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. They're gray before you toss them in boiling water and then turn brilliant red or orange.
Cooking changes the protein in the shellfish.
A similar phenomenon destroys most bacteria. 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. 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.