Pectin adsorption onto and penetration into starch granules and the effect on the gelatinization process and rheological properties

Abstract

Adsorption isotherms have been determined to investigate the nature of the interaction between pectin molecules and rice, potato and pea starch granules. The amount of pectin adsorbed was found to be very much higher for potato and pea starches (∼50 mg/m2) compared to rice starch (∼5 mg/m2). This indicated that a significant amount of pectin penetrated into the interior of the granules through the surface pores and channels for potato and pea starch, while for rice starch the penetration was much less and most of the pectin may be accommodated on the granule surface. The adsorption/absorption of pectin molecules significantly reduced the amount of amylose leaching out of the granules at room temperature in excess water suggesting that the granule channels and pores were blocked by the pectin. The adsorption/absorption also led to a reduction in the swelling of the granules on heating and to a slight increase in the gelatinization temperatures and enthalpies. The pectin had a significant influence on the viscosity profile of starch dispersions on heating and cooling under shear. This has been attributed on initial heating to the adsorbed/absorbed pectin molecules influencing the gelatinization process by reducing granule swelling and then following gelatinization on cooling to thermodynamic incompatibility of starch and pectin molecules in solution and their tendency to segregate.