Water-binding capacity of protein-rich particles and their pellets

The water-binding capacities (WBCs) of pea protein isolate, soy protein isolate, lupin protein concentrate and vital wheat gluten particles were investigated by hydrating them in excess water, centrifuging these dispersions, and calculating the WBCs from the weight of the pellets. It was found that, except for pea proteins, the pellet consisted of a notable amount of interstitial water. Furthermore, it seems that when particles were largely deformable a (semi-)continuous protein network was formed in which individual particles could not be distinguished anymore. Then, the WBC of the pellet did not represent the WBC of the original particles anymore. Consequently, it was concluded that the WBC of the pellet (WBC-P) differs from the WBC of the particles. Therefore, the characteristics of the particles and their pellets were further investigated with, among others, time domain nuclear magnetic resonance (TD NMR). TD NMR turned out to be a useful additional tool to do this, and has the potential to give an indication of the amount of water present in each water domain. From the information obtained about the characteristics of the particles and their pellets, it could be concluded that variations in the WBC-P were the result of differences in the deformability of the particles (i.e., their capability to swell and to withstand the centrifugal force), and their ability to bind water interstitially.