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.