Abstract

This study was designed to determine the types of phenolics in palm kernel cake (PKC) and optimise the extraction of phenolics. The phenolics of PKC were extracted in free methanol-soluble and cell wallbound forms. Optimisation of phenolic extraction from PKC was carried out by investigating the effects of pretreatment, different solvents (water, methanol, ethanol and acetone), extraction temperatures (25°C, 60°C and 80°C) and extraction durations (15, 30, 60 and 120 minutes). The results indicated that 70.44% (500.9 μg/g of dry weight) of the phenolics in PKC were in free methanol-soluble form whereas 29.56% (210.2 μg/g of dry weight) was cell wall-bound phenolics. The optimum phenolics extraction conditions for PKC suggested in this study are by using water with 1:10 material to solvent ratio, stirring at 250 rpm, 25°C for 30 minutes. The ultra-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) analysis showed that p-hydroxybenzoic and protocetechuic acids were the predominant phenolics in methanol extract. Meanwhile, p-hydroxybenzoic, protocatechuic as well as shikimic acids appeared to be the predominant phenolics in water extract.

Keywords: Palm kernel cake (PKC), phenolic extraction, free soluble phenolics, bound phenolics