PROCESS OPTIMIZATION WITH RESPECT TO THE EXPANSION RATIOS OF MILLET- AND LEGUME (PIGEON PEA)-BASED EXTRUDED SNACKS

Extruded snacks were made from five blends of millet and legume at varying moisture content (12, 15, 18, 21 and 24%, wet basis [wb]). The percent of legume in the blends were, 12, 16, 20, 24 and 28. Designed experiments were conducted based on central composite rotatable design to determine the optimum processing condition with respect to the expansion ratios of the extrudates. A single-screw laboratory Brabender DA47055 (Duisburg, Germany) extruder was operated at different die head temperatures (160-200C), barrel temperatures (100-140C) and screw speeds (100-140 rpm). The optimum processing conditions obtained using response surface methodology were: moisture content - 19%, wb; blend ratio - 15.7% legume; die head temperature - 190C; barrel temperature - 136.5C and screw speed - 140 rpm. The corresponding expansion ratios viz. specific length, sectional expansion index, longitudinal expansion index and volumetric expansion index were 64.3, 5.5, 0.6 and 3.3, respectively.