The effect of vitamin D on the foaming properties of whey protein isolate microgels

Whey protein isolate (WPI) microgels were used as a carrier to effectively encapsulate vitamin D (VD). The microgels will be incorporated into foamed foods as a delivery vehicle and thus, their ability to form and stabilise foams was analysed. Cold-set gelation was used to prepare the microgels, whereby WPI was heat-denatured, cooled, VD was added followed by 0.1M calcium chloride to induce gelation. The microgels were characterised by particle size, rheological properties and on their foam ability and texture. The foamability of VD loaded WPI (WPI/VD) microgels were analysed and compared with unloaded WPI microgels. Mechanical whipping was used to prepare the foams which were assessed on overrun and stability. The microgels had an encapsulation efficiency of >98% and the incorporation of VD did not significantly alter particle size. Rheological data indicated that for both microgel systems, G' was greater than G'' indicating a more solid-like structured behaviour. The incorporation of VD resulted in a decrease of the storage and loss moduli compared to the unloaded WPI microgels. After mechanical whipping, the foam overrun, and stability were not significantly different comparing the WPI and WPI/VD microgels, with foam overrun values of 361 and 345% respectively. After four-week storage at 20, 4 and -20°C, there was approximately 50, 25 and 0% liquid drainage respectively from both microgel foams. Texture analysis indicated that the addition of VD reduced the foam firmness and consistency of the microgel foams. This work demonstrates that WPI microgels can be used as a functional application for creating stable foams, and that VD does not have a negative impact on the foamability of the microgels. The unique properties of microgel stabilised foams have much to offer in developing the science of food structuring and formulating novel delivery structures for the food industry.