectively, and their effect on low-pH gluconic acid production was assessed. The results of the acid resistance test showed that all the three immobilized enzymes had stronger acid resistance than did the free enzyme. The free enzyme and the three immobilized enzymes were used to prepare gluconic acid under low pH conditions (pH value 3.5). The reaction times required for the strongly alkaline macroporous resin-immobilized enzyme, amino resin-immobilized enzyme, and epoxy resin-immobilized enzyme were 40, 24, and 27 h respectively. The enzymatic activity loss rates were 46.44%, 3.42%, and 21.84%, respectively. The free enzyme was completely inactivated during the reaction. The clarity and chromaticity of the three immobilized enzyme reaction solutions were significantly better than those of the free enzyme reaction solutions. The preparation process of amino resin-immobilized enzyme-after further optimization through orthogonal experiments - was as follows: the concentration of mixed enzyme solution was 10%, the ratio of glucose oxidase to catalase was 1.5:1, and the fixation temperature was 25 ℃. Under these conditions, the recovery rate of amino resin-immobilized enzyme was as high as 93.15%, and the conversion time of the 100 g/L glucose solution was 23 h. At the end of the reaction, the ratio of gluconic acid to sodium gluconate had reached 0.899:1 (m/m), and the amino resin-immobilized enzyme was stable. Based on these results, we conclude that the amino resin immobilized enzyme can be used to establish a low-pH immobilized enzyme gluconic acid production process, with the goal of producing high-quality gluconic acid products.
