The effect of extrusion variables on physical and functional properties of expanded breakfast cereal based on whole oleaster and oat flours

With regard to the importance of breakfast cereal in today's eating habit, these products can serve as vehicles for the main nutrients. Therefore, the purpose of this research was to investigate the effect of extrusion variables containing replacement level of whole oat flour with whole oleaster flour (10, 25 and 40%), feed moisture (14, 18 and 22%) and screw speed (120, 150 and 180 rpm) on some physical and functional properties of breakfast cereal. These properties included moisture content, bulk density (BD), hardness (HD), water solubility index (WSI) and color parameters assessed by central composite rotatable design. Based on the obtained results, an increase of the whole oleaster flour and feed moisture increased the moisture content and hardness and decreased the yellowness of the samples. While the water solubility index was increased by increasing the whole oleaster flour and was decreased by increasing the feed moisture. The evaluation results of the screw speed indicated that increasing the speed resulted in less bulk density, hardness and water solubility index. Additionally, the lightness of samples decreased due to a higher amount of all the variables studied. On the one hand, the difference between ingredients content and structure of the whole oleaster flour and the whole oat flour was one of the most effective factors on the obtained results. On the other hand, the influence of the feed moisture and screw speed, as very important factors of the extrusion process, on the physical and functional properties of the product was completely recognized. Optimum condition was found to the blends of whole oleaster flour/whole oat flour (10:90), screw rate of 180 rpm, and feed moisture content of 22% with desirable properties including humidity(10.26%), bulk density (0.11 g/cm3), hardness (11.01 N), water solubility index (12.66 %), lightness (56.09).