Eating every day, there will always be some strange things, such as:
There is a black film on the yolk of the boiled egg;
Purple potatoes turn blue after cooking;
Purple rice actually faded after washing;
The sauce beef glows green after cutting...
Is this buying counterfeits, or is it encountering food spoilage? Could it be that there are villains who want to murder Yuan?
Today we will explain these "strange things" related to color.
(Source: Network)
Egg whites contain a lot of protein, and some proteins contain sulfur.
These sulfur-containing proteins have a characteristic, usually quite normal, but if heated for too long, the sulfur inside will be heated to "run out".
After the sulfur runs out, it first encounters hydrogen and combines it into "hydrogen sulfide". "Hydrogen sulfide" then runs, running to the place where the yolk and the egg white meet, and happens to encounter the "iron" contained in the yolk.
The two are very close, and when they are combined, they form "ferrous sulfide". "Ferrous sulfide" is gray-green, so the egg yolk has a "green film".
Although ferrous sulfide is not a good color, it is non-toxic and harmless in itself, and does not affect the absorption of proteins, and the amount generated is very small.
So you can eat with confidence.
(Source: soogif)
Purple potatoes are purple because they contain anthocyanins.
Anthocyanins are a natural water-soluble pigment and a "mischievous ghost" who loves to change color.
When the pH is different, it changes to multiple colors.
Red or purple red at pH 2.0 to 5.0;
Light blue-purple or blue at pH 6.0 to 7.0;
pH 8.0 became green again.[1]
Purple potatoes turn green, which is a trick of anthocyanins.
Because the water in some areas is weakly alkaline, when encountering such water, anthocyanins turn green.
When fried purple cabbage, vinegar turns red, which is a similar principle.
The colored sweet potato can still be eaten, but under alkaline conditions, the preservation rate of anthocyanins will be reduced, that is, the nutrients of anthocyanins that are "eaten" will become less.
If you feel sorry, you can add vinegar or lemon juice to the water in advance [2].
Purple rice is rich in anthocyanins, anthocyanins are water-soluble natural pigments, purple rice in the process of washing, the anthocyanins in it run out of the cells, the water is dyed purple.
Washed black beans and black sesame seeds do not fade, because the black pigment is anthocyanins.
Anthocyanins are the products of the binding of anthocyanins and sugars with glycoside bonds, and the stability is higher than that of anthocyanins.
Moreover, the cell structure of black beans and black sesame seeds is more compact, the "door" is more stringent, and the anthocyanins are not easy to run out.
Cut beef, the cut surface glows green, even a bit like a rainbow. Is this the meat spoiled, or what additives are mixed in?
Not really.
On some of the surfaces of striated, lumpy muscles, or cooked meat products, there may indeed be some spots.
The color of the spots is mainly green, yellow, and orange-red, and there is a kind of "fluorescent sense" of the rainbow, so it is called "rainbow color spots".
This is not rotten flesh, but a kind of "optical diffraction" of physics.
Because there are a lot of muscle fibers on the beef, there are coarse filaments, filaments, and horizontal stripes, they are uneven, and when the light hits these muscle fibers, it produces different diffraction patterns, which also makes the meat have a "rainbow" [3].
Nor does this mean that there is a problem with the quality of the beef. Beef can be eaten with confidence.
However, microorganisms do cause beef to turn green or fluoresce.
Want to distinguish which beef is normal and which are problematic? See table [3] below.
The world is strange, food is also, encounter things that do not understand, do not panic ~ welcome to ask the brother at any time.
Review expert: Cloud has no heart
Well-known science expert, doctor of food engineering
bibliography
Cheng Cheng, Liu Chao, He Wei, Zhou Yao, Wang Zheng. Stability and antioxidant properties of anthocyanins in purple sweet potato[J]. Chinese Journal of Nutrition, 2011, 33(3): 291-295.
Tian Xiqiang, Dong Yanping, Ma Songyan, Liu Xuyang. Stability and antioxidant properties of anthocyanins in purple potato[J].Food Industry, 2014, 35(8): 49-51.
Ji Yanfeng. Research on the control technology of rainbow stains in beef products[D]. Nanjing:Nanjing Agricultural University, 2007.
Author: Zhao Yanan | Editors: Zhao Yanan, Wu Wei, Ye Zhengxing
Typesetting: Han Ningning | Proofreader: Wu Yihe
Operations: Li Yongmin | Coordinator: Wu Wei