STUDY OF THE INFLUENCE OF IONIC STRENGTH AND pH OF THE SUSPENDING MEDIUM ON THE SIZE OF WHEAT STARCH GRANULES, MEASURED BY SEDIMENTATION/STERIC FIELDFLOW FRACTIONATION

摘要

The sedimentation/steric field-flow fractionation (Sd/StFFF) technique has been approved as a simple and accurate method for the size separation and characterization of starch granules. In the present work, we further investigate this application by studying the influence of the ionic strength and the pH of the suspending medium on the size of the wheat starch granules measured by Sd/StFFF.A bimodal size distribution curve was found by Sd/StFFF for the starch granules, in accordance with the results obtained by scanning electron microscopy (SEM). The number and weight average diameters for the large (A-type) and small (B-type) starch granules are independent of the presence of the indifferent electrolyte KNO_3 in the suspending medium, indicating that disintegration or aggregation phenomena of the starch particles are absent. The later was also verified by SEM. The fact that the suspension pH does not influence the number and weight average diameters of the starch granules is discussed, in relation to the zeta potentials of the particles, which were measured by a microelectrophoresis apparatus.