Opuntia Extractable and Non-extractable (NEP) Residues as Co-carbon Sources for Improved Extracellular Laccase Production: Partial Purification and Characterization

Abstract

Aim: The study of laccase production by Trametes pubescens cultured on cladode extractive residues alone, and as co-carbon source with wheat, using submerged fermentation condition. Place and Duration of Study: Biotechnology Laboratory, Durban University of Technology, Durban, South Africa. Methodology: Plant extraction, submerged fermentation, enzyme activity and characterization techniques were utilized. Results: The highest laccase activity was observed at 60-80% wheat: residue ratio combinations under submerged conditions with copper and xylidine supplementation. Partially purified enzyme fractions showed similar characteristics at different temperatures and pHs. There was good retention of relative enzyme activity at temperatures near 60°C, and pH stability from pH 4.0-6.0. At optimal culture conditions laccase activity was highest at 49.01±0.21 U/ml (80% wheat: 20% residue ratio), and lower at 10.02±0.51 U/ml (80% wheat:20% NEP residue). The optimum temperature for laccase fractions was 25°C and pH optimum at 5. Highest specific activity was 3.55 U/mg of protein for the 80% wheat: 20% residue ratio laccase extract. Conclusion: These results show the potential of cladode extractable phenol residues as potential economic growth medium for laccase production, offering a new alternative use for this agro-industrial and/or laboratory by-product.