People eat in rivers and lakes, always encounter some strange things, such as:
Eating boiled eggs, I found that there was a black film on the yolk;
Eat boiled purple sweet potatoes, pick them up and find that the purple sweet potatoes have turned green;
Rinse the purple rice, after not washing a few times, it actually faded;
Eat the sauce beef, cut it and find that the beef is glowing green...
Is this buying a fake and shoddy product, or has it encountered food spoilage, could it be that there is a villain who wants to murder Xuan?
Today we will explain these "strange things" related to color.
(Source: Internet)
Don't make a fuss, it's just an egg that has been boiled for too long, a joke with you.
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 "run out" by the heat.
After the sulfur ran out, it first encountered hydrogen and combined it into "hydrogen sulfide".
"Hydrogen sulfide" then ran, ran to the place where the yolk and egg white combined, and happened to encounter the "iron" contained in the egg yolk. The two were very close and combined, forming "ferrous sulfide".
"Ferrous sulfide" is gray-green, so the yolk has a "black film".
Although the color of ferrous sulfide is not beautiful, it is non-toxic and harmless in itself, and does not affect the absorption of protein, and the amount produced is very small. So you can eat with confidence.
If you don't like it, just don't cook it too long!
"It is said that purple sweet potatoes are healthy, but why did the purple sweet potatoes I boiled become green, could it be that I bought black heart purple potatoes?"
Relax, this is normal, there is no problem with purple potatoes, and there is no problem with selling purple potatoes.
The reason why purple sweet potatoes are purple is because they contain anthocyanins, which are a natural water-soluble pigment and a "mischievous ghost" who loves to change color. When the pH is different, it will become a variety of colors, such as red or purple red at pH 2.0~5.0; pH 6.0~7.0 is light blue-purple or blue; pH 8.0 becomes green [1].
Purple sweet potatoes turning green is a trick of anthocyanins, because most of the northern water is weakly alkaline, and when encountering such water, anthocyanins turn green. The same is true when stir-fried with vinegar and turning red.
Therefore, the discolored sweet potatoes can still be eaten, but under alkaline conditions, the preservation rate of anthocyanins will be reduced, that is, the anthocyanins "eaten" will become less of this nutrient, if you feel a pity, you can add some vinegar or lemon juice to the water in advance [2].
(Source: Internet)
Why does the purple rice bought at home fade as soon as it is washed, but the black beans and black sesame seeds do not fall off, this time it is encountered "fake purple rice", right?
Not really.
Whether it is purple rice, black beans, or black sesame, the reason why it is purple or black is because it contains purple-red or black pigments such as anthocyanins and anthocyanins.
As mentioned earlier, anthocyanins are water-soluble natural pigments, and during the washing process of purple rice, the anthocyanins in it run out of the cells and dye the water purple.
The black pigment in black beans and black sesame seeds is anthocyanins. Anthocyanins are the product of anthocyanins and sugar bonding with glycosidic bonds, and the stability is higher than that of anthocyanins. Moreover, the structure of black beans and black sesame cells is closer, the "door" is tighter, and anthocyanins are not easy to run out, so cleaning is not easy to fade, but if soaked for a long time, it will still fade.
(Source: Internet)
At noon, I bought a piece of sauce beef and took everything home, and found that the cut surface was green, even a bit like a rainbow. Is this bacteria, or is it mixed with some additives?
It may not be.
On some streaked, lumpy muscle surfaces, or the surface of cooked meat products, there may indeed be some spots, the color of the spots is mainly green, yellow, orange-red, there is a rainbow "fluorescent sense", so it is called "rainbow spots".
This is not meat rotting and deterioration, but an "optical diffraction" of physics. It is because there are a lot of muscle fibers on beef, there are thick silks, fine filament, horizontal lines, they are uneven, when the light hits these muscle fibers, it produces different diffraction patterns, which makes the meat have a "rainbow" [3].
This does not mean that the quality of the beef is not good, let alone that the quality is questionable. Beef can be eaten with confidence.
Of course, microorganisms do cause beef to spoil and turn green, or fluoresce. How to distinguish between normal and problematic? You can refer to the table below [3].
The difference between rainbow-colored flesh and spoiled green flesh and fluorescent-colored flesh
Reviewer: Yun Wuxin
Well-known science expert, doctor of food engineering