Effect of crosslink density on the water-binding capacity of whey protein microparticles

The ability of whey protein microparticles (MPs) to bind water and consequently to swell is, amongst others, determined by the crosslink density of the MPs. The Flory-Rehner model states that a decrease in crosslink density should lead to an increased swelling of the MPs. Decreasing the crosslink density of MPs with dithiothreitol (DTT) decreased the amount of disulphide bridges and increased the water-binding capacity (WBC) from 6 to 9 g water/g protein. Increasing the crosslink density with transglutaminase or genipin resulted in a decreased number of primary amino groups, although the WBC did not change significantly. The WBC of the MPs was determined using a centrifugation method that resulted in the formation of a pellet, so water inside and between the MPs was measured simultaneously. Therefore, additional microscopy and swelling tests were performed, which suggested that an increased WBC of the pellet of MPs was not only related to an increased swelling of the MPs, but also to an increased amount of water between the MPs.