Characterisation of dragon fruit peel pectin extracted with natural deep eutectic solvent and sequential microwave-ultrasound-assisted approach

In this research, the physicochemical characteristics (proximate and chemical compositions, monosaccharides profiles, chemical structures, antioxidant activities and rheological properties) of dragon fruit peel pectin extracted with the solvent system of choline chloride-glucose-water (5:2:5) and sequential microwave-ultrasound-assisted approach (PC-MUAE), were evaluated, and then compared with those of the commercial pectin and other products from various extraction methods. No remarkable differences in the FTIR spectra of the commercial and extracted samples were observed, leading to the fact that the derived polysaccharides were pectin. The commercial pectin possessed a bright-yellow colour, while extracted pectin was yellow to brownish. Moreover, the facade of the latter under SEM was rough with miniature heterogeneous fragments. PC-MUAE was categorised as high methoxyl pectin with the degree of esterification of 59.76% and as a pseudoplastic substance with neutral pH (6.42), average level of solubility (73.90%), high equivalent weight (680.6 g mol−1), high molecular weight (5.05 × 105 Da), high antioxidant activities (total phenolic content of 8.14 mg of gallic acid equivalent/g pectin and 2,2-Diphenyl-1-picrylhydrazyl free radical scavenging capacity of 2.41 µmol Trolox equivalent/g pectin) and high viscosity at all tested domains of shear rate as compared with those of the commercial product and others from various methods. The anhydrouronic acid content of PC-MUAE was 64.28%, approximately to the minimum level (65%) proposed by FAO and EU. There were arabinose, galactose, glucose, mannose, rhamnose and xylose detected in extracted pectin. Consequently, PC-MUAE has the potential characteristics of high methoxyl pectin for the food industries.