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

The hydrodynamic properties (intrinsic viscosity, [η]; infinite dilution sedimentation coefficient, s20,w0; weight average molecular weight, Mw and translational frictional ratio, f/f0) of a high methoxy pectin have been evaluated at various temperatures (20-60°C). 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[η] vs log Mw 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 20-60°C. This may be of significance as many high methoxy pectins are exposed to high temperatures during processing in both the food and pharmaceutical industries. © 2002 Elsevier Science Ltd. All rights reserved.