The interaction of pectin with wheat starch and its influence on gelatinization and rheology

Adsorption isotherms have been determined for pectin obtained from citrus peel, apple pomace and creeping fig seeds onto wheat starch granules at room temperature. The results show that the amount adsorbed was significantly higher than can be accommodated solely on the surface of the granules and is, therefore, evidence that the pectin molecules must penetrate into the interior of the granules through the surface pores. The amount of pectin adsorbing/absorbing into the granules was found to decrease with increasing pectin molar mass. The adsorption/interpenetration of the pectin molecules reduced the amount of starch molecules leaching from the starch granules at room temperature. The transition temperatures and enthalpy of the gelatinization process were determined by differential scanning calorimetry and found to slightly increase in the presence of the pectin samples and with the degree of pectin interpenetration. The viscosity of starch – pectin dispersions on heating and cooling under constant shear increased with increasing pectin concentration. The final viscosity values of the starch pastes decreased with increasing pectin molar mass. The study provides a clearer understanding of the nature of starch–pectin interactions which will be of significant importance in food formulation.