Effects of ultrasound-assisted extraction conditions on the recovery of phenolic compounds and in vitro antioxidant activity of jujube (Ziziphus jujuba mill.) leaves

Abstract

The optimum conditions for the Ultrasound-Assisted Extraction (UAE) of total phenolics and antioxidant activity from jujube leaves were studied. The effect of the solvent nature (acetone, methanol, ethanol and water), solvent concentration (25-100%; v/v), ultrasound intensity (25-100%), solid/solvent ratio (1/50-1/300; w/v) and extraction time (1-15 min) were also determined. The total phenolic content was used to determine the phenolic compounds. Ferric-reducing power and 2,2-diphenyl-1-picrylhydrazyl (DPPH) were used to evaluate the antioxidant activity. All the ultrasound-assisted extraction parameters that were investigated had from a statistically point of view significant effects (p<0.05) upon the phenolic compound extraction and antioxidant activity. The best extraction conditions were obtained by using methanol 60 %, a sonication intensity of 75 %with a solid/solvent ratio of 1/200(w/v), for 10 min. As such, the obtained values were 6.0g gallic acid equivalents/100g for total phenolic content, 3.886 g ascorbic acid equivalents/100g for free radical scavenging activity and 2.587 g ascorbic acid equivalents/100g for ferric reducing power. The phenolic content was positively correlated with the antioxidant activities.