| Extrusion of pigeonpea and Basmati rice was carried out to find out if there are optimum extrusion conditions in terms of the processing variables that give desirable physico – chemical properties to extrudates. Pigeonpea is a nutritionally dense legume. Because extrusion can produce low moisture and long shelf life products, it would be useful to make pigeonpea available to wider market. High protein content of pigeonpea may limit its use as an extrudable material because high proteins concentration usually curtails expansion. Basmati rice, being a traditional supplement and rich in starch, can provide an aid for expansion when mixed with pigeon pea flour.;A Brabender single screw extruder was employed for the extrusion of Basmati rice and pigeonpea flour mixture. Four factors of importance chosen for this study were: ratio of whole pigeonpea to Basmati rice (25 % to 75 %), barrel temperature (120 °C-160 °C), moisture content (19- 24 %), and screw speed (120-180 RPM). Response surface methodology (central composite design, CCD) was first used to design experiments. Based on results of the CCD design, a three factor Box-Behnken design (BBD) was employed which focused on the impact of three major parameters, namely, the temperature of the barrel (120 °C-160 °C), the moisture content (19- 24 %) and the screw speed (120-180 RPM) on extrudate properties.;The fraction of pigeonpea in the mixture that could provide acceptable expanded product with sufficient amount of protein was 0.5 or 50%. The processability was not significantly affected up to 50 % pigeonpea in the mixture. The particle size distribution (PSD) had significant effect on the physico-chemical properties of extrudate.;Moisture content of the finished product was inversely proportional to the barrel temperature. An increase in temperature and/or screw speed caused a decrease in bulk density of the extrudate. Water solubility index (WSI) and water absorption index (WAI) increased with increase in barrel temperature. WSI was also influenced by fraction of pigeonpea in the mixture with a positive correlation. An increase in the screw speed reduced the brown color and increased the brightness of the extrudate to some extent. |
