α-Acetolactate decarboxylase immobilized in chitosan: A highly stable biocatalyst to prevent off-flavor in beer.

In this work, we studied the covalent immobilization of α-acetolactate decarboxylase (ALDC) on glutaraldehyde activated chitosan beads for application in beers to prevent off-flavor. The immobilized preparation was characterized regarding yield, efficiency, activity recovery, thermal and pH stabilities, and operational stability in beer. The concentration of activating agent was evaluated and at the best condition an immobilization yield of 84% and activity recovery of 9.1% were verified. Optimal pH was 6.0 for free and immobilized enzymes, however, the immobilized enzyme showed higher relative activity at the tested pH, with emphasis on the pH range from 5.0 to 6.5. Besides, immobilized enzyme showed stabilization factor of almost sevenfold at 60°C compared to free form. The immobilized biocatalyst was tested in repeated batches in beer for α-acetolactate conversion to acetoin, and after 12 cycles the enzyme presented 80% of its initial activity. To date, this is the most stable immobilized preparation of ALDC reported.