Morphological, thermal and rheological properties of starches from different botanical sources

Corn, rice, wheat and potato are the main sources of starches which differ significantly in composition, morphology, thermal, rheological and retrogradation properties. Cereal starches contain a significant quantity of phospholipids, while potato starch is rich in esterified phosphorus. Potato starch exhibits higher swelling power, solubility, paste clarity and viscosity than wheat, rice or corn starches. Morphological characteristics, such as shape and size of the starch granules, exhibit significant differences. Potato starch granules are smooth-surfaced, oval and irregular or cuboidal-shaped while corn, rice and wheat starch granules are angular, pentagonal and angular; and spherical and lenticular-shaped, respectively. Corn, rice and wheat starch granules are less smooth-surfaced than potato starch granules. Potato starch granules are largest (< 110 mu m) in size followed by wheat (<30 mum), corn (<25 mu m) and rice (<20 mum) starches. Gelatinization temperatures (T-o, T-p, T-c) and enthalpies of gelatinization (DeltaH(gel)) of starches from different sources also differ significantly. Corn and rice starches generally show higher transition temperatures than wheat and potato starches while the DeltaH(gel) values are higher for potato and wheat starches. Potato starch shows a higher tendency towards retrogradation than the cereal starches. The rheological properties, such as storage modulus (G') and loss modulus (G") of the starches from the different sources increase to a maximum and then drop during heating of all the starches. Potato starch shows highest peak G', G" and lower tan delta than corn, rice and wheat starches during the heating cycle. (C) 2002 Elsevier Science Ltd. All rights reserved.