Modelling to obtain expanded cowpea products in a twin screw extruder

Abstract

Cowpea grains are nutritious and beneficial to health, contain about 25% of proteins, in addition to carbohydrates, vitamins, minerals, and bioactive compounds. Soaking the beans followed by cooking requires time availability that is incompatible with the current lifestyle. Consumers have opted for read-to-eat, attractive, healthy, nutritious and convenient foods, thus, transforming cowpeas into crispy expanded product is promising. This research aimed to evaluate the effect of the extrusion conditions, moisture, and temperature, on the physical characteristics of the extrudates developed from cowpea cotyledons flour (CCF): from cultivar BRS Guariba (Sorriso, MT, Brazil). The CCF was processed using twin-screw thermoplastic extruder ZSK 30 (Werner & Pfleiderer Co.) varying the moisture (16.2% to 21.8%) and temperature (124 to 166 °C) using Central Composite Rotatable design 22. The expansion index values ranged from 3.01 to 3.98, the regression model was not predictive, with the determination coefficient (r2) equal to 0.67. The independent variables studied presented significant effects, being water solubility index affected by the CCF moisture, compression force (15.63 to 47.72 N) affected by the extruder temperature, the water solubility index (28.34% to 43.67%) by moisture, while the specific volume (2.41 to 4.58 mL g-1) and the water absorption index (5.34 to 6.54 g g-1) were affected for both variables. By simulation, the maximum value of 1 was obtained through the global desirability test in the combination of an extrusion temperature of 124.21 °C and conditioning moisture of CCF of 16.28%. This condition favors obtaining extrudates with greater values for a specific volume and water absorption index, and lower values for compression force and water solubility index.