Peculiarities of sorption properties formation for pectin substances from different species of pumpkin

The investigation results of pectin substances isolated from the pumpkin species Cucurbita maxima (the varieties: Prikornevaya, Mramornaya, Volzhskayaseraya 92), Cucurbitamoschata (the varieties: Prikubanskaya 1, Vitaminnaya, Muskatnaya) and Cucurbitapepo (Staroselskaya variety) at the maturation time and during storage with 30 days’ intervals and carefully purified for sorption properties in relation to Pb2+-cations as model polyvalent ions are shown.Complexing ability for each specimen was determined by the complexometric titration method. Analytical characteristics (uronic component, the count of free carboxyl groups, amide component, the count of the carboxyl groups esterified with methanol and acetyl component) were determined by conductometric titration. Physicochemical parameter (pH of 1 % aqueous solution) was determined potentiometrically. The absence of obvious correlation between the proportion of free carboxyl groups and a complex-forming ability of pectin samples has been established experimentally. Also found no significant influence of amide component on that correlation. Based on the existing notions of charge formation mechanisms the generalized mathematical model of charge pectin molecules in aqueous solutions has been proposed. Analysis of this model solution has shown a high probability of pectic substances hydroxyl groups’ participation in sorption processes. It is also found that the proportion of adsorbed cations are not accounted direct interaction with primary and secondary functional groups for the test samples ranged from 59.6 to 98.2 % of the magnitude of their complexing ability. Based on simulation results it was suggested that sorption ability of pectin may be presented as a assuming of three components -polyvalent cations chemisorption by primary functional groups, cation adsorption due to the partial charge formed on the surface of the colloidal particles by the dissociation of hydroxyl groups as well as absorption due to part of the initial cation-containing aqueous solution “entrapped” in cells structured sediment. It should be mandatory to take into account when determining the requirements for analytical and physicochemical properties of pectin, when used them as a component of a prescription for the creation of functional’ and special purpose’ foods.