Abstract: Purple potato was used as the raw material to extract pigment by microwave and ultrasonic methods. Both methods were compared and optimal extraction parameters of both methods were also explored. The results showed that the optimal microwave extraction conditions were using a 10-fold volume of a mixture of HCl and C2H5OH at a ratio of 50:50 as the extraction solvent to extract the raw material for 12 min at 75 ℃ in a microwave field. The optimal solvent composition for  ultrasonic extraction consisted of HCl and C2H5OH at a ratio of 40:60, and material/liquid ratio of 1:30 (g/mL), ultrasonic treatment time of 30 min and extraction temperature of 60 ℃. Microwave extraction derived purple sweet potato pigment had higher hydroxyl free radical scavenging capacity than purple sweet potato pigment obtained by ultrasonic extraction. Overall, microwave extraction is superior to ultrasonic extraction.

Key words: purple sweet potato pigment, microwave extraction, ultrasonic extraction, orthogonal array design, hydroxyl free radical