Effect of temperature and concentration on viscosity of orange peel pectinsolutions and intrinsic viscosity-molecular weight relationship

The effects of temperature and concentration on the viscosity of orange pee l pectin solutions were examined at five different temperatures between 20 and 60 degrees C and five concentration levels between 2.5-20 kg/m(3). The effects of temperature was described by an Arrhenius-type equation. The act ivation energy for viscous how was in the range 19.53-27.16 kJ/mol, dependi ng on the concentration. The effect of concentration was described by two t ypes of equation, power-law and exponential. Equations were derived which d escribes the combined effects of temperature and concentration on the visco sity for two different models in the range of temperatures and concentratio ns studied. Orange peel pectin was extracted by using HCl (pH 2.5, 90 degre es C, 90 min) ammonium oxalate (0.25%, pH 3.5, 75 degrees C, 90 min) and ED TA (0.5%, 90 degrees C, 90 min) extraction procedures. The best result was obtained with ammonium oxalate extraction in which the pectin content of th e final product was 30.12%, although the efficiency among the procedures va ried. The average molecular weight was measured by light scattering techniq ue. Magnitudes of intrinsic viscosity and molecular weight of pectins obtai ned by extraction with HCl, ammonium oxalate and EDTA were 0.262, 0.281, 0. 309 m(3)/kg and 84 500, 91 400, 102 800 kg/kgmol, respectively. The molecul ar weight dependence of the intrinsic viscosity of the orange peel pectin s olutions was expressed by Mark-Houwink-Sakurada equation. The data were fin ed to equation as eta(i) = 2.34 X 10(-5) (M-w,M-ave)(0.8224) which helps to evaluate the average molecular weight of pectin solutions from orange peel with a knowledge of their intrinsic viscosity. (C) 1999 Elsevier Science L td. All rights reserved.