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Robert E. Thomas
Information Specialist
573-882-2480
ThomasR@missouri.edu
Published: May 8, 2007
Story Source: Robert Marshall, 573-882-7355
row of store’s dairy case to avoid off-flavor, says MU prof
COLUMBIA, Mo. - If you're looking for milk in the supermarket that doesn't have that off-flavor similar to the odor of wet cardboard, reach back into the dim recesses of dairy case, said a University of Missouri food science professor.
"Get it from the dark," Robert Marshall advises consumers. "Definitely don't get the front row."
That's because fluorescent lights illuminating the front of dairy cases create an oxidized off-flavor in milk that some people call burnt, he said. The closer the milk container is placed to the lights and the longer it stays there, the greater the chance of an off-flavor.
Most consumers only check the code date to make sure the milk is fresh, but in most cases fresh milk will last well beyond the printed code date, Marshall said. Consumers should also check the location of the milk container in the dairy case.
"Milk stored within a few inches of fluorescent light in translucent containers usually has a detectable oxidized flavor within two to four hours and a distinct off-flavor within 12 hours," he said.
The clearer the container, the easier it is for milk to develop an off-flavor due to oxidation. Clear glass lets in the most light and then the translucent plastic jug, he said. Opaque paper board cartons generally do not have this problem.
In addition to causing an off-flavor, the wavelengths of the fluorescent light inactivate riboflavin, which is vitamin B2, and ascorbic acid, which is vitamin C, Marshall said.
The lights cause greater off-flavor in skim milk than in whole milk because the fat in the milk tends to block out the damaging wavelengths of light.
"In a supermarket, the milk in the front rows and lights can sometimes be only four inches apart, and you get very high exposure and rapid development of the off-flavor. If they are a foot apart or two feet apart, you get a lot less light hitting the surface of the package, so you get a lot slower development," he said.
The off-flavor can be avoided by shielding the milk with an orange dye in the plastic containers or by placing orange shields on the fluorescent light bulbs, Marshall said.
The degree of off-flavor may also be affected by the amount of copper in the milk. Milk contains small amounts of copper which acts as a catalyst.
Another factor is when the milk is stocked. If it is stocked during the night when not many people are buying, you have a greater chance of getting oxidized milk the next day.
The oxidation of the milk has little effect on its nutritional value and is not related to bacteria, Marshall said.
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| Fluorescent lights that illuminate supermarket dairy cases can oxidize milk, depending on the amount of exposure, and cause off-flavor and inactivate some vitamins in milk, according to research by Robert Marshall, University of Missouri food science professor. |
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| Robert Marshall, University of Missouri food science professor, inspects milk in his lab on campus. Marshall says to get milk from the back of the dairy case to avoid the off-flavor from oxidized milk. |
