Hydration of heat-treated soy protein isolate and its effect on the molten flow properties at an elevated temperature

The relationship between the flow properties of soy protein isolate (SPI) at 140°C, measured using an extrusion viscometer, and changes in the hydration state were investigated. The state of the water in SPI was analysed by measurement of the freezable water content using differential scanning calorimetry (DSC) and by spin-spin relaxation rate (R₂) measurements using pulsed nuclear magnetic resonance (NMR). The dependence of the flow properties on the state of water was indicated by the correspondence between the water content at which the flow characteristics of molten SPI changed, and the critical water content indicated by DSC measurement of the minimum freezable water content, and by the inflection point in NMR measurement of the spin-spin relaxation rate (R₂).