Orange peel volatile oil: A green solvent for propolis extraction, enhanced α-amylase inhibition activity

Orange peel oil contains high amount of d-limonene which is reported to have antidiabetic activity. Propolis contains many biologically active compounds like phenolic acids, flavonoids and terpenes. Because of its rich phenolic composition, antidiabetic activity of propolis has also been shown in literature. Consumption of raw propolis is limited because of its resinous nature. It should be extracted to convert it into consumable form. Ethanol is the most used solvent for this purpose. Ethanol is the limiting factor for propolis consumption either for religious concerns or being harmful for human health. There is an increasing need for new, compatible and healthier solvents for propolis extraction. This is the first paper describing the extraction of propolis with orange peel oil. 1:10 (g/v) ratio was used for extraction. Orange peel oil (OPO), orange peel oil propolis extract (OPOPE) and ethanol propolis extract (EPE) were separately analysed by using GC-MS technique. Total phenolic content of oil and propolis extract was also carried out. Inhibition of alpha-amylase from barley malt with new extract was also reported. It was found that OPOPE was rich in volatile compounds of propolis, phenolic acid derivatives and free fatty acids. It was observed that OPOPE showed higher inhibition on alpha-amylase enzyme (IC50 0.196 mg/mL). It can be concluded that orange peel oil could be used as solvent for preparing propolis extract. Propolis extract obtained with orange peel oil could also be used as complementary medicine for the treatment of type 2 diabetes.