Hot & cold bacteria
 Q: Why does fire kill bacteria but freezing
doesn't? For example, you freeze a piece of raw
meat, let it thaw, and eat it. You may get sick.
But if you heat it high enough, you can usually
kill the bacteria.
Escherichia coli
thriving happily in the warm human gut; the organisms cause diarrhea.
Photo courtesy of James A. Sullivan, Cells Alive © Used with permission
A: Think about lobsters and shrimp. They're gray
before you toss them in boiling water and then turn
brilliant red or orange. What happens? Cooking
changes the protein in the shellfish.
A similar phenomenon destroys most bacteria.
Cooking alters protein structure so it doesn't
function as it should. Since proteins are involved in chemical processes essential for life, changing
its protein dooms the bacteria. On the other hand, freezing usually does not disrupt the structure,
says Gail Sullivan of the University of Virginia Health Science Center.
There are exceptions as you mention: some bacteria like more heat than others and some need
special measures so they don't die when frozen. Back in the 1960s, Thomas D. Brock of
University of Wisconsin-Madison was poking around in the hot springs of Yellowstone and found
some strange bacteria. That was back when biologists thought life couldn't tolerate high
temperatures. These bacteria, however, liked water close to boiling hot. They thrived and
reproduced.
Enough heat, however, can kill even heat-loving bacteria: Its protein eventually cooks.
Further Surfing:
In hot waters, The Why Files
Cells Alive by James A. Sullivan
Doneness versus safety, Food Safety and Inspection Service, USDA
|
