Soxhlet, microwave-assisted, and room temperature liquid extraction of oil and bioactive compounds from palm kernel cake using isopropanol as solvent

Abstract

In this study, the extraction of oil and bioactive compounds from palm kernel cake (PKC), a byproduct of the palm oil mill, was investigated using Soxhlet extraction (SE), microwave-assisted extraction (MAE), and room-temperature liquid extraction (RTLE) using isopropanol as a solvent. The advantages and disadvantages of each technique based on oil extraction yield, energy consumption, types and quantity of extracted bioactive compounds, and the characteristics of defatted PKC were compared. The results showed that when using an extraction temperature of 150 °C, SE provided the highest oil extraction yield of 12.64% w/w dry basis. When considering energy consumption, the RTLE required the lowest energy input of 0.14 kWh/g oil. The MAE yielded a comparable amount of extracted oil to that of SE (11.70%w/w dry basis), while requiring a moderate energy input of 1.52 kWh/g. Evidently, both the extraction method and solvent type influenced the fatty acid composition of the extracted oil. In addition to oil, the main compounds extracted from PKC using isopropanol were 3-pyridinol and 5-hydroxymethylfurfural. Aromatic and phenolic compounds, including benzoic acid, 5-hydroxymethylfurfural, and 3-pyridinol, were detected in the oil-soluble components only when isopropanol was employed as the solvent, and the extraction temperature was ≥ 120 °C. In addition, the results showed that the extraction of oil from PKC produced defatted PKC, which may have a longer storage time than the untreated PKC and that can be a potential source of dietary fiber and protein for human consumption.