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Virginia Tech researchers iron out unusual flavors in milk

June 21, 2016

Small containers of milk with red tops contained in ice.
Virginia Tech researchers have found that iron can contribute to off flavors in milk.

Nothing is quite as satisfying as a tall, cold glass of milk, but odd flavors can be off-putting to consumers.

Researchers at Virginia Tech have traced what could be a source of unusual flavors in milk’s taste profile  — too much iron in cows’ water sources.  The effect of too much iron is "bitter," "fishy," or "paint"-like off-flavors that are not typical of fresh milk  — or compatible with cereal or cookies — and can cause consumer concern about drinking milk. 

A recent study published in the Journal of Dairy Science shows that iron in bovine water sources was causing oxidized flavors, degrading milk fats and proteins, and contributing to general poor stability of milk products. High iron content in water also decreases the cow’s ability to efficiently process some types of nutrients, which decreases production levels and makes the animals susceptible to a host of other health issues, including mastitis and other bacterial infections. Nutritionally too much iron also decreases the cow’s ability to digest certain nutrients.  

“What we found is that when iron was present in the water, or we added iron, we got a flavor profile that was far removed from the subtly sweet, creamy natural flavor of fresh milk,” said Susan Duncan, professor of food science and technology and one of the lead authors in the iron study. She is also the associate director of the Virginia Agricultural Experiment Station at Virginia Tech.

The work was done by a collaborative research effort in the departments of Dairy Science, Food Science and Technology, and Biochemistry in the College of Agriculture and Life Sciences, and Civil and Environmental Engineering in the College of Engineering.

“While dairy farmers may not see the effects of iron in their milk composition immediately, over time this could pose a problem for dairy processors who might notice a decline in quality and sales for no apparent reason,” said Duncan. "We saw more milk protein fragments when cows were consuming more iron in their water. This can cause a problem for making other dairy products, like yogurt or cheese, too."

The research team found that the “off” flavors in the milk are caused by the degradation of caseins – or proteins – in the milk, which can contribute bitter tastes and a drying sensation in the mouth, as well as the oxidization of lipids – or fats – that occurs when excess iron is present in water sources. Casein degradation can lead to bitter and astringent notes. Fat oxidation can lead to painty and fishy notes. 

More than 80 percent of milk is water, and dairy cows drink about 100 liters of water each day to produce milk.

The amount of iron needed to contaminate milk was as low as 2 milligrams per liter.

“This study helped to uncover what could be a new baseline recommendation for producers who will likely want to test their water sources and collection and transportation equipment to ensure the iron levels are not too high from any of their sources,” said Aili Wang of Tianjin, China, who is first author on the paper and a post-doc in food science and technology.

Sources of iron may be  naturally occurring in the groundwater from the weathering of  iron- and manganese-bearing minerals and rocks. Nearby industrial run, acid-mine drainage, sewage, and landfill leachate that may find their way into water sources may also  contribute  to high iron and manganese levels on  dairy farms.

There are naturally occurring areas of high iron content in the commonwealth as well. These areas are made up primarily of granite, shale, and sandstone. The  disintegration and decomposition of the granite bedrock allows the granular material formation that serves as aquifers  to supply water to shallow  wells. These waters frequently contain large amounts of iron.

The multidisciplinary project was funded in part by the Virginia Tech Pratt Animal Nutrition Program, Virginia Agricultural Experiment Station, the Hatch Program of the National Institute of Food and Agriculture, U.S. Department of Agriculture, and the Virginia Tech Water INTERface Interdisciplinary Graduate Education Program. Other collaborators include Dennis Dean, University Distinguished Professor of Biochemistry and Fralin Life Science Institute-associated faculty, and Valerie Cash and Keith Ray of the Virginia Tech Mass Spectrometry Laboratory.

Written by Amy Loeffler

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