Extraction of Pectin from Satsuma Mandarin Orange Peels by Combining Pressurized Carbon Dioxide and Deionized Water: a Green Chemistry Method

Pectic oligosaccharides have vital properties that are dependent on their molecular assemblies, such as the degree of esterification (DE) and branched side chains. The molecular structures are affected by the extraction solvents and conditions. In this study, we used pressurized carbon dioxide treatment (CT) as a novel method for pectin extraction from fresh and ripe orange peels and compared the total yield, DE, molecular weight, and monosaccharide compositions of the product obtained with those of products obtained using conventional extraction methods, such as heating with HCl or chelating with sodium hexametaphosphate (SHMP). CT provided a yield of approximately 3.8%, which was less than that of HCl (9.9%/dry weight). However, DE in the CT extract was approximately 94%, which was higher than that of HCl (75%) and SHMP (59%). The molecular weights of pectins in the CT extract appeared to be higher than that of HCl, except at a pressure of 2 MPa. β-Galacturonic acid was the major monosaccharide in pectin extracted by HCl and SHMP, whereas that was decreased in CT extract from fresh oranges. The results showed that extraction with CT contributed to a high DE pectin yield and diverse pectin molecular structures compared to conventional methods, although its application resulted in a lower overall pectin yield. These findings suggest the possibility of manufacturing oligosaccharides with novel properties.