The formation of isomaltulose by immobilized Erwinia rhapontici

Abstract

Recently the potential of immobilized cells for the production of biochemicals has become recognized^1,2. Here we describe a simple, stable, continuous method of converting concentrated sucrose solutions into isomaltulose using columns of Erwinia rhapontici cells entrapped in alginate gel pellets, which exemplifies several strategies for maximizing the yield and stability of immobilized cells. This method has been successfully operated on a pilot-plant scale. The isomaltulose has possible applications, which are at present being evaluated by potential users, as a non-cariogenic bulking agent in foodstuffs and phar-maceuticals^3–5. Little enzyme activity or viability was lost during immobilization and surprisingly high yields of isomaltulose were obtained. The enzyme associated with the cells was stabilized by immobilizing in alginate rather than other support materials; by using structurally intact non-growing but not necessarily viable cells rather than isolated enzyme, disrupted cells or growing cell preparations; and most dramatically, by using concentrated pure sucrose as substrate and by maintaining complete conversion of the sucrose into isomaltulose. Thus the immobilized cells were about 350 times more stable than free cells, a half life of about 8,600 h being achieved.