Experiment on dual-frequency ultrasound extraction of black rice melanin

To improve extraction rate of black rice melanin, dual-frequency ultrasound assisted extraction method of black rice melanin was used. Orthogonal array design was employed for investigating the effects of pH, extraction time, extraction temperature, liquid ratio, concentration of ethanol. The results showed that the impact of various factors on the black rice melanin extraction was followed by pH, concentration of ethanol, liquid ratio, extraction temperature, extraction time. The optimal conditions were as follow: pH value of 2, ultrasound time of 30 min, extraction temperature of 50°C, the liquid-solid ratio of 30mL/g, ethanol concentration of 70%. Under these conditions, average extraction rate was 6.85%. Compared to impregnation and ultrasound extraction methods, dual-frequency ultrasound assisted extraction method exhibited simple, saving time, less solvent, high extraction efficiency and less melanin.