Heating Process in Pasteurization and not in Sterilization Decreases the Iodine Concentration of Milk

Iodine is a vital component of the thyroid hormones and is required for normal growth, development, and tissue metabolism in humans and animals.

This study for the first time compares the effects of heating during pasteurization and sterilization on the iodine concentration of milk for an adequate provision of dietary iodine.

This study was carried out on multiparous Holstein Friesian lactating cows. Thirty Holstein dairy cows were fed with a diet containing 10 mg of potassium iodide (KI) per kilogram dry matter of diet. Milk samples were obtained on days 4 and 2 before and again on days 2, 4, 6, and 8 after the inclusion of KI into the total mixed ration diet of the dairy cows. The milk samples were sterilized using ultra-high temperature, following which the effect of the heating process during sterilization on the cows' iodine concentration was compared to that in the only previous documented study from Iran in which milk supplementation with KI was the same as ours. Milk in that study was pasteurized via the high-temperature short-time method, a method which involves temperatures in excess of 73°C for durations longer than 15 seconds.

The inclusion of KI in the diet of the dairy cows in these 2 separate experiments increased their milk iodine levels. Pasteurization decreased the iodine content of the milk (P < 0.05), while no significant difference was observed in the iodine concentration of the sterilized milk.

The present study showed that the iodine concentration is not decreased during the heating process in sterilization, indicating that supplemented sterilized milk could be a good alternative vehicle for dietary iodine in the prevention of iodine deficiency.