Vitamin K in Grassfed and non-Grassfed dairy: Quantification, effect of intake and measures of bioaccessibity

This thesis examined the impact of bovine diets and lactation stages on vitamin K levels in dairy products, and compared the effects of pasture-fed versus total mixed ration (TMR)-fed Cheddar cheese on human vitamin K status and bioaccessibility. The study aimed to understand how different feeding methods influence the vitamin K content and bioavailability in cheese, and it effect on human health. Chapter 2 focused on developing a safer and more efficient method to extract and quantify vitamin K (K1, MK-4, MK-7, MK-9) in dairy products. Cheddar cheese and butter samples were analysed using an improved HPLC method with a fluorescence detector, replacing hexane with the less toxic solvent heptane. The method showed improved LOQ for MK-4 and MK-9 and showed high precision and stability. This validated approach is effective for measuring various vitamin K forms in Cheddar cheese and butter. Chapter 3 investigated the vitamin K content in butter and Cheddar cheese produced from cows fed pasture (GRS), total mixed ration (TMR), or partial mixed ration (PMR) diets at different lactation stages. Findings indicated that pasture-fed milk products had higher K1 levels, with GRS butter showing the highest MK-4 content. Mid-lactation butter and late-lactation cheese had the highest vitamin K concentrations, emphasizing that both diet and lactation stage significantly influence vitamin K levels in dairy products. A higher pasture-fed ratio was found to enhance vitamin K content, particularly K1 and MK-4, suggesting changing the bovine diet could enhance vitamin K levels in dairy products. Chapter 4 explored the effects of pasture-fed versus TMR-fed Cheddar cheese on vitamin K status biomarkers in humans. Using samples from a previous trial involving overweight adults over 50 years old, participants consumed either pasture-fed or TMR-fed cheese for six weeks. Despite the TMR cheese containing nearly double the vitamin K levels compared to pasture-fed cheese, both types resulted in similar improvements in vitamin K status biomarkers, such as dp-ucMGP and the ratio of ucOC to cOC. This suggests that the vitamin K bioaccessibility in pasture-fed cheese may be higher than in TMR cheese, compensating for its lower total vitamin K content. Chapter 5 compared the bioaccessibility of vitamin K in pasture-fed and TMR-fed Cheddar cheese using an in vitro digestion model (INFOGEST 2.0). Results showed that pasture-fed cheese had significantly higher bioaccessibility of K1 and MK-4 compared to TMR cheese, possibly due to differences in texture, unsaturated fatty acids, interactions with casein, and physicochemical properties of vitamin K forms. These findings imply that the matrix of pasture-fed cheese may enhance the absorption of vitamin K more efficiently than TMR cheese. Overall, the research highlights that pasture-fed bovine diets can significantly increase vitamin K content in dairy products and that pasture-fed Cheddar cheese may offer better vitamin K bioaccessibility than TMR-fed cheese. This improved bioaccessibility potentially leads to more effective enhancement of vitamin K status in humans, indicating that diet and feed types play crucial roles in optimizing the nutritional quality of dairy products.