Reduced tannin content of laccase-treated cocoa (Theobroma cacao) pod husk

Abstract

The high levels of anti-nutritional substances such as tannin and lignin in cocoa (Theobroma cacao) pod husk hinder its proper utilization by animals. The purpose of the present study was to isolate laccase from the residual substrate of oyster mushroom (Pleurotus ostreatus) in order to investigate its potential as a tool for the degradation of lignin and tannin in cocoa pod husk. Laccase (specific activity of 7.4 mU mg-1) was extracted from spent sawdust and purified to electrophoretic homogeneity. The isolated enzyme oxidized 2,6-dimethoxyphenol optimally at pH 5.0 and showed maximum activity at 50°C. Treatment of cocoa pod husk with laccase for 40 min resulted in a 66% reduction in tannin content. Pretreatment of cocoa pod husk with laccase resulted in a higher rate of cellulose degradation in vitro. The enzyme was, however, unable to promote lignin depolymerization under the experimental paradigm employed. These findings provide an important opportunity for the isolation of laccase from the residual substrate of Pleurotus ostreatus on a commercial scale in Ghana. Treatment of cocoa pod husk with isolated extracellular laccase would reduce tannin levels considerably and thus, improve the nutritive value of cocoa pod husk-based animal feeds.