Study on the process of single-screw extrusion-cooking of mixtures with a content of pea hulls

A study was conducted on the possibility of application of pea hulls as a valuable source of dietary fibre and of biologically active compounds for the production of cereal extrudates. The research was performed using a single-screw extrusion-cooker with a compression ratio of 3:1 and L:D=12:1, using the following cereal materials: commercially available corn grits, pea hulls of cv. Opal, and oats bran. The aim of the study was to examine the effect of the leguminous material and of the process parameters (profile of barrel temperature distribution and raw material moisture) on the possibility of stabilization of extrusion conditions, physical properties of the extrudates, and on the sensory features of the product. The study showed that the technology of single-screw extrusion-cooking can be applied to process mixtures containing maximum 15% of pea hulls; higher levels of the pea hulls content caused a disturbance of the stability of the process and so-called 'material slippage'. Increase of the pea hulls content in the mixture above 10% caused a decrease in radial expansion and an increase in specific density even up to 140 kg m -3 . Moderate introduction of pea hulls did not result in any deterioration in the texture of the extrudates. The physical properties of the extrudates were significantly affected by the temperature of extrusion and by the raw material moisture content. Increased process temperature resulted in a decrease in radial expansion with simultaneous decrease in specific density of products, increase in crispness and decrease in the WAI of the extrudates. Increase in the moisture of the processed material, on the other hand, resulted in lower radial expansion, increased specific density, and increased water absorption index (WAI) of grinded extrudates. Admixture of pea hulls in amounts up to 7.5% did not cause any deterioration in the sensory features of the extrudate.