Stability and bioavailability of vitamin D encapsulated in whey protein microgels

Whey protein isolate (WPI) microgels were used as a carrier to effectively encapsulate and protect vitamin D (VD). Cold-set gelation was used to prepare the VD loaded WPI (WPI-VD) microgels, whereby WPI was heat-denatured, cooled, VD was added followed by the addition of calcium chloride to induce WPI microgel formation. The WPI-VD microgels were tested for their encapsulation efficiency, stability against temperature (72°C for 15s or 63°C for 30min), UV-light (254 nm) and four-week storage (4, 20 and -20°C). A static in vitro digestion model was used to assess the gastrointestinal behaviour of WPI-VD microgels. The WPI microgels exhibited high encapsulation efficiency of >98% and the incorporation of VD did not significantly change the particle size. Moreover, the WPI microgels significantly improved the stability of VD compared to the control (unencapsulated VD) when exposed to environmental conditions. When heated the microgels provided a protective barrier to VD as 97% remained, whereas unencapsulated VD degraded by 26%. UV-light exposure led to complete degradation of VD, however, when encapsulated, 97% VD remained. The microgels could prolong the shelf life of VD as >92% remained intact at the end of the fourth week compared to ~70% for the control, irrespective of storage temperature. The oral and gastric phases of in vitro digestion revealed negligible VD release from the microgels. However, when the microgels entered the intestinal phase, 17% VD was released after 30 minutes, followed by 97% VD release at the end of digestion. This indicates that the microgels can protect VD through early digestion and release at the optimal phase for absorption in the small intestine. The current work demonstrates that WPI microgels can effectively encapsulate VD, protect against environmental factors, and release VD at the optimal gastrointestinal location which have potential applications in food systems.