The purpose of this study was the investigation of the effect of process conditions (temperature, feed rate) and raw material characteristics (moisture content, fiber to corn ratio) on structural and mechanical properties (apparent/true density, porosity, expansion ratio and stress of compression) of corn based extrudates enriched with apple and oat fibers. Simple power models were developed to predict porosity and compression stress as functions of process conditions and material composition. The extrusion conditions regulated were the feed rate (0.5-2.0 g/s) and the extrusion temperature (150-230°C), at a speed of screw rotation of 200 rpm. The feed material moisture content was regulated from 13 to 19% (wet basis) and the fiber to corn ratio was ranged from 10 to 30% for both types of extrudates. Porosity of extrudates was found to decrease with temperature, feed moisture content and fiber to corn ratio and to increase with feed rate for both the examined fibers. The same tendency was also found for the expansion ratio of extrudates, while the stress of compression revealed the opposite behavior. The true density of apple fiber/corn extrudates ranged at 1550±387 (kg/m~3), while that of oat fiber/corn ranged at 1450±207 (kg/m~3). Comparatively, the use of apple fibers led to products with higher porosity, compared to those with oat fibers. In general, the addition of fibers resulted to more dense products.
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