Rheological properties of sponge cake based on the rice and wheat germ flour

Sponge cake as a snack food has Great popularity among individuals. It seems by fortifying its formulation as a popular snack food, can prepare a functional and nutritive formulation. On the other hand, with increase in sensitivity to gluten and celiac disease, demanding for gluten free or gluten reduced has increased. Due to the importance of proteins forming the viscoelastic gluten network in creating of desirable rheological characteristics of bakery product, the necessity use of proteins with similar characteristics to replace the gluten protein is evident. The aim of this study was to prepare a functional and nutritive product by using rice flour and wheat germ flour as substitute of wheat flour in sponge cake formulation. The cake batter samples were prepared based on 100 percent rice flour, also, wheat germ flour were used at levels of 0, 5, 10, 15, and 20 percent in batter formulations. Also, one sample containing wheat flour was prepared as control. Due to important role of wheat protein in forming of texture of dough and cake, Impact of replacing wheat flour with rice flour and wheat germ flour on dough rheological properties of resulting cake was investigated. After defatted wheat germ flour preparation, cake samples were prepared according to specified formulations. To study the rheological behavior, stable rheological tests (flow behavior) and sweep tests (strain sweep and frequency sweep) on obtained dough were applied by using rheometer equipped with two parallel plates. Results of flow behavior test indicated that all batter samples exhibited thixotropic shear thinning behavior under steady shear tests, which fitted by Power law model and the factors related to this model were specified in the samples. Also, it was observed that batters exhibited weak- gel like properties, by using dynamic oscillatory shear tests and had significant effects on acquired parameters from frequency sweep test, such as storage modulus, loss modulus and tan delta (P<0.05). Sample containing rice flour exhibited weak rheological characteristics compared with control. However, with increasing wheat germ flour levels (from 10 percent to 20 percent), viscosity and consistency coefficient increased, and the combination of rice flour and 10% wheat germ flour was closest to the control. It can be concluded, this is possible to prepare a functional product with desirable rheological characteristics by applying appropriate levels of rice flour and wheat germ flour as wheat flour substitutes in sponge cake formulation