Glass transition temperatures of cassava starch-whey protein concentrate systems at low and intermediate water content

Glass transition temperatures of cassava starch (CS)-whey protein concentrate (WPC) blends were determined by means of differential scanning calorimetry (DSC) in a water content range of 8-20% (dry basis, d.b.). Water equilibration in the samples was carried out by storing them at room temperature (25 °C) during four weeks. Physical aging and phase segregation were observed in some samples after this storage period depending on the water content. Both, first DSC heating scans and tan δ curves of CS-WPC blends with intermediate water content (10-18%), showed two endothermic thermal events. The first one appeared at around 60 °C and was independent of water content. The second one was detected at higher temperatures and moved towards the low-temperature peak as the water content increased. The results can be explained by a phase segregation process that can take place when the samples are conditioned below their glass transition temperatures. The Gordon-Taylor equation described well the plasticizing effect of water on the blends. WPC was also found to decrease the glass transition temperature, at constant water content, an effect attributed to additional water produced during browning reactions in the blends.