Solid-state fermentation of wheat bran by Trichoderma reesei QM9414: substrate composition changes, C balance, enzyme production, growth and kinetics

Abstract

A description is given of the solid-state fermentation of wheat bran by Trichoderma reesei QM9414 at constant temperature and relative humidity. Glucosamine, the oxygen consumption rate (OCR), the carbon dioxide production rate (CPR), changes in wheat bran composition and the production of four enzymes were measured during 125 h of fermentation. A C balance was set up between CO₂ production, based on CPR measurements, CO₂ production as expected on the basis of substrate composition changes and substrate elemental composition in combination with dry-matter weight loss. Glucosamine was used as the measure of biomass. The results indicate that the glucosamine content of fungi in liquid culture cannot be used to estimate the biomass content in solid-state fermentations. Using glucosamine, correlations between fungal growth and respiration kinetics could only partly be described with the linear-growth model of Pirt. A decline in OCR and CPR started the moment the glucosamine level was 50% of its maximum value. After the glucosamine level had reached its maximum OCR and CPR continued to decline. The activities of xylanase and protease are linearly related to the glucosamine level. No clear correlations between glucosamine and carboxylmethylcellulose-hydrolysing enzyme activity and amylase activity were found.