A novel technology for extraction of phenolic antioxidants from mandarin (Citrus deliciosa Tenore) leaves: Solvent-free microwave extraction

Abstract

Solvent-free microwave extraction (SFME) of polyphenols and flavonoids from mandarin (Citrus deliciosa Tenore) leaves was investigated. A face central composite design (FCCD) through response surface methodology (RSM) was applied to study the effects of extraction time (30-90 sec), microwave irradiation power (250-350 W) and solid mass (2.5-7.5 g), and to optimize the extraction process. The optimum conditions were: extraction time, 53.155 sec; microwave power, 339.190W; and solid mass, 2.500 g. Under the optimum conditions, 0.8610mg-GAE/g-DL of total phenolic content (TPC) and 0.2440mg-CE/g-DL of total flavonoid content (TFC) were extracted. The antioxidant activity of the extracts was assessed by cupric ion reducing antioxidant capacity (CUPRAC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) methods, respectively. Antioxidant values were expressed as mg trolox equivalent antioxidant capacity per gram of dried leaf (mg-TEAC/g-DL). CUPRAC values were highly correlated with both TPC and TFC (r=0.9282/0.8842, P=0.05) in the extracts, whilst DPPH (r=0.7717/0.7435, P=0.05) and ABTS (r=0.6814/0.7072, P=0.05) were relatively less correlated with the same responses.