Fig. 5.
Overall carbon release rate of T. reesei based on OTR and freeze assay measurements. a Overall carbon release rate calculated from the oxygen transfer rate and freeze assay measurements of the suspended full culture broth. For comparison of the two methods, the measured freeze assay carbon release rate was adapted to the initial substrate concentration in the fermentation broth and modified to account for the decrease in substrate digestibility over cultivation time using a fractal kinetic model. b Correlation of specific carbon release rate (sCRR) with initial enzyme/cellulose (E/Celli) ratio for T. reesei. The carbon release rate was calculated as a sum of glucose, cellobiose, and xylose carbon release rate of the suspended full culture broth during freeze assay. Assay conditions: 91 mM itaconic acid buffer (pH 3.7), 120 g L−1 α-cellulose, incubation time 2 h, filling volume 1.1 in 2-mL test tube, shaking frequency 900 rpm, shaking diameter 3 mm, and 30 °C. c Cellulose conversion (X) calculated based on the residual cellulose concentration and fractal kinetic model for a cultivation of T. reesei. sCRRi initial specific freeze assay carbon release rate; h, fractal exponent describing the drop in sCRRi over time