Biodegradation of Lignin in Oil Palm Fronds by White Rot Fungi

Abstract

Oil palm fronds are a by-product from the harvest of the fresh fruit from oil palms. Nowadays, oil palm fronds are used as a source of roughage for ruminants. However, the effective use of the fronds is limited by poor nutrient composition, mainly due to their high lignin and low protein levels. White rot fungi, which degrade cellulose, hemicellulose and lignin, are widely used to increase the digestibility of agro-residues. In this research, 63 fungal isolates of white rot fungi in Thailand were sampled and screened for their production of ligninolytic enzymes by the agar plate screening method. The results showed that 48 isolates could produce laccase, manganese peroxidase and/or lignin peroxidase. A total of 27 isolates that exhibited high ligninolytic enzyme activity were selected to study the lignin degradation in oil palm fronds by solid-state fermentation. It was found that only 7 isolates: OP04, OP06, OP13, OP16, OP47, OP53 and OP61 could reduce lignin in oil palm fronds from 30% down to 15–18% within 30 d at 30 °C and OP06 showed the highest laccase and manganese peroxidase activities (mean ± SD) of 0.896 ± 0.02 and 0.799 ± 0.07 U/g of dry weight, respectively, where one unit (U) of enzyme activity was defined as the amount of enzyme catalyzing the oxidation of 1 μmol of substrate per minute.