Thermogravimetric Analysis of Different Semolina Doughs: Effect of Mixing Time and Gluten Content

The thermal properties of different kinds of dough were investigated after different kneading times by means of Thermogravimetric Analysis (TGA). Two varieties of durum wheat semolina were used in this study: Alemanno and Cappelli. The doughs were prepared using a mixograph. The gelatinized flour fraction plays an important role on the thermal properties’ definition, while the mixing time influences the dough network building and consequently the starch gelatinization phenomena. Also, the amount of free water in the dough could be influenced by the mixing time. Thus, the TGA technique was applied in order to evidence the mass loss as a function of the increasing temperature and, from this, the free water content, the residual weight (related to the protein kind and content), and the weight loss rate, i.e. the peaks of the first derivative of the thermogravimetric curve (DTG), which appear at different temperatures and present different heights and positions, depending on the dough network force and extension. In such a way, it was possible to find some correlations between the dough characteristics, like the semolina composition (e.g. the gluten content and quality) and the mixing time, and the thermogravimetric analysis outputs. The results showed that the ratio between free and bond water is strongly dependent on both the mixing time and the semolina variety, and a clear evidence of the protein content in the dough is found because of the position and the size of the peaks in the DTG curve, in combination with the residual mass at fixed temperatures. Proteins, starch and water are the main components of semolina dough. When the ingredients are mixed, several kinds of interactions take place. Understanding the interactions among proteins, starch and water is useful to improve the dough characteristics and, consequently, the final product quality. Thermal analysis is an interesting tool that allows to study the interactions among the dough components in terms of bond formation. Starch gelatinization and protein coagulation phenomena are the main responsible for the thermal properties of wheat doughs. These structures show an effect on the thermal behavior approximately in the same temperature range (55-80 °C) and moisture level. Regarding the proteins, the main role is played by gluten, which is composed by two fractions: the alcohol soluble gliadins, which mainly contribute to the viscosity, extensibility, and cohesiveness of the dough, and the alcohol in