Abstract: Using citrus pectin as raw material, the process conditions for preparing modified citrus pectin using ultrasonic and microwave assisted pectinase were studied, and the physicochemical properties and structural characteristics of modified and original citrus pectin were characterized by liquid chromatography, Fourier infrared spectroscopy and scanning electron microscopy. The results showed that the degradation efficiency of pectinase could be improved by both ultrasonic and microwave treatment. The weight average molecular weight of the pectin obtained by several degradation methods was 56.18% which was lower than that of the original pectin (283 kDa). Ultrasonic and microwave effect can significantly increase the content of galacturonic acid(GalA), microwave processing enzyme substrates (MEP Ⅰ), microwave digestion product (MEP Ⅱ), ultrasonic treatment enzyme substrates (UEP Ⅰ), ultrasonic treatment enzymolysis products (UEP Ⅱ) GalA content than pectin enzyme solution (39.57%) increased by 52.31%, 46.88%, 66.69% and 61.11% respectively. Moreover, different degradation methods did not change the monosaccharide types of pectin, but made the composition of monosaccharides different. At the same time, it was found that the main chain and side chain of pectin were broken to different degrees after modification, and the degree of esterification was reduced. Scanning electron microscopy (SEM) showed that pectinase, microwave and ultrasound changed the microstructure of pectin in different degrees.
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