Rehydration and water sorption behaviour of bovine milk protein isolate and its associated enzymatic hydrolysates

The glass transition temperature (T_g), moisture sorption and rehydration properties of bovine milk protein isolate (MPI) and MPI hydrolysates generated with Flavourzyme™, Neutrase™ and Protamex™ [degree of hydrolysis (DH) ranging from 15.6 to 37.1%] were evaluated. MPI hydrolysates displayed reduced water droplet contact angles (<50°) compared with intact MPI (∼90°), indicating increased wettability. The aqueous solubility of the hydrolysates was increased (72–100%) compared with intact MPI (∼30%) at 25 °C. The hydrolysates had higher moisture contents (40–50%) than intact MPI (∼27%) at water activity (ɑ_w) values between 0.80 and 0.90. MPI hydrolysates displayed reduced T_g (48.5–67.3 °C) compared with intact MPI (∼121 °C), indicating reduced stability. Overall, enzymatic hydrolysis enhanced the properties of MPI; this improvement was enzyme dependent and increased with increasing DH. Manufacture of hydrolysate ingredients with a controlled moisture content and storage at controlled ambient temperatures is proposed to maintain the improved rehydration properties.