Calcium content of milk
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Calcium Content in Milk: Key Values and Variability
Milk is widely recognized as a major dietary source of calcium, with typical concentrations in raw cow's milk ranging from 700 to 1,100 mg per liter, and average values often cited between 900 and 950 mg/L . These values can vary depending on several factors, including breed, diet, season, and processing methods 123.
Factors Affecting Calcium Levels in Milk
Breed and Genetics
Different cow breeds produce milk with varying calcium content. For example, Holstein cows generally have lower milk calcium levels compared to Montbéliarde and Normande breeds, with Normande cows producing milk with the highest calcium content among the three 23.
Lactation Stage and Parity
Calcium content in milk changes throughout the lactation period. It tends to decrease during the first month after calving and increases after the fourth month. Additionally, as cows have more lactations (higher parity), the calcium content in their milk tends to decrease 23.
Diet and Feeding Strategy
The type of feed significantly influences milk calcium levels. Cows fed fresh or conserved grass (as opposed to corn silage) tend to produce milk with lower calcium content, especially in the spring during grazing periods 238. Dietary mineral balance, such as the dietary anion-cation difference (DCAD), also affects calcium levels, with higher DCAD diets increasing milk calcium content .
Seasonal and Environmental Effects
Seasonal changes, such as longer daylight hours and higher temperatures in late spring and summer, are associated with a decrease in milk calcium content. This seasonal drop is observed regardless of breed or diet, although the effect is more pronounced in some feeding systems 138.
Calcium in Processed and Fortified Milk
Processing methods and fortification can alter the calcium content and its bioaccessibility in milk. Pure, unprocessed milk generally has optimal calcium levels compared to processed variants with additives . Fortified milks, especially those using advanced technologies like solid dispersion emulsification or solid-in-oil-in-water emulsions, can achieve higher calcium stability and improved bioaccessibility compared to traditional fortification methods 69. However, excessive calcium addition can lead to aggregation and reduced stability in the milk 69.
Forms and Bioavailability of Calcium in Milk
Calcium in milk exists in both ionized and complexed forms, primarily bound to casein, citrate, and phosphate. The ionized calcium concentration is typically around 2.5 to 3.4 mM/L 57. The bioavailability of calcium from milk is high, especially when the calcium is balanced with phosphorus and present in its natural, easily digestible form 17. Fortification methods that improve dispersion and prevent aggregation can further enhance calcium bioaccessibility 69.
Practical Implications for Dairy Processing
Manipulating calcium content in milk affects not only its nutritional value but also its processing properties. Changes in calcium concentration can influence thermal stability, gelation, coagulation, and foaming, which are important for various dairy products . Both the addition and removal of calcium must be carefully managed to maintain product quality and functionality .
Conclusion
The calcium content of milk is influenced by a complex interplay of genetic, dietary, seasonal, and processing factors. While raw cow's milk typically contains 700–1,100 mg/L of calcium, this value can fluctuate based on breed, lactation stage, feed, and environmental conditions. Advances in fortification and processing technologies are helping to improve the stability and bioaccessibility of calcium in milk, ensuring it remains a vital source of this essential mineral in the human diet.
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