Physical and water sorption properties of chemically modified pectin with an environmentally friendly process.

A synthetic process was developed to modify pectin samples under solvent free conditions, obtaining pectin at increasing concentration of palmitic, oleic, and linoleic acids. The weight loss of the modified powders showed a degradation path very similar to the pure pectin, indicating that the pristine structure was preserved after the chemical modification. A decreasing mass of evaporating water on increasing the fatty acid concentration, in particular for the palmitic acid modification, indicated a reduced water sorption by the modified powders. Differential scanning calorimetry confirmed the thermogravimetric results and in addition indicated the crystallization of the lateral chains in the case of palmitic-acid-modified pectins. This result was confirmed by X-ray diffractograms of the palmitic acid samples, indicating the main crystallization of the form C, although possible orientation phenomena can be inferred. The sorption curves of either the pristine pectin or the modified samples showed a dual sorption behavior. The sorption curves were interpreted by the BET and GAB equations, both giving very similar results. Palmitic acid modification was very effective in reducing all sorption parameters, whereas in the case of oleic and linoleic acids, only at high concentrations was the hydrophobic influence detected.