The present study reports on the extraction of natural pigment from annatto seeds. Response surface methodology (RSM) was used to investigate the effect of process variables on the ultrasound-assisted extraction (UAE). Four independent variables including temperature (20–80 C), sonication time (2–10 min), duty cycle (0.2–0.8 s) and the ratio of seeds to the solvent (5–20%) were studied. According to the results, the optimal UAE condition was obtained with a temperature of 72.7 C, extraction time of 7.25 min, the ratio of seed to solvent of 14% and duty cycle of 0.8 s. At these conditions, extraction yield determined as 6.35% and the absorbance value as 0.865%. The experimental values under optimal condition were in good consistent with the predicted values, which suggested UAE is more efficient process as compared to conventional extraction.

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