Investigation of bioaccessibility of vitamin D3 encapsulated in micro/ nanoemulsion through in vitro digestion model

Vitamin D (calciferol) is a fat-soluble vitamin that plays a role in calcium and phosphorus metabolism and bone mineralization. It is found as D2 (ergocalciferol) in plant sources and D3 (cholecalciferol) in animal sources. Current data indicate that individuals have difficulty in meeting their daily vitamin D requirements through diet and sun exposure. Due to the lipophilic nature of vitamin D, which is sensitive to UV light, oxygen, and various environmental conditions, several encapsulation-based studies have been conducted in the literature to protect it from potentially adverse effects during food processing and to increase its bioaccessibility and bioavailability within the digestive tract. In this study, it was aimed to characterize and determine the stability of vitamin D3 (vitD3) by encapsulating it in micro/ nano emulsion (ME/ NE) and to investigate the level of vitD3 bioaccessibility of vitD3-loaded ME/ NEs as they pass through the simulated digestive system of the small intestine. Following physical, morphological, and structural analyses, the two selected formulations were analyzed for bioaccessibility of vitamin D3 during digestive processes. A total of 4 emulsion formulations were created using hydrolyzed and non-hydrolyzed whey protein concentrate (80% WPC and HWPC) with oil: water phases and containing 50,000 IU and 200,000 IU of vitamin D. In the formulations, droplet sizes measured microscopically and by light scattering were found to range from 100 nm to 10 µm, with droplet size increasing as the oil phase ratio increased. The most significant difference between emulsions prepared with WPC and HWPC was that those prepared with HWPI were remarkably clearer. While clarity has been associated with smaller droplet sizes in nanoemulsion studies, size measurements in this study did not reveal a clear size difference between the two groups. ME/ NEs were generally stable for 10 days at +4°C and did not undergo phase separation, although a slight increase in droplet size was observed. These results demonstrate that the designed ME/NE systems are successful in delivering vitamin D to the stomach and, particularly, the intestines, and increasing its availability. The study findings provide a potential model for the production of highly bioavailable functional dairy products enriched with micro/nano-encapsulated vitamin D. Future studies will further enhance knowledge by conducting more detailed analyses and contributing to the commercialization of these products.