Enhancing stability and transglycosylation efficiency of alternansucrase from Leuconostoc citreum ABK-1 by immobilization

Alternansucrase (ALT) catalyzes the transglycosylation of sucrose, synthesizing α-1,6 and α-1,3-linked glucan, and also utilizes maltose as an acceptor to produce glucooligosaccharides. In this study, alternansucrase from Leuconostoc citreum ABK-1 was immobilized on glutaraldehyde-activated chitosan beads. Immobilization parameters, namely glutaraldehyde concentration and enzyme loading, were optimized to achieve 59.7 % activity yield with an immobilized activity of 10.3 U/g bead. The immobilized ALT exhibited a broader working pH than that of free enzyme, with an optimal pH shift from 4 to 5–6. The thermostability of immobilized ALT was significantly improved, exhibiting up to a 5.4-fold increase in half-life at 37 °C. DLS analysis revealed that the immobilized ALT produced larger alternan particles, with an average diameter of 117.3 nm compared to 79.75 nm for the free enzyme, suggesting that transglycosylation efficiency was enhanced. Also, the immobilized ALT could synthesize a higher amount of isomaltose and isomaltotriose. Moreover, we found that the immobilized enzyme retained over 50 % of its initial activity after 14 reuse cycles, suggesting its potential for industrial applications of immobilized ALT due to enhanced stability and reusability.