Abstract

Pectin was extracted from pumpkin (Cucurbita maxima) pulp at 82°C and pH 4.6, in the presence of ammonium oxalate at 0.25%. Soluble pectin was recovered as pectinates aluminium by precipitation, in the presence of aluminium sulphate. Extracted pectin contains uronic acids and neutral sugar with a percentage of 58.43±0.10% and 21.11% respectively. The studied pectin was highly methylated (DE 77.61±0.04%). Three equations were used: Huggins, Kraemer and Solomon, Cituâ and Morris to measure the intrinsic viscosity. The latter ranged from 9.00±0.40 to 10.86±0.60 dl/g. Its molecular weight depends on the intrinsic viscosity of pectin solution, as expressed by Mark-Houwink-Sakurada equation. The obtained values varied between 224.40±9.50 KDa and 266.64±20.34 KDa. The effect of pH on rheological behavior of pectin solution was investigated. At pH 4, pectin showed a non-Newtonian rheological behavior at low viscosities. The increase of pectin concentration led to the increases in viscosity and the rheological behavior becomes rheo-thickening. At pH 7, the viscosity of pectin solution was rather low to develop a non-Newtonian behavior or modify the Newtonian behaviour.The viscoelastic behavior of pectin studied at different concentrations. Solid behavior can be observed for relatively low values of G '(of a few Pa), indicating the existence of a three-dimensional structure.

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