Effect of hydrocolloids on structural and functional properties of wheat/potato (50/50) flour dough

Physicochemical analyses were performed to study the effect of hydrocolloids on wheat/potato (50/50) flour doughs. Pectin, hydroxypropilmethylcellulose, Arabic gum and konjac glucomannan were tested at 1.5 g/100 g (flour basis). Textural and rheological assays indicated great differences between the control dough (100 % wheat flour) and doughs containing wheat/potato flour (50/50). These differences were reduced when hydrocolloids were added with Arabic gum and hydroxypropilmethylcellulose being the gums that better mimic the control dough properties. The analysed dough showed a bimodal distribution of relaxation times indicating that more than one molecular mechanism was responsible for relaxation. The presence of potato flour led to a marked decrease in relaxation times indicating a faster decay of stress as a function of time. The presence of gums probably increased relaxation times by establishing stronger non-covalent interaction with the dough components, rendering high molecular weight aggregates, which slowed down relaxation behaviour. Differential scanning calorimetry results showed that potato flour did not significantly changed the gelatinization temperature, but the addition of hydrocolloids shifted this parameter to higher values. Samples containing gums broadened the endotherm making the process slower and more energy demanding. The microstructure was studied at different levels (optical, confocal and scanning electron microscopy) and it was observed that potato flour made the microstructure smoother and more uniform. On the other hand, the addition of hydrocolloids led to rougher structures. These observations were confirmed by modelling image texture with different algorithms such as grey level co-occurrence matrix, fractal dimension and lacunarity.