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UBC Theses and Dissertations

Investigation of vitamin D3 content in fortified fluid milk and the stability of vitamin D3 in milk to light exposure Liu, Yang


Fortified milk is the main dietary source of vitamin D, an important nutrient for skeletal health and reducing the risk of some chronic diseases. However, non-compliance of vitamin D fortification of fluid milk has been reported as a recurring problem. The purpose of this research is to analyze vitamin D contents of fortified fluid milk sold in Vancouver, the stability of commercial vitamin D formulations in milk upon light exposure during refrigerated storage, and the thermal stability of vitamin D₂ and D₃. Vitamin D content was determined for 104 fluid milk products purchased from the Vancouver retail market from October 2011 to September 2012. Fortification non-compliance was defined as vitamin D levels outside the range of 35.2-46.9 IU/100 mL, corresponding to regulatory requirements stated by the Canadian Food Inspection Agency. The results showed 54% under-fortification and 4% over-fortification with significant variation in vitamin D content among milk from different brands, with different fat content and sampled at different times. In particular, higher incidence of under-fortification was observed in skim milk samples. To investigate the stability of vitamin D₃ to light exposure, skim milk was fortified with one of four vitamin D₃ formulations along with vitamin A: crystalline vitamin D₃, two water dispersible formulations and an emulsified vitamin A/D premix. Vitamin D loss after 22 days of storage at 4 °C with exposure to light of 2000 lux intensity ranged from 37% to 71% depending on the different formulation, and was accompanied by vitamin A loss. To investigate the effects of pH and heat on stability, vitamin D₂ and D₃ in citrate-phosphate buffer at pH 3.5 and 6.6 were heated at 72 °C for 15 seconds. Less than 8% vitamin D loss was observed. No significant difference was found in thermal stability between vitamin D₂ and D₃ or between the pH conditions during heating. These results indicate the possible approach to improve vitamin D fortification compliance in fluid milk by choosing a vitamin D formulation with improved dispersibility and greater stability against light exposure. Further research is needed to investigate other potential factors affecting the vitamin D content in fortified milk.

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