作者:DR. RUSSELL MOUL
Compilation: Muggle
图片来源：Natalia Lisovskaya/Shutterstock.
Contrary to popular belief, bright red meat is not discolored by blood, and the mere color itself does not mean that the meat has been "broken". Is grey steak meat safe to cook? Or should it be thrown away?
Have you ever wondered why that red-looking steak you bought a day or two ago is now gray in the fridge? For those who eat meat, you might think that the color of a product is an absolutely valid way to assess its freshness and quality – the redder the better, right? Well, color isn't always a reliable indicator because supermarkets have tricks up their sleeve to superficially enhance its color. So are gray stripes naturally bad for you?
Where does the red in "red meat" come from?
Red meat, sometimes referred to as "dark meat," derives its color from myoglobin, a protein that binds oxygen to muscle cells.
Myoglobin itself is purplish-brown, so freshly slaughtered meat will look duller in color. But when myoglobin is exposed to oxygen, it forms a complex oxidized myoglobin that becomes lighter and makes the meat richer and redder in color, and we can associate it with healthy foods – albeit only as a "link".
So, probably contrary to what you believe, when you order a raw steak, the red liquid on your plate is not blood, but water and myoglobin.
Over time, the presence of oxygen will eventually turn the meat grayish-brown. This is due to the continuous oxidation of myoglobin, which becomes methemoglobin. The NSW Food Authority explains that the larger surface area means that ground meat is more likely to turn grey than whole cuts. No matter what you think, this doesn't mean that meat is inedible or spoiled (although you should still be cautious).
If your refrigerated steak has just turned gray, it's probably due to the oxygen in the fridge rather than a sign that it's starting to rot. However, since this process usually takes a few days to complete, it's still worth checking the meat before cooking it (especially if it smells and/or slimy), as the USDA claims that if all the meat is gray or brown, it could be a sign that the meat is starting to spoil.
When you buy a steak from the store, you may find that the steak in the bag is purple and darker in color. This is because meat needs oxygen to turn red, and vacuum-sealed packaging prevents oxidation from occurring.
This may make you wonder why some store-bought meat is still bright red, even though it is sealed in plastic. This is usually because supermarkets often use specially designed plastic, which is slightly porous. Even though the holes in the plastic are too small to allow the liquid to flow out, they still allow air to get in and out.
Sources:
https://www.iflscience.com/why-does-fresh-steak-turn-gray-and-is-it-safe-to-eat-73186
作者:DR. RUSSELL MOUL
Russell is a science writer at IFLScience with a PhD in the history of science, medicine, and technology.