Enhanced ethanol production from Kinnow mandarin (Citrus reticulata) waste via a statistically optimized simultaneous saccharification and fermentation process

Dried, ground, and hydrothermally pretreated Kinnow mandarin (Citrus reticulata) waste was used to produce ethanol via simultaneous saccharification and fermentation (SSF). Central composite design was used to optimize cellulase and pectinase concentrations, temperature, and time for SSF. The D-limonene concentration determined with high-performance liquid chromatography (HPLC) for fresh, dried, and pretreated biomass was 0.76%, 0.32%, and 0.09% (v/w), respectively. Design Expert software suggested that the first-order effect of all four factors and the second-order effect of cellulase and pectinase concentrations were significant for ethanol production. The validation experiment using 6 FPU gds−1 cellulase and 60 IU gds−1 pectinase at 37 °C for 12 h in a laboratory batch fermenter resulted in ethanol concentration and productivity of 42 g L−1 and 3.50 g L−1h−1, respectively. Experiments using optimized parameters resulted in an ethanol concentration similar to that predicted by the model equation and also helped reduce fermentation time.