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

Abstract

The glass transition temperature (Tg), 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 (ɑw) values between 0.80 and 0.90. MPI hydrolysates displayed reduced Tg (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.