EFFECT OF PARTICLE SIZE DISTRIBUTION OF RAW MATERIALS ON EXTRUSION COOKING PROCESS AND QUALITY OF COMPOSITE SNACKS

Rational selection of composition particles size distribution is an important factor for extrusion technology of high quality snack production. Influence of the milling rate of rice, millet, buckwheat and lentil on extrusion cooking regimes and technological parameters of extrudates was investigated. Decreasing of hammer mill sieve openings from 5 to 1 mm resulted in increasing of small fraction with size below 0.2 mm for rice from 18.2 to 60.0%, for millet from 33.5 to 82.0%, for buckwheat from 18.0 to 56.0%. This allowed obtaining composition with more uniform particle size distribution. Investigation of extrusion cooking process showed increasing of torque and pressure at extruder die with decreasing of composition particles size. The shift of the sieve openings frommm to 1.0 mm caused 10.0% increase of extrusion energy consumption. Reduction of the particles size increased the extrudate expansion rate coefficient from 8.8 to 13.0, the water absorption index from 8 to 8.35 g/ g of dry matter and solubility from 22 to 37%. Moreover it caused a significant reduction in the bulk density from 137 to 82 kg/m3. This trend changed the texture of the extrudates to a more delicate structure. The hardness of the product was reduced from 9.8 to 6.1 H at a constant value of the fractures number.