Pretreatment effects on orange processing waste for making ethanol by simultaneous saccharification and fermentation

Citrus processing waste (CPW) pretreated under different times, pH and temperatures was investigated. Pretreatments at 160 °C for longer than 4 min with steam purging were needed to remove limonene, an inhibitor for fermentation, to below 0.1%. While hemicelluloses were solubilized well following all pretreatments at 160 °C, just 70% of the pectin was solubilized in natural CPW compared to over 80% after pretreatments using acid modified CPW (pH 2.8). Pretreatments at 160 °C on base modified CPW (initial pH 6.8) quickly destroyed pectin, had significantly lower dissolved solids, and were excessively viscous. Total sugars fermentable by Saccharomyces cerevisiae were not changed after pretreatment at 160 °C for up to 8 min in CPW between pH 2.2–8.2. Ethanol yields based on sugar content after enzymatic hydrolysis after 48 h simultaneous saccharification and fermentation ranged from 76% to 94%. Ethanol yields were slightly lower but not statistically different using base modified pretreatments.