Ultrasonic-assisted extraction of anthraquinones from Heterophyllaea pustulata Hook f. (Rubiaceae) using ethanol–water mixtures

• UAE is an attractive alternative to the extraction of natural AQs.
• The optimization technique based on Taguchi minimizes the number of trials, time, and experimental costs,
• Optimal conditions were: 60:40 (v:v) ethanol/water solvent composition, a solvent/sample ratio equal to 20:1, a temperature of 55 °C, and an extraction time of 30 min.

In this study, ultrasound-assisted extraction (UAE) was evaluated as an easier and more efficient alternative method for the isolation of anthraquinones (AQs) from Heterophyllaea pustulata Hook f. (Rubiaceae), compared with conventional extraction techniques. The extraction was performed using an ethanol–water solution as solvent. The influence of different operating conditions, as temperature, time, solvent composition, and solvent/sample ratio and its relationship with ultrasonic techniques was analyzed. For this purpose and to achieve global optimization of the ultrasound-assisted extraction of H. pustulata, Taguchi experimental design with a L9 orthogonal array was applied.The results showed that the yield obtained with the ultrasound assisted extraction is approximately twice higher than the traditional Soxhlet technique, and Taguchi analysis demonstrated that the most influential factor is solvent concentration, followed by time, temperature, and solvent/sample ratio. The solvent composition effect is directly related to cavitation process, and the effect of solvent physical properties on it. The optimal combination of these factors on the ultrasound assisted extraction is a solvent composition 60% v/v of ethanol, a solvent/sample ratio equal to 20:1, a temperature of 55 °C, and an extraction time of 30 min.