Influence of extrusion process conditions on the properties of buckwheat products

Abstract

Extrusion has an important role as a manufacturing process in the food industry; it is used to obtain a great variety of products such as baby foods, breakfast cereals, snack foods, pasta, instant powders, modified starches, etc. However, as regards cereals, few studies have examined the application of the extrusion process on less common materials, such as minor cereals and pseudocereals, of interest for their nutritional value. Buckwheat, for instance, is rich in antioxidants, contains rutin, and has a good amino acid profile; moreover, it does not contain gluten proteins, therefore being suitable for the diet of people with celiac disease. The aim of this research was to investigate the influence of different extrusion process conditions (barrel temperature, screw speed, feed moisture) on the chemical-physical characteristics of extruded products obtained from buckwheat. A high fiber buckwheat flour and broken kernels of dehulled buckwheat were used, in order to evaluate the effect of both the fiber content and the particle size of the raw materials on the extrudates' properties. A 3-factor, 3-level Box-Behnken Experimental Design was applied for finding out the relationships between the chemical-physical properties of the extruded samples and the process variables. The barrel temperature and the screw speed each positively influenced the starch damage content and the expansion ratio of the products and negatively influenced their texture, while the feed moisture negatively influenced the expansion of the extrudates. Moreover, for all experimental conditions, good results could be obtained from broken kernels, indicating that starting materials do not necessarily need to be in powder form (e.g., flour)