A hydrodynamic study of the depolymerisation of a high methoxy pectin at elevated temperatures

The hydrodynamic properties (intrinsic viscosity, [eta]; infinite dilution sedimentation coefficient, s(20,w)(0); weight average molecular weight, M-w and translational frictional ratio,f/f(0)) of a high methoxy pectin have been evaluated at various temperatures (20-60degreesC). A reduction in the value of all four hydrodynamic parameters is indicative of depolymerisation and is in agreement with an earlier study using viscometry [Axelos, M.A.V., & Branger, M., (1993). Food Hydrocolloids, 7, 91-102]. The apparent linearity of the Mark - Houwink plot of log[eta] vs log M-w suggests that the conformation of the pectin molecule does not change significantly over the temperature range studied. The evaluation of the Mark-Houwink viscosity exponent (a = 0.84) indicates a moderately extended structure. This then allows the calculation of the number of Kuhn statistical lengths per chain from the adapted 'blob' theory of Dondos [Dondos A. (2001). Polymer, 42,897-901]. The weight average number of Kuhn statistical lengths per chain is reduced from (170 +/- 10) to (125 +/- 10) when the temperature is increased from 20-60degreesC. This may be of significance as many high methoxy pectins are exposed to high temperatures during processing in both the food and pharmaceutical industries. (C) 2002 Elsevier Science Ltd. All rights reserved.