Influence of Soy Protein Hydrolysates on Thermo-Mechanical Properties of Gluten-Free Flour and Muffin Quality

The influence of protease-assisted hydrolysis on the impact exerted by the soy protein isolate on the thermo-mechanical behavior and baking performance of the gluten-free composite flour, consisting of a mixture of rice and quinoa flours, was investigated. The mPAGE analysis revealed that soluble fractions of the hydrolysates, obtained with bromelain, Neutrase or trypsin, concentrated the peptides with a molecular weight lower than 20 kDa, whereas the insoluble ones retained higher molecular weight fragments. The influence of the separate and cumulative addition of the soluble and insoluble soy peptide fractions on the thermo-mechanical properties of dough was tested by means of a Mixolab device. Regardless of the enzyme used for hydrolysis, the addition of the soluble peptide fraction to the gluten-free composite flour resulted in delayed starch gelatinization, whereas the insoluble one caused a considerable increase in the dough consistency. The most important improvements in the dough behavior were observed when supplementing the gluten-free flour with 10% soy protein hydrolysates obtained with bromelain and trypsin. The gluten-free muffins enriched in soy protein hydrolysate exhibited important differences in terms of moisture, height and specific volume, compared to the control. Moreover, the ABTS- and DPPH-based methods indicated that protein hydrolysate addition caused a significant improvement in the antioxidant activity (by at least 38% and 23%, respectively) compared to the control. In conclusion, soy protein hydrolysate might be successfully used for increasing both the protein content and the antioxidant activity of the muffin samples.