Physical and Functional Properties of Twin-screw Extruded Whey Protein Concentrate–Corn Starch Blends

Abstract

Use as a minor component in corn starch extrudates may provide an outlet for underutilized whey protein concentrate (WPC). Several physico-chemical and functional properties of corn starch–WPC extrudates were determined in this study. This information can be used for process scaling-up purposes and for tailoring such extrudates to specific applications. Blends of whey protein concentrate and corn starch were extrusion-cooked with a co-rotating intermeshing twin-screw extruder at 220 g/kg moisture content, 140 rpm screw speed and 140 °C barrel temperature. A split-plot experiment was conducted to investigate four levels of amylose in starch (main plots) with four levels of WPC in WPC–corn starch blends (sub-plots). The design was a randomized complete block with the three replications being three different WPC sources. Studied ranges were 0, 250, 500 and 700 g/kg for amylose and 0, 100, 200 and 300 g/kg for WPC. Measured properties were shear strength (51.4 to 361 kPa), radial expansion ratio (4.32 to 13.1), specific mechanical energy (SME) (240 to 383 J/kg), water absorption index (WAI) (1.98 to 8.57), % water solubility index (% WSI) (9.51 to 67.6%), total color difference (8.08 to 35.9) and % apparent amylose content (0–66%) of extrudates. The WPC source affected several extrudate properties. Data were modeled with polynomial regression. Waxy starch differed from amylose starches in terms of % WSI, WAI, and SME. Significant interactions between levels of amylose and WPC were found for radial expansion ratio, total color change and apparent amylose content. This suggested the presence of a physico-chemical interaction between amylose and WPC.