A novel approach to determine optimal protein texturization conditions - A critical moisture level with increased effect of temperature on viscosity reduction in the rubbery state

Abstract

The effect of moisture on reduction of the flow starting temperature (Tf; i.e. start of flow through a capillary die at constant pressure conditions) in major protein ingredients used in fish feed has been assessed using a Phase Transition Analyzer. All proteins showed an initial linear reduction in Tf followed by a sharp sigmoidal reduction at higher moisture content. A critical moisture level (Mcr) could be defined at the onset of this transition region. Fishmeal and wheat gluten show the lowest Mcr (138 and 160 g kg-1, respectively) and highest reduction in Tf above Mcr. Sunflower meal and soy protein concentrate demand more moisture, show higher variability in Mcr (210–262 and 233–306 g kg-1, respectively) and less reduction in Tf at moisture levels above Mcr. The Tf level corresponds to an apparent viscosity of 105 Pa s and can be combined with the William-Landel-Ferry equation to establish moisture contour plots for the effect of temperature on viscosity reduction in the rubbery state. The protein specific Mcr levels and rheological profiles can be applied to determine optimal moisture and temperature conditions for plasticization and texturization of extruded food and feed products.