Vitamin B12, folate and folate-binding proteins in dairy products

Vitamin B12 and folate are two important B vitamins for maintaining good health, being involved in amino acid metabolism and DNA synthesis. Milk and dairy products are good sources of vitamin B12 and folate. Moreover, they are of interest due to their content of folate-binding proteins (FBP), since it was hypothesised that these promote folate bioavailability. Furthermore, fermentation of milk is a way to increase the content of both vitamins. Vitamin analysis in fermented dairy products is complicated due to the complex matrix. To gain reliable data on vitamin content, retention and bioavailability, emphasis throughout the project was put on optimisation and evaluation of methods for quantification. A commercial radio protein-binding assay (RPBA), produced for clinical samples, was evaluated regarding, e.g. assay pH, buffer molarity and food matrix effects. The optimised RPBA was demonstrated to be suitable for quantification of vitamin B12 in milk and fermented dairy products, and of folate quantification in dairy samples containing mainly 5-methyl-tetrahydrofolate. One aim of this project was to map the retention of vitamin B12 and folate during manufacture of six fermented dairy products. Results showed, e.g. that fermentation of milk followed by storage at 4 °C for 14 days decreased vitamin B12 concentrations in fermented milk by 40-60% compared with concentration in the milk. However, vitamin B12 was 4-7-fold concentrated during hard cheese making. Regarding folate, the concentrations of folate increased both during fermentation of milk to yoghurt and during manufacture of cheese. Another aim was to study folate bioavailability from milk and fermented milks using both an in vitro gastrointestinal and a human model. Focus was on studying the stability and the nutritional role of bovine milk FBP, which are suggested to have a positive impact on folate bioavailability. Both studies showed FBP to partly endure in vitro and in vivo gastrointestinal passage, and further, to decrease in vitro and in vivo folate bioavailability