Optimization of heat- and ultrasound-assisted extraction of polyphenols from dried rosemary leaves using response surface methodology

Practical applications The conditions used in heat- and ultrasound-assisted extraction (HAE and UAE, respectively) of polyphenols from rosemary leaves were optimized using response surface methodology. The optimum HAE conditions included an extraction time of 132.80 min, temperature of 70 degrees C, and 20:1 liquid-to-solid ratio, resulting in the maximum total extraction yield (TEY, 17.80%) or total polyphenol content (TPC, 147.56 mg GAE/g of extract DW), and minimum IC50 (994.68 mu g/ml); the maximum TEY (20.82%) or TPC (185.16 mg GAE/g of extract DW), and minimum IC50 (805.84 mu g/ml) in the UAE process were obtained using optimum conditions, including time of 12.60 min, power of 200 W, and ethanol concentration of 56.26%. The lowest IC50 (787.70 mu g/ml) was recorded using a solvent mixture of water and ethanol (56%) in the HAE procedure similar to the amount determined for the BHT antioxidant (714.79 mu g/ml), thus confirming the efficiency of the extraction procedure. The antioxidant properties of rosemary leaves are well characterized; hence, this plant's extract is approved as the only accepted natural food antioxidant in the EU. Generally, the extraction of active compounds from rosemary leaves is performed by the HAE method. However, it is recommended to use sustainable technologies, such as UAE. The optimization of both conventional and UAE of polyphenols from rosemary leaves has not been studied in the literature. Therefore, the purpose of the present study was to introduce the optimal conditions of the HAE and UAE methods required to obtain maximum extraction efficiency of polyphenol compounds from rosemary leaves, and then was to compare possible procedures so that a comprehensive method to be developed.