Production of laccase by repeated batch semi-solid fermentation using wheat straw as substrate and support for fungal growth.

Repeated batch semi-solid fermentation (sSF) process using wheat straw substrate and fungal growth of Ganoderma lucidum on solid substrate was studied for production of laccase. pH showed significant effect on laccase production. Highest laccase activity with pH controlled to 5.0 in batch sSF was 15257.2 ± 353.4 U L- 1 on 9th day. In repeated batch process at pH 5.0, insoluble biomass substrate and fungal growth were reused after liquid part of medium was replaced with glucose, ammonium phosphate (best nitrogen source) and combined glucose and ammonium phosphate solution separately. Refilled to 80% w v- 1 of initial soluble sugar of first batch resulted in highest laccase production with peak activity after 4 days from replacement. Production of enzyme increased from 15257.2 U L- 1 in first batch to cumulative 90164.4 U L- 1 in 29 days after six repeated batches, productivity increased from 1680.2 to 3110.3 U L- 1 day- 1 (∼ 1.9 times) due to reductions in inhibitory effects and time required for fungal growth. Utilization of wheat straw in repeated batch sSF was supported by composition analysis and morphological changes (scanning electron microscopy) of substrate. Economic production of laccase using agricultural residues in repeated batch sSF could be possible.