Adsorption of milk proteins onto rice starch granules

The adsorption of sodium caseinate (NaCAS) and whey protein isolate (WPI) to both normal and waxy rice starch granules was investigated using SDS-PAGE. This showed that the proteins present in NaCAS and WPI do adsorb to normal and waxy rice starch granules and that in the case of NaCAS, for both normal and waxy rice starch, αs-casein adsorbed preferentially and in higher amounts than β-casein. In the case of WPI, although the amount of adsorbed β-LG is higher than that of α-LAC, no preferential adsorption is observed. Confocal laser scanning microscopy, with specific dyes, was also used in an attempt to locate the milk proteins adsorbed to the starch granules. The adsorption isotherms of these two milk protein ingredients to rice starch granules, were modelled using the BET equation which is usually used to model multilayer adsorption, and a simple equation is proposed to take into account possible absorption of the proteins into the core of the starch granules. Good agreement is found between these models and the experimental results. Possible mechanisms involved in the interaction between milk proteins and starch granules are discussed.