Abstract: From commercially available apple pectin, pH-modified and heat-modified pectin were prepared through pH modification and high-pressure steam treatment, respectively. The physical and chemical properties of native and modified apple pectin were investigated, and further, their antioxidant activity was examined. The results showed that galacturonic acid contents of pH-modified and heat-modified pectin increased from (683.92 ± 4.51) mg/g to (910.61 ± 1.08) and (780.19 ± 5.68) mg/g, respectively, and the degree of esterification was reduced from (77.26 ± 1.20)% to (35.48 ± 1.90)% and (33.67 ± 1.28)%, respectively as compared to the native one. The molecular weight of pectin reduced and the contents of polyphenol and protein were reduced (to less than 3 and 7 mg/g, respectively) after modification. The scavenging activity of all three apple pectins against 1,1-diphenyl-2-picrylhydrazyl, hydroxyl, 2,2’-azino-bis-(3-ethylbenzothiazoline- 6-sulfonic acid) diammonium salt and superoxide anion free radicals was enhanced with their increasing concentration, and pH modification could contribute to improving the antioxidant activity of pectin, which may be related to its increased galacturonic acid content.

Key words: modification, apple pectin, pectin characterization, antioxidant activity