Integrated bioconversion of starchy and hemicellulosic fractions of macauba oil presscake into ethanol by nonconventional yeasts

Abstract Co‐fermentation of hexoses and pentoses from plant biomass to ethanol is a strategy to increase ethanol production from lignocellulosic materials and add value to residues from agroindustrial chains. The macauba ( Acrocomia aculeata ) is an oleaginous palm‐tree species considered to contribute to development in some regions of Brazil. Oil extraction from its fruits generates large amounts of presscake, which is rich in starch and hemicellulose. In this work, the production of second‐generation ethanol from sugars released by acid hydrolysis of these polysaccharides was examined. The strains Sungouiella akabanensis UFVJM R131, Spathaspora passalidarum NRRL Y‐27907, and Kluyveromyces marxianus CCT 7735 were evaluated as unconventional pentose‐fermenting yeasts. Hydrolysis of macauba presscake with dilute H 2 SO 4 produced a solution containing 17.2 g L −1 glucose, 15.0 g L −1 xylose, and 2.1 g L −1 arabinose. All yeast strains were able to utilize glucose and xylose, with clear differences in sugar conversion kinetics. The 5‐hydroxymethylfurfural (HMF) in the hydrolysate delayed sugar consumption by S. akabanensis and S. passalidarum . However, all HMF and furfural were biotransformed by all strains after 12 h. Ethanol yields ( Y P / S ) were not significantly different among strains, averaging 0.38 g g −1 , which was 25% higher than the theoretical ethanol yield associated exclusively with glucose conversion. The K. marxianus CCT 7735 lineage showed about twice the volumetric productivity of the others, probably due to its tolerance of HMF.