Production of a Laccase and Decrease of the Phenolic Content in Canola Meal during the Growth of the Fungus Pleurotus ostreatus in Solid State Fermentation Processes

Abstract

AbstractSolid state fermentation of canola meal was carried out with the fungus Pleurotus ostreatus DAOM 197961, which is a producer of laccase. The aim of this study was to examine the effects of moisture content, inoculum size, homogenisation of inoculum and particle size of canola meal on the growth of the fungus, the production of a laccase and the decrease of the content of sinapic acid esters (SAE) in a solid state process. The results showed that the optimum moisture content, which was varied in the media between 50% and 75%, for the growth and enzyme production was 60%. The initial rate of SAE content decrease was faster in the media with 70% and 75% moisture than in those with lower moisture levels. In the study of the effects of inoculum concentration in the range of 1.1 mg to 5.5 mg/g of the medium, it was found that larger amounts of biomass and enzyme were produced in the media with inoculum concentrations from 1.1 mg to 3.3 mg/g of the medium than in the media with a higher inoculum concentration. The final and approximately the same concentrations of SAE were reached at the same time regardless of the inoculum concentration. Considering that the fungus formed pellets under the conditions at which it was grown during the inoculum preparation, it was necessary to break them by homogenisation prior to their utilisation as an inoculum. The homogenisation was carried out during a period between 15s and 200s. Although higher biomass concentrations and enzyme activities were obtained in the media which were inoculated with the inoculum homogenised for 15s and 30s, the maximum enzyme activities and biomass concentrations were reached in the media inoculated with the inoculum, which was homogenised for 120s and 200s. The time of inoculum homogenisation did not influence the kinetics of the SAE decrease. When the effects of the particle size of canola meal on the process were studied, it was found that larger particles of the meal in the solid media were more favourable for the production of the biomass and enzyme, and for a faster decrease of the SAE content than those of smaller sizes. From the obtained results it can be concluded that the tested variables have a significant influence on the growth of the fungus Pleurotus ostreatus DAOM 197961, the production of laccase and the decrease of the SAE content in canola meal. The data could be useful for the development of a solid state process for the production of laccase and for the decrease of the phenolics content in canola meal.