Hydrolysis, Detoxification and Alcoholic Fermentation of Hemicellulose Fraction from Palm Press Fiber

Abstract

The palm press fiber, resulting from the extraction of oil from the fruit of the oil palm (Elaeis guineensis) is an abundant agro-industrial co-product with a potential for development of biorefineries. This study evaluated the use of the hemicellulose fraction contained in the palm press fiber as a source of sugars for the production of bioethanol by Scheffersomyces stipitis. The optimal condition for hemicellulose hydrolysis, determined by response surface methodology, utilized 30% of dry biomass in 5% H2SO4 at 121 °C for 60 min, and resulted in removal of 88.4% of this polysaccharide. The soluble fraction recovered after the acid pretreatment, called hemicellulosic hydrolyzate, contained 83 g L−1 of reducing sugars. The hydrolyzate also contained 12 g L−1 of acetic acid, 489 mg L−1 of furfural and 46 mg L−1 of 5-hydroxymethylfurfural. The detoxification of the hydrolyzate with activated charcoal, overliming and a combination thereof was evaluated for removal of unwanted byproducts. The best detoxification treatment reduced the concentrations of phenolic compounds and furfural present in the hemicellulosic hydrolyzate by 96% and 99%, respectively. S. stipitis NRRLY 7124 and S. stipitis CBS 6054 were tested for the fermentation of the hydrolyzate. The highest yield of ethanol, 0.33 gethanol gsugar −1, was obtained with the NRRLY 7124 strain in the fermentation of the hydrolyzate detoxified by overliming. An estimated production of 12.1 L of ethanol per ton of palm press fiber derived solely from the hemicellulosic fraction was achieved.