The effect of pH on the wetting and dissolution of milk protein isolate powder

Milk protein isolate (MPI) powder is an important food ingredient powder but it has poor wettability and dissolution ability which limit its functional usage. The effect of pH (5.4-8.4) on the wettability and dissolution of MPI powder is evaluated in this study. Contact angle and Washburn methods were used to measure the wetting behaviour of MPI powder. Its dissolution ability was measured by static light scattering in real-time after a pre-mixing step. The results showed that the contact angle of droplets on compacted powder tablets exhibited no significant difference between pH conditions (p>0.05) and this was supported by the results of the Washburn method. It was found that MPI dissolution was strongly correlated with the appearance of submicron size casein micelles in the solution. During dissolution, higher pH caused an earlier appearance of this casein micelle submicron peak and a higher swelling peak associated with the swelling of casein micelle aggregates. This swelling of casein micelle aggregates indicates greater water penetration and loosening of the aggregate structure at higher pH, which facilitated faster dissolution of MPI powder, especially at a pH of 8.4. This study indicates changing alkaline environment could be potential to apply in MPI rehydration.