Rheological behavior and electrokinetic properties of pectin extracted from pumpkin (Cucurbita maxima) pulp and peel using hydrochloric acid solution

Abstract

The aim of this study is to investigate the chemical composition, hydrodynamic, rheological, and electrokinetic properties of pectin extracted from pulp and peel of pumpkin “Cucurbita maxima” by hydrochloric acid solution at pH 1.8. Chemical analysis of the extracted pectin showed an abundance of galacturonic acid which represents the totality of the uronic acid. Its content in the pulp and peel pectin extracts was 52.91 ± 0.02 g/100 g and 55.14 ± 0.10 g/100 g of dried samples, respectively. The results for intrinsic viscosity [η] ranged from 5.13 ± 0.04 to 5.65 ± 0.08 dl/g and for molecular weight from 234.64 ± 2.33 to 267.40 ± 5.39 kDa. These macromolecules are semi-flexible chain biopolymers with flexibility values of 0.07 ± 0.00. The parameter measurement of the pectin such as hydrodynamic radius (Rh) ranged from 32.39 ± 0.19 to 34.93 ± 0.40 nm, the relaxation time (tr) from 2.77 ± 0.02 × 10−7 to 11.26 ± 0.00 × 10−7 ms, and the diffusivity coefficient (D) from 2.17 ± 0.00 to 8.73 ± 0.00 cm2/s. The rheological behavior was suitably represented by the Bingham and Herschel–Bulkley models for all concentrations. The electrokinetic behavior of pectins allows control of electrostatic interactions. The calculated Zp of the system constituted by pumpkin pectin and citric acid/sodium citrate buffer ranged from − 28.10 ± 0.20 to + 0.35 ± 0.65 mV.