Vitamin D3 formation in milk by UV treatment – Novel insights into a rediscovered process

Abstract

Vitamin D3 is essential for several functions in the human body and the demand is usually covered by natural reactions in skin with UV radiation delivered by the sun. But living beyond a latitude of 35° can lead to a lack of sufficient exposition to the deciding wavelength. Here, many countries fortify their milk prophylactically with artificial vitamin D3. However, the precursor molecule of vitamin D3 (7-deydrocholesterol) is already naturally located in the milk fat globule membrane. Thus, this study deals with the transformation of the naturally occurring 7-dehydrocholesterol into vitamin D3 through UV treatment of the milk - a mechanism that was observed a century ago only indirectly. Different parameters such as temperature (10 - 50°C), fluid flow regimen (turbulent vs. laminar thin film, i.e., 0.6 mm) and wavelength (254, 280 and 313 nm) were investigated in this study for their efficiencies. The UV dose of each experiment was measured with chemical actinometry delivering the actually applied dose reaching the milk. Thus, the connection between applied UV dose and generated vitamin D3 content in the milk measured quantitively with LC-MS/MS was evaluated here that both were not possible a hundred years ago. The experimental results revealed that temperature generally promotes the vitamin D3 formation at 254 nm. Further, a turbulent flow is not as efficiently treated as a laminar thin film flow that is as narrow as 0.6 mm. As expected from absorbance spectra of the precursor molecule 7-dehydrocholesterol, 280 nm turned out to be the most efficient wavelength, followed by intermediate success through irradiation with 254 nm and almost no effect by 313 nm. Generally, it was shown that vitamin D3 concentration of milk was easily increased by UV treatment with today's technologies and that adjustment of certain physical parameters have a significant effect on the efficiency.