[Protein quality of flatbread and extruded dry flatbread made from full-grain rye groats]

The effect of various processing methods used for the production of dry flatbread from ground whole rye on the nutritional protein quality were investigated by means of the nitrogen balance method in growing rats. The following products were tested: untreated ground whole rye, baked crisp bread, extruded flatbread without and with the addition of 2.5% and 5.0% of saccharose. The apparent protein digestibility (PD) of the 5 samples varied between 69% and 72% and was neither affected by the method of processing nor by the difference in sugar content. Compared to the untreated raw material (NPU = 41%; BV = 59%) net protein utilization and biological value in crisp bread baked by the traditional method (NPU = 35%; BV = 48%) and in extruded flat bread with 5% sugar (NPU = 35%; BV = 51%) were significantly reduced (P less than 0.05). In extruded flatbread without and with 2.5% sugar, NPU and BV of the raw material were essentially maintained. The results indicate that in comparison with the baking process the extrusion of flatbread is more suitable to protect the protein quality. The addition of more than 2.5% sugar caused protein damage in extruded flatbread, presumably as a result of Maillard reactions.