Continuous biotransformation of pyrogallol to purpurogallin using cross‐linked enzyme crystals of laccase as catalyst in a packed‐bed reactor

Cross‐linked enzyme crystals (CLEC) of laccase were prepared by crystallizing laccase with 75% (NH 4 ) 2 SO 4 and cross‐linking using 1.5% glutaraldehyde. The cross‐linked enzyme crystals were further coated with 1 mmol L −1 β‐cyclodextrin by lyophilization. The lyophilized enzyme crystals were used as such for the biotransformation of pyrogallol to purpurogallin in a packed‐bed reactor. The maximum conversion (76.28%) was obtained with 3 mmol L −1 pyrogallol at a residence time of 7.1 s. The maximum productivity (269.03 g L −1 h −1 ) of purpurogallin was obtained with 5 mmol L −1 pyrogallol at a residence time of 3.5 s. The productivity was found to be 261.14 g L −1 h −1 and 251.1 g L −1 h −1 when concentrations of 3 mmol L −1 and 7 mmol L −1 respectively were used. The reaction rate of purpurogallin synthesis was maximum (2241.94 mg purpurogallin mg −1 CLEC h −1 ) at a residence time of 3.5 s, when 5 mmol L −1 pyrogallol was used as the substrate. The catalyst to product ratio calculated for the present biotransformation was 1:2241. The CLEC laccase had very high stability in reuse and even after 650 h of continuous use, the enzyme did not lose its activity. Copyright © 2006 Society of Chemical Industry