Protein rich extruded products from tef, corn and soy protein isolate blends

Abstract

Specific blends of Tef, corn and soybean protein isolates (SPI) were subjected to twin screw
extrusion process with the objective of enriching the protein content of Tef and produce a
range of extruded products. The proportions of Tef, corn and SPI were selected using a
unique 16-run, three-factor, three-level D-Optimal constrained mixture design. The SPI
addition was maintained in the 0-20% range to test the effect of protein addition to the cereal
mix (Tef and corn accounting the balance 80-100%) on the physical properties of the extruded
products. Extruded products were obtained using a co-rotating twin screw extruder under
operating conditions optimized in a previous study. The study showed significant differences
(p<0.05) in color value, rehydration ratio and water solubility index while there were no
significant differences among the products in terms of expansion ratio and bulk density. In
general, proportion of ingredients induced significant changes in the product quality
attributes evaluated. Blends with higher proportion of Tef and SPI (lower proportions of corn)
showed a significantly (p < 0.01) lower L* value, b* value and higher levels of product
hardness. It was demonstrated that Tef has good potential for making good extruded
products. The formula containing 20% Tef, 60% corn, and 20% SPI was selected as the best
formulation to yield a protein rich extruded product with desirable attributes. Understanding
the effect of these variables on the product physical properties was deemed useful for the
development of protein-rich extruded products.