5-06: Use of palm kernel press cake for production of bioethanol and feed

Palm kernel press cake (PKC) is a residue from palm oil extraction, composed mainly of polysaccharides from cell-wall material, of which the carbohydrate mannan is the most predominant. Due to increased demand for plant oils globally there has been a tremendous increase in palm oil production in recent years. In Indonesia and Malaysia large amounts of palm kernels are processed at centralised plants, which make PKC an ideal feedstock for further processing into e.g. bioethanol or other biorefinery processes. At present the PKC is only used for feeding purpose, but due to the high content of mannan, it cannot be included in high amounts in broiler diets.  
Mannose can readily be fermented to ethanol by normal yeast Saccharomyces cerevisiae. The first step in the conversion of PKC is then an efficient hydrolysis of polymers, mainly mannan, into fermentable monomers. The present study examines the pretreatment requirements and especially the enzymatic hydrolysis of polysaccharides from the cell-wall material present in PKC by various enzyme preparations in order to achieve high amounts of free monosaccharides. The process has been tested at high solids concentrations and it was possible to operate at up to 50% DM. The resulting hydrolysates were easily fermented by Saccharomyces cerevisiae with high ethanol yields. Various process configurations (SHF and SSF) were also tested. In addition, the processing of PKC resulted in a new feed product with increased protein content, which could be beneficial for the feeding value of this new residue.