Production of innovative gluten-free breakfast cereals based on red and black rice by extrusion processing technology

The transformation of black and red, broken or not, whole rice grains, into breakfast cereals is an interesting way to add value to these snacks for some reasons. Firstly, broken kernels hardly achieve a high market value; whole rice is healthy not only for their nutrient contents but also for their phytochemical profile, rich in phenolic compounds; breakfast cereals from pigmented rice are colored by themselves, and any additional colorant is unneeded; finally, rice is naturally gluten-free and suitable for those with conditions like celiac disease or gluten sensitivity. The objective of this study was to optimize some extrusion parameters that account for the physicochemical properties of extrudates by using response surface methodology. Feed moisture between 15 and 21% and the 4th barrel zone temperature between 110 and 160 °C were the independent variables. Specific features such as color, texture, water solubility and absorption, cold viscosity, expansion, specific volume, and compression force were evaluated. The trials have shown that moisture had a higher impact on the extrusion process than temperature. Less expanded, denser, harder, and darker products were obtained at higher moisture levels. The optimum points were defined at 15.5% and 16.0% of feed moisture and 159 °C and 150 °C of temperature for black and red rice extrudates, respectively. These conditions resulted in cereal breakfast balls with optimal water solubility, volume, texture, and good color. Additionally, cold viscosities and a low compression led to products with a potential high approval by consumers.