Evaluation of green extraction methods on the chemical and nutritional aspects of roselle seed (Hibiscus sabdariffa L.) oil

Roselle is one of the valuable plants grown in some regions of Egypt, which is used to make juices or as natural food color additive. Roselle seeds are waste, which can be used as a source of nontraditional oil, nutritious or functional compound. The evaluation of green extraction methods including supercritical CO2 (SC-CO2), screw, hydraulic press comparing to traditional method on oil yield, total phenolics, antioxidant activity (DPPH) and oxidative stability of roselle seeds oil were investigated. Fatty acid composition and tocopherol of the oil were also determined. The results showed that the roselle seeds oil extracted by solvent gave the highest oil content and extraction rate (17.98 and 98.34%, respectively) and the lowest peroxide and acid value. SC-CO2 gave the higher content of alpha, gamma, and delta tocopherol comparing to the other extraction methods. Fatty acid showed that linoleic acid, an essential fatty acid, was dominant followed by oleic and palmitic acids. These fatty acids were higher amounts in oil extracted by SC-CO2, followed by cold-press comparing to solvent extraction. The maximum stability (20 h), higher TPC (22.18 mg GAE/g) and antioxidant activity (DPPH, 65.15) were observed in oil extracted by SC-CO2 followed by hydraulic-press, solvent extraction and finally screw-press. The results revealed that SC-CO2 method is more efficient in determination of total tocopherol, oxidative stability, TPC and radical scavenging activity than the other extraction methods. Cold press extraction methods gave higher oil yield than SC-CO2 and more economically than other methods.