Abstract: This study was implemented to investigate the effect of heat treatment under acidic condition on the rheological and structural characteristics of pectin and to unravel the underlying mechanism. After heat treatment under acidic condition, changes in the apparent viscosity and rheological properties of high-molecular-mass pectin from pomelo peel were examined as well as changes in some physicochemical measurements such as galacturonic acid content, degree of esterification and molecular mass distribution. We also investigated the structural changes of the pectin molecule using an atomic force microscope (AFM). The results obtained showed that the apparent viscosity and consistency coefficient of the pectin declined significantly during 0–100 min of heat treatment at 85 ℃ and pH 3.7 (P < 0.05), while the flow behavior index n increased significantly (P < 0.05). Nonetheless, there was no significant change in galacturonic acid content, degree of esterification or molecular mass distribution (P > 0.05). Moreover, the pectin molecule was changed from a dispersive and unfolded state to an aggregate state, altering the spatial structure and consequently the apparent viscosity and rheological properties and attenuating the thickening effect of the pectin.

Key words: pectin, heating treatment, rheological characteristic, molecular mass distribution, molecular structure