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.