Selenium binding and distribution in goat and cow milk

Area of Science:

• Dairy Science
• Nutritional Biochemistry
• Food Chemistry

Background:

• Selenium is an essential trace element crucial for various physiological functions.
• Understanding selenium's interaction with milk components is vital for fortifying dairy products.
• Milk composition varies between species (e.g., goat, cow) and processing conditions.

Purpose of the Study:

• To investigate the binding of selenium (specifically selenite) to different milk fractions (cream, whey, casein) from goats and cows.
• To determine how incubation time, temperature, and pH affect selenium's association with milk proteins.
• To characterize the molecular weight of selenium-bound components in milk whey.

Main Methods:

• Raw goat and cow milk were incubated with sodium selenite (selenium-75).
• Samples were fractionated into cream, whey, and casein using centrifugation and acid precipitation.
• Whey fractions were analyzed using Sephadex gel filtration chromatography.
• pH was manipulated using lactic acid, and bacterial inhibitors were employed.

Main Results:

• In non-curdled milk (up to 6h incubation), most selenium-75 was found in the whey fraction.
• Curdling of milk (24h incubation or acidification) caused a significant shift of selenium-75 to the casein fraction.
• Selenium-75 in whey fractions primarily eluted in low molecular weight fractions, indicating minimal protein binding under non-curdling conditions.
• Selenium binding to casein increased substantially as milk pH dropped below 6.0.

Conclusions:

• Selenium (selenite) does not readily bind to milk proteins at normal pH.
• Milk acidification and subsequent curdling significantly enhance the binding of selenite to casein.
• The binding behavior suggests that selenium fortification in dairy products may be more effective under conditions that promote casein interaction.