Preparation and characterization of pectin hydroxamates from citrus Unshiu peels

Abstract

Pectin was extracted from unshiu orange (Citrus unshiu) peels and was subjected to chemical modification using hydroxamic acid. The structural and physical properties of the resulting derivatives were investigated as a function of hydroxamic acid content (4.68-9.58%). The extracted unshiu orange pectin showed 66.8% degree of esterification, 787.5 mg/g galacturonic acid, and 92 mg/g neutral sugars, which were composed of arabinose (53%), galactose (35%), glucose (5%), rhamnose (5%), and fructose (2%). Compared to the native pectin, the FT-IR spectra of the hydroxamic acid derivatives showed two new absorption bands at 1,646 cm -1 (C=O) and 1,568 cm -1 (N-H). Specifically, the pectin derivatives with more hydroxamic acids were shown to have enhanced water solubility, upto two-fold higher than that of the native pectin. Thus, the introduction of hydroxamic acid into the pectin structure appears to be a useful tool for improving the solubility of pectin.