Sequential extraction of bioactive compounds from tangerine (Citrus Unshiu) peel

Tangerine (Citrus Unshiu) is one of important agricultural crops in Georgia. As the statistical data for year 2016 manifest, the total harvest exceeds 100 thousand tons. Tangerine peel, agro-industrial waste of production of juice concentrates and jams present rich sources of valuable bioactive compounds. Due to their high bioactive compound content, tangerine peels could be applied by both pharmaceutical and food industries. In spite of this, citrus peel is usually treated as by-products or waste, resulting in environmental pollution. Citrus peels are promising source of essential oil, carotenes, natural flavanones such as hesperidin and pectin. Stepwise, sequential utilization of tangerine peel, which provides an opportunity for selective extraction of the aforementioned bioactive compounds and allows one to manage nonstandard tangerine (amounting to a third of the harvest) in a rational manner. Hence, the present study is undertaken to elaborate a feasible and effective method of sequential extraction of above mentioned bioactive compounds from tangerine peel. The first step is supercritical CO₂ extraction of essential oil. Optimal conditions for β-carotene free tangerine oil are 100 atm pressure, 35C⁰ temperature, and 15 min equilibrium time. The principal compound in Citrus Unshiu peel essential oil is d-limonene. Stepwise extraction requares correct extraction sequence of target products. Acetone (7%) was used as co-solvent in the second step of extraction. The β-carotene is soluble in acetone, whereas hesperidin is not. Optimal parameters are 150 atm, 40 °C and 1 h equilibrium, and 1 h extraction time in dynamic conditions. Methanol (7%) was used in the third step of extraction. Optimal parameters were: 250 atm pressure, 60 °C temperature, 1 h equilibrium and 30 min dynamic extraction time. At least pectin was extracted from residue of tangerin. Stepwise supercritical fluid extraction of bioactive compounds from agro-industrial waste materials is simple, effective, eco friendly separation method, which provides high quality of target products and needs one standard technological equipment.