Microscopic and thermal characteristics of experimental models of starch, gliadins, glutenins and gluten from semolina

Durum wheat semolina is the preferred and most often used raw material for the production of dried pasta. The high quality of pasta is attributed to its specific structure, obtained after successive structural changes of the two main semolina components, starch and proteins, gliadins and glutenins, in presence of water. The present study was conducted to examine the contributions of gliadins, glutenins and starch to the structure and functionality of gluten by means of scanning electron microscopy (SEM) and of differential scanning calorimetry (DSC). Isolated samples of the main semolina components (starch, gliadins, glutenins) and gluten were considered. Experimental models were then prepared from defined binary mixtures of starch and proteins (gliadins or gluteins or gluten) and from respective doughs with water (50 % w/w). SEM of surface morphology provided stereoscopic images with high magnification. Semolina starch was composed of small spherical B-type granules (average diameter 2-3 μm) and larger lenticular A-type granules (average diameter 30 μm). The micrographs from starch - gliadins dough showed a distinct film surrounding the small and large starch granules. In the starch - glutenins doughs, most of the starch granules appeared naked, it seems that the proteins are unable to surround all of the starch gran ules. A possible explanation for this is that the lack of gliadins can be affecting the formation of the film structure in fact gliadins may be involved in the development of the structure of the gluten film networks through covalent and non-covalent bonding with other gluten proteins. DSC allowed the observatio n of all phenomena that involves the heat exchange in models: protein denaturation and starch gelatinization