Abstract:
In the present work, phenolic compounds were extracted from Vernonia amygdalina leaf by ultrasonic assisted extraction method. Effect of ethanol concentration on the extraction was studied and the results showed that the highest phenolic (84.05 ± 2.33 mg GAE/g extract) was significantly obtained by 80 % w/v ethanol, whereas use of absolute ethanol provided the highest flavonoid content (459.49 ± 3.70 mg QE/g extract). Antioxidant capacity assayed by DPPH radical scavenging activity and ferric reducing antioxidant power (FRAP) were greatly obtained at 87.15 ± 1.60 and 121.68 ± 2.43 mg TEAC/g extract, respectively when 80 % ethanol was employed. Response surface methodology (RSM) based on Box Behnken design (BBD) was used to optimize the extraction conditions of phenolic antioxidant compounds from Vernonia amygdalina leaf. Three independent variables including solvent-to-solid ratio, ethanol concentration and extraction time were investigated via parameters of extractable phenolic compound, flavonoid content, DPPH radical scavenging activity and ferric reducing antioxidant power (FRAP). The results revealed that the all factors had significant effect on the all responses (P < 0.05). The optimum extraction conditions determined from 3D response surface were solvent-to-solid ratio of 28.07 % v/w, ethanol concentration of 81.36 % v/v and extraction time of 25.17 min from the predicted conditions, it could provide the predicted values of 89.15 mg GAE/g extract, 213.46 mg QE/g extract, 100.92 mg TEAC/g extract and 134.53 mg TEAC/g extract for phenolic content, flavonoid content, DPPH radical scavenging activity and FRAP, respectively. The optimum conditions could be further applied for production of Vernonia amygdalina extracts in cosmetic industry.