Supercritical carbon dioxide extrusion of milk protein concentrate and rice flour blend: A new dairy nutrition delivery platform

Abstract

The main objective of this study was to develop milk protein concentrate (MPC) and rice flour blend ready‐to‐eat extrudates using supercritical fluid carbon dioxide extrusion (SCFX) that have comparable physical characteristics with selected commercial products because the conventional, steam‐based extrusion process is a high‐temperature and high‐shear process that degrades the product quality. Three formulations, in the ratio of 30:66.5, 60:36.5, and 90:6.5 of MPC:rice flour, were blended with 2% emulsifier (dimodan and lecithin) and 1.5% salt. The blended formulations were extruded using a Wenger twin‐screw extruder designed and built for use with supercritical CO2. The mechanical and physical properties of the extrudates were determined and compared with two commercial carbohydrate cereal products. The extrudates were equilibrated to 43%, 23%, and 11% relative humidity (RH) and their stress and stain relationships were quantified. The power law model was used to model the modulus of elasticity of the extrudates with a good fit (R2 = 0.98–0.99). The extrudates and commercial samples were rehydrated until attaining their equilibrium moisture contents and the data were used to model the rehydration kinetics and determine the diffusivity values using Fick's law. The results revealed that MPC (30%–90%) and rice flour (66.5%–6.5%) blend extrudates had physical and mechanical properties that were within the range of commercial samples tested. The overall findings of this study indicated that the physical characteristics of extrudates containing 60% and 90% MPC can be successfully used to produce ready‐to‐eat cereals and high MPC nutribars.