Structural characteristics of pumpkin pectin extracted by microwave heating

To improve extraction yield of pumpkin pectin, microwave heating was adopted in this study. Using traditional hot acid extraction, pumpkin pectin yield decreased from 5.7 to 1.0 % as pH increased from pH 1.0 to 2.0. At pH 2.5, no pectin was recovered from pumpkin flesh powder. After a pre-treatment at pH 1.0 and 25 degrees C for 1 hr, pumpkin powder was extracted with flash microwaving at 120 degrees C for 3 min resulting in 10.5 % pectin yield. However, pre-microwaving at 60 degrees C for 20 min, did not improve extraction yield of pectin. When microwave heating at 80 degrees C for 10 min was applied after pre-microwaving, the final pectin yield increased to 11.3 %. When pH was adjusted to 2.0, the yield dropped to 7.7 % under the same extraction conditions. Molecular shape and properties as well as chemical composition of pumpkin pectin were significantly affected depending on extraction methods. Galacturonic acid content (51-58 %) of pumpkin pectin was lower than that detected in commercial pectin, while higher contents of neutral sugars and acetyl esters existed in pumpkin pectin structure. Molecular weight (Mw) and intrinsic viscosity ([nw]) determined for microwave-extracted pumpkin pectins were substantially lower than acid-extracted pectin, whereas polydispersity was greater. However, microwave-extracted pectin at pH 2.0 had more than 5 times greater Mw than did the pectin extracted at pH1.0. The [nw] of microwave-extracted pectin produced at pH 2.0 was almost twice that of other microwave-extracted pectins, which was comparable to that of acid-extracted pectin. These results indicate that extraction yield of pumpkin pectin would be improved by the flash microwave method and different pectin structure and properties can be obtained compared to acid extraction.