Enzymatic release of sequestered cows' milk fluoride for analysis by the hexamethyldisiloxane microdiffusion method

Area of Science:

• Environmental Science
• Analytical Chemistry
• Food Science

Background:

• Fluoride levels in drinking water can vary significantly.
• Cow's milk composition can be influenced by environmental factors, including water fluoride content.
• Accurate measurement of fluoride in milk is important for assessing dietary intake and potential health impacts.

Purpose of the Study:

• To determine the concentrations of diffusible and total fluoride in cow's milk.
• To evaluate different methods for measuring total fluoride in milk, including open ashing and enzymatic digestion.
• To investigate the nature of fluoride in milk, distinguishing between inorganic and bound forms.

Main Methods:

• Fluoride electrode used for quantification.
• Hexamethyldisiloxane microdiffusion for diffusible fluoride.
• Open ashing (with magnesium nitrate/acetate) and proteolytic enzyme digestion for total fluoride.
• Comparison of different sample preparation techniques.

Main Results:

• Diffusible fluoride concentrations ranged from 0.024 to 0.28 µg/mL.
• Total fluoride concentrations ranged from 0.05 to 0.31 µg/mL.
• Enzymatic digestion effectively measured total fluoride, indicating it's inorganic and sequestered in milk proteins.

Conclusions:

• All fluoride in cow's milk is inorganic.
• Bound fluoride is physically or chemically associated with milk proteins.
• The proposed method using enzymatic digestion is convenient for total fluoride analysis in milk.