Optimization of microwave-ultrasound- assisted extraction (MUAE) of pectin from dragon fruit peels using natural deep eutectic solvents (NADES)

The aim of this research is to define promising green techniques and natural deep eutectic solvents (NADESs) for pectin extraction from dragon fruit (Hylocereus polyrhizus) peels with the aid of the Box-Behnken design. Among all possible methods and solvents in this study, the highest pectin yield was recorded for microwave-ultrasound-assisted extraction (MUAE) using the solvent system of choline chloride–glucose– water (5:2:5). Under the optimized condition including liquid/solid ratio of
35.25 ml/g, water/NADES ratio of 3.37 ml/ml, microwave irradiation of 14.26 min at 240 W followed by sonication of 46.07 min, the pectin yield was 19.39%. The obtained product could be verified as high methoxyl pectin with the degree esterification of 50.77% and as a pseudoplastic substance with the flow behavior index of 0.14. As a result, a combination of MUAE and NADES on pectin extraction from dragon fruit peels can favor a higher yield with desirable quality.
Novelty impact statement:
The system of choline chloride-glucose-water can be used as an eco-friendly solvent for pectin extraction. The sequential employment of microwave and ultrasound could provide better efficiency than their individual techniques. The combination of screening and the Box-Behnken design could help deal with a large number of process variables, resulting in milder operation conditions with desirable product quality.