Optimization of nutrient retention in whole flours extruded from cowpea biofortified grain

Abstract

Whole flour of cowpea grains of the cultivar BRS Tumucumaque biofortified in iron and zinc were processed in a co-rotating twin-screw extruder Clextral HT 25. A central rotational composite design 23, combining temperature (from 86.4 to 153.6 °C), screw rotation speed (from 163.6 to 836.4 rpm) and moisture content (from 16.6% to 23.4%), was used to assess the effects on flour constituents. The three variables significantly affected (p < 0.05) the levels of protein and copper in the extrudates. The reactions of the extrusion process caused a decrease in the levels of proteins and an increase in the levels of copper, zinc and potassium, and these amounts were accentuated as the values of the process variables approached those of the central point region. Extreme conditions at high rotational screw speeds combined with low moisture content reduced the magnesium content, at the opposite end of the values for these two variables, the intensity of the reduction was lower. In the analysis of global desirability, it was found that the extrusion condition at 112.6 °C, 587.4 rpm and 23.4% moisture provided the highest nutrient retention. The levels of iron and zinc remained above 60 and 40 mg kg-1, respectively, in extruded products.