Thermo-mechanical behaviour of dough and bread making properties of soryz flour

Abstract

Soryz (Sorghum oryzoidum) is a relatively new gluten-free cereal of hybrid origin from sorghum with potential in developing gluten-free products. The rheological behaviour of soryz in terms of thermo-mechanical properties assessed by Mixolab system was studied in comparison with other gluten-free sources from cereals (rice, oat, teff), pseudo-cereal (quinoa) and legume (soy). Soryz showed an atypical Mixolab curve with very low consistency until the gelatinisation temperature was reached. Soryz presented weaker protein network, lower water absorption and stability than other flours. Whole oat was characterised by the strongest protein network. Soy and whole oat flours had the highest water absorption, development time and improved stability as compared to the other samples. A positive correlation was found between protein weakening and dough stability (r=0.88; P<0.05). Soryz flour was characterised by higher starch swelling and, consequently, starch retrogradation also increased with increasing starch gelatinisation. A higher starch content was correlated with higher gelatinisation (r=0.76; P>0.05). A negative correlation was found between starch gelatinisation and protein content (r=-0.66; P>0.05) as well as lipid content (r=-0.77; P>0.05) of the gluten-free flours. The behaviour of soryz flour during mixing and heating with the help of Mixolab brings useful information in the development of gluten-free bakery products. Bread formulations on soryz flour as well as soy-soryz blends (5 and 10% soy flour addition) were tested for improving bread nutritional value. Addition of soy flour in soryz bread formulations, decreased the bread volume, porosity and lightness as well as increased hardness in comparison to soryz bread control.