Drying rate effect on the properties of whey protein films

The effects of drying temperature, drying relative humidity and film thickness on the drying characteristics, water vapor permeability, and tensile properties of glycerol (Gly)-plasticized whey protein isolate (WPI) films were investigated. 50%WPI:50%Gly and 60%WPI:40%Gly (dry basis) films were studied. Constant rate periods were compared among films. A higher temperature (95C) and lower relative humidity (30%RH) increased the slope of the weight versus time plot during the constant rare period, indicating shorter drying times to reach the falling rate period. Water vapor permeabilities were significantly lower for films dried at 95C and 30%RH than for films dried at 21C and 50%RH. Films dried at 95C and 30%RH were generally thinner stiffer stronger, and less extendable than films dried at 21C and 50%RH.