Abstract: Chemical surface gelatinization (CSG) technique was employed to unravel uncover the location of acylation and hydroxypropylation groups in wheat starch granules and the change of molecular mass of wheat starch. Granule properties, molecular mass and substitution group distribution were determined using scanning electron microscopy and gel permeation chromatography. The results indicated that: as theincrease in degree of surface gelatinization increased, the particle surface became rough and showed obvious peeling; the remaining part was still in the granular state. The total carbohydrate content and blue value were decreased after CSG and the remaining granules showed a decreased amylose content. The substitution degree of the remaining granules of mono and dual modified starches decreased with increasing duration of CSG treatment. The higher the gelatinization degree of the outer layer, the lower the degree of substitution of the remaining granules indicating that acetylation and hydroxypropylation modifications occur mainly in the outer part of the granule and the substitution groups primarily exist on the surface of both modified starch granules.

Key words: wheat starch, surface gelatinization, substitution groups, dual-modification, molecular mass distribution