The concentration-modified physicochemical surface properties of sodium carbonate-soluble pectin from pears (Pyrus communis L.)

Abstract

Cross–linking and gelation are important abilities affecting pectin functionality. Pectin concentration, pH and the composition of the dispersing medium play a crucial role in gel formation. The self-assembly of pectin in solution occurs simultaneously with changes in its physicochemical properties. However, this process has not been described in detail to date. Therefore, the effect of pectin concentration on such properties as its surface electrical charge (Q), hydrogen ions binding (βH+) and total counterions binding (βtotal) during intermolecular interactions in different media was studied. Low–methoxyl diluted alkali–soluble pectin (DASP) extracted from pear fruits by using sodium carbonate was examined. Investigations were performed on a wide range of its content (1.84·10−4–1.84·100% w/v) in water and salt (NaCl and CaCl2) solutions with the ionic strength of 30 mM at 20 °C. Back Dynamic Light Scattering, Laser Doppler Electrophoresis, potentiometry and Atomic Force Microscopy methods were used. The DASP dissociation constant was calculated and used for determination of other physicochemical parameters. The relationship between changes in the physical and physicochemical properties of DASP during gelation was shown. An increase in the relative mean hydrodynamic diameter with DASP concentration was connected with the self–assembling (CaCl2) and cross–linking (water, NaCl) processes leading to gel formation. Simultaneously, the Q value decreased, βH+, βtotal and the contribution of βH+ to βtotal increased up to the obtained constant values at the gel state. Thus, the physicochemical properties of pectin may be indicators of the particular stages of macromolecules interactions occurring during gelation.