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Milk in the front row in local grocery stores isn't up to
snuff, says food science Professor Robert Marshall.
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Milk
in the Dark
By Robert E. Thomas
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 the dairy case, says a University
of Missouri food science
professor.
“Get it from the dark,” Robert
Marshall advises consumers. “Definitely don't get it from
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 says. 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 says.
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
says. 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
says.
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 says.
Marshall says 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.
The degree of off-flavor may also be affected
by the amount of copper in the milk. Milk contains small amounts
of copper that 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
says.
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Last Update:
November 15, 2007
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