Laccase Isoenzymes of Pleurotus ostreatus Grown at Different pH in Solid-State Fermentation Using Polyurethane Foam as Support

Abstract

Aims: Effect of culture medium pH (3.5, 4.5, 6.5, 7.5 and 8.5) on the activity and number of laccase isoenzymes of Pleurotus ostreatus grown in solid-state fermentation using polyurethane foam as a support was evaluated. Methodology: Pleurotus ostreatus was grown in solid-state fermentation using polyurethane foam as inert support at different initial pH of the culture medium. The enzymatic extracts were obtained by pressing the polyurethane foam every day of culture. The laccase activity was measured in each enzymatic extract using 2,6-dimethoxyphenol as substrate and the isoenzymes number were detected through zymograms. Results: In general, the fungus showed high values of specific growth rate grow that all pH tested, and the higher were at pH 3.5 and 8.5 (0.78 and 0.82h-1, respectively), whereas at pH6.5 was 0.034h-1 and pHs of 4.5 and 7.5 was 0.047h-1. Furthermore, the maximum biomass values were low, about 3.7g/L in all cases. The maximum values of laccase activity were observed in fermentations development at pH4.5 and 6.5 (approximately 40000 U/L). The largest number of isoenzymes was observed in fermentations carried out at pH 7.5 and 8.5. Conclusion: In solid-state fermentation on polyurethane foam, the pH of the culture medium did not affect the growth of the fungus, however, there were differences in the production and activity of laccases.