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

The hydrodynamic properties (intrinsic viscosity, [ η]; 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 (20–60°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 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 20–60°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.