Many friends who often cook have experience. If fresh garlic is not used up after being chopped up, it is likely to turn green. Also, if it rehydrated using dehydrated garlic flakes or dehydrated garlic granules or garlic powder, it will slowly turn green after standing for a period of time. However, dehydrated granulated garlic or dehydrated garlic powder processed from frozen garlic immediately appear green after rehydration. What is the reason?
The phenomenon of garlic turning green after a long time is called “ garlic greening" in terms of food science. The study of green change was only just started in the 1950s. At first, scientists found that garlic does not turn green under any circumstances. If you want garlic to turn green, you must have some strict triggering conditions:
Garlic in a broken state or after acid treatment is more likely to turn green, and intact garlic is less likely to turn green.If garlic is refrigerated at 0 - 4 ℃, it will turn green very easily, and the garlic stored at normal temperature will not turn green obviously.
Scientists are gradually focusing their attention on a chemical substance. This chemical is called " propenyl cysteine sulfoxide" ( pictured below ), or PECSO for short. Scientists have found that the content of this substance has increased significantly in all garlic that produces green color.
This only proves the correlation between PECSO and green change. How can we prove the causal relationship? Scientists added PECSO extracted from onions to the garlic paste that did not turn green. Magical things happened, the garlic paste quickly turned green. Obviously, PECSO is the reason why garlic turns green.
But the problem is that PECSO itself has no color. Why does this colorless substance cause garlic to turn green?
After more in-depth research, scientists finally outlined the matter: it was the result of a very complex set of enzymatic reactions. PECSO was catalyzed by garlic enzyme to form pigment intermediate, which reacted with pyruvic acid, amino acid and allicin in garlic to form yellow pigment and blue pigment. Taken together, what we see is green.
At this point, there is still an initial problem that has not been solved. Maybe you also want to ask.
“How did PECSO in garlic come into being? Why does the content of this substance increase after shredding, acid treatment or cold storage? 」
This is about to mention another enzyme, its name is γ -glutamyltranspeptidase. It is abundant in garlic and can catalyze the hydrolysis of certain polypeptide in garlic to PECSO.
Garlic itself is made up of cells, and the polypeptide and this enzyme cannot meet at ordinary times, but if it is chopped up, the enzyme and substrate will combine and the reaction speed will certainly be much faster. Acid treatment can increase the permeability of cell membrane, and also can “release" the enzyme from the cell.
So, what about low temperature?
It turns out that garlic will enter a “dormant mode" at room temperature, when the activity of γ -glutamyltranspeptidase is very low. Once in the low temperature environment, garlic dormancy will be broken and γ -glutamyltranspeptidase will be activated one by one, thus opening the first lock of the green transformation reaction.
This explains why dehydrated garlic flakes, dehydrated garlic granules and dehydrated garlic powder made by cold storage garlic can appear green immediately after rehydration.
Here, we finally depicted a simple outline of the process of garlic green transformation. There are many more complicated and subtle details in it, waiting for scientists to continue to explore.
Garlic turns green without damaging health, but garlic minced or dehydrated garlic powder cannot be stored for a long time after rehydration, because qualitative changes will occur. If you find abnormal taste, whether the color changes or not, you can only put it in the trash can.
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