CONTINUOUS PRODUCTION OF GLUCONIC ACID AND SORBITOL FROM SUCROSE USING INVERTASE AND AN OXIDOREDUCTASE OF ZYMOMONAS-MOBILIS

Abstract

Gluconic acid and sorbitol were simultaneously produced from sucrose using a glucose-fructose oxidoreductase of Zymomonas mobilis and invertase. Invertase was immobilized on chitin by cross-linking with glutaraldehyde, and chitin-immobilized invertase was coimmobilized with the permeabilized cells of Z. mobilis in calcium alginate beads. The optimum amounts of invertase and permeabilized cells for coimmobilization were determined, and operational conditions were optimized. In a continuous stirred-tank reactor (CSTR) operation, the maximum productivities for gluconic acid and sorbitol were found to be 4.51 and 4.60 g l-1 h-1, respectively, at a dilution rate of 0.055 h-1 and a sucrose concentration of 20%, but low operational stability was observed due to the abrasion of the beads. In order to increase the operational stability, a recycle packed-bed reactor (RPBR) was employed. In an RPBR operation, the maximum productivities for gluconic acid and sorbitol were observed to be 5.10 and 5.20 g l-1 h-1 at a dilution rate of 0.053 h-1 and a sucrose concentration of 20% when recirculated at the rate of 1,200 ml h-1. The coimmobilized enzymes remained stable for 250 h in the RPBR without any loss of activity.