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.

The effect of moisture on reduction of the flow starting temperature (T f ; 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 T f followed by a sharp sigmoidal reduction at higher moisture content. A critical moisture level (M cr) could be defined at the onset of this transition region. Fishmeal and wheat gluten show the lowest M cr (138 and 160 g kg-1, respectively) and highest reduction in T f above M cr. Sunflower meal and soy protein concentrate demand more moisture, show higher variability in M cr (210–262 and 233–306 g kg-1, respectively) and less reduction in T f at moisture levels above M cr. The T f 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 M cr levels and rheological profiles can be applied to determine optimal moisture and temperature conditions for plasticization and texturization of extruded food and feed products. • Sigmoidal reduction in flow starting temperature above a critical moisture level. • The critical moisture level is linked to increased effect of temperature on viscosity reduction in the rubbery state. • Comparison of flow starting temperatures in plant and fish based food proteins. • Mapping of moisture and temperature effects on viscosity reduction. • Variability in rheological properties within commercial SFM and SPC samples. [ABSTRACT FROM AUTHOR]