Recovery of bioactive compounds from oil palm waste using green extraction techniques and its applications

Oil palm (Elaeis guineensis) is a major oil crop that significantly contributes to the Indonesia's and Malaysia's economic growth. However, oil palm processing for oil extraction generates substantial waste, such as palm kernel cake, palm-pressed fibre, oil palm empty fruit bunches and palm oil mill effluent, which pose noticeable environmental challenges. This review explores green extraction techniques for palm waste processing, which include microwave-assisted extraction, deep eutectic solvents, ultrasound-assisted extraction, supercritical fluid extraction, enzyme-assisted extraction and subcritical water extraction. The potential for industry scaling, mechanisms, applications and challenges of each technique used for oil palm waste are discussed. Microwave-assisted extraction, ultrasound-assisted extraction and supercritical fluid extraction are particularly promising for large-scale production, while deep eutectic solvents paired with ultrasound-assisted extraction show the potential to improve extraction efficiency. This review also reveals that green extraction techniques are sustainable alternative to conventional techniques by effectively recovering valuable compounds from waste with reduced environmental impact. Additionally, the diverse applications of bioactive compounds (vitamin E, phytosterols, phenolics, polyphenols and flavonoids) extracted from oil palm waste in food, pharmaceutical, cosmetic and other industries are also presented. Valuable components such as cellulose, dietary fibres and bioactive peptides derived from the waste can be applied in food coatings, high-protein products and drug delivery systems. Biosorbents, biofuels and biodegradable products derived from the waste would also provide environmental benefits. Future research should focus on optimising the green extraction techniques for industrial use to promote responsible production and circular waste management to foster health and environmental safety.