Green biocatalysis: coconut fibre-immobilized laccase in efficient degradation of tannic acid.

This study optimizes laccase production from Beauveria pseudobassiana PHF4 using response surface methodology (RSM), followed by enzyme immobilization on coconut fibres for tannic acid degradation. Central composite design identified optimal conditions (yeast extract concentration of 2.5% (w/v), pH 6.5, glucose concentration of 2.5% (w/v) and incubation time of 6.5 days), leading to a 2.26-fold increase in laccase activity (48.67 U/ml). The partially purified laccase was immobilized on coconut fibres, and effects of various physiochemical factors were studied. The optimal pH for both free and immobilized laccase was observed to be 5.0. The optimal temperature for free and immobilized laccase was found to be 25 °C and 30 °C, respectively. Additionally, the optimal substrate concentration was observed to be 2 mM for free laccase and 3 mM for immobilized laccase. Retention of 82.51% enzyme activity for free enzyme on the 16th day and 18.91% activity on the 20th day of storage was observed. For immobilized enzyme, 83.44% of activity was retained up to the 16th day, and 30.36% activity was observed on the 20th day of storage. The immobilized enzyme exhibited impressive reusability, retaining approximately 85.87% of enzyme activity over the course of 4 cycles. During HPLC analysis, 79.60% of tannic acid degradation was found after 24 h.