It has been reported that black rice dyeing and medlar dyeing have made everyone panic, so that when businesses sell products, they solemnly mark that they are not dyed food!
Washed purple rice water
Must the faded food be dyed?
Now the variety of vegetables, fruits and grains is increasingly rich. Consumers are often afraid of being dyed in the face of new colors of food. On the other hand, news such as dyed sesame seeds and dyed oranges often burst out. How to judge which fade is normal and which fade is abnormal? This should start from different kinds of plant pigments.
Red, orange and yellow that are not easy to fade -- carotenoids
Carotenoids are a kind of natural pigments widely distributed in various plants. Now there are more than 600 kinds of carotenoids identified. The common carotenoids include & alpha; - carotene, - beta; - carotene and lutein in carrots, pumpkins, sweet potatoes and dark green vegetables; lycopene in tomatoes and red watermelon; zeaxanthin in corn. Rutaceae plants such as lemon, orange, orange and grapefruit also contain a lot of carotenoids. In fact, some animals also have carotenoids, such as astaxanthin, which turns red when cooked in shrimp and crab. (for more information about carrots, please see: will carrots be poisoned by vitamin A if they eat too much? Must carrots be fried with a lot of oil?)
Some carotenoids are involved in photosynthesis, a very important physiological process of green plants. Beta; carotene and lutein in chloroplast play the role of 'light receiver' in photosynthesis. These pigment molecules absorb solar light energy, and then transmit these light energy to the chlorophyll molecules in the center. After conversion, these energy can be fixed in the organic compounds synthesized by plants and used by plants.
One of the common characteristics of carotenoids is that they are easy to dissolve in oil but not in water, so unless the skin is damaged, boiled or squeezed into juice, simple washing of carotenoids rich red and orange vegetables and fruits should not appear discoloration. This is the opposite of the water-soluble anthocyanins below.
Red, blue and purple, which are easy to fade and change color -- anthocyanins
The colorful flowers in nature are the most beautiful scenery, and we can see these beautiful flowers largely due to the anthocyanin in the vacuole of petal cells. Anthocyanins are often combined with different monosaccharides to form various types of anthocyanins. Anthocyanin has a special property that its color can change with the pH of the solution it is in. When the solution becomes acidic, the color of anthocyanins will tend to red; when the solution becomes alkaline, the color of anthocyanins will tend to blue. It is precisely because of the different acidity of vacuoles in plant cells, all kinds of anthocyanins will change color, making the petals look good.
The common anthocyanin rich fruit and vegetable parts can be used as acid and alkali indicators after juicing. Of course, the colors of different varieties will be different, so it is only for reference.
In addition to petals, anthocyanins are also found in various tissues and organs of many plants. From the common purple cabbage, red onion, eggplant, black rice and black bean, to the novel purple carrot, purple potato, black peanut and laver flower, the ingredients rich in anthocyanin are easy to fade and are often suspected to be dyed.
The pickles made of poplars, also called water radishes, are also easy to fade, because the pigment in red radish is anthocyanins.
In fact, it is very normal for the ingredients rich in anthocyanins to fade, because unlike carotenoids, anthocyanins are water-soluble. If you are not sure, you can also use white vinegar to test, the purple black anthocyanin solution will turn red after meeting white vinegar. For example, purple sweet potato and purple cabbage are easy to change color in cooking. If you cook purple sweet potato porridge with alkaline water, it will turn blue; if you use purple sweet potato as pastry, if you put baking soda, the paste will turn ugly green. (tip: use yeast instead of baking soda to ferment, or choose zihuai mountain, also known as yam to make pastry. ）At the same time, if you want to fry the purple cabbage color better, you can put a little white vinegar to keep the color bright.
Alternative red and black -- beet red and melanin
There is a kind of red plant pigment, which is not easy to fade the carotenoids, nor easy to fade and discolor the anthocyanins, that is easy to fade and excellent dyeing effect of beet red. There are two common vegetables and fruits rich in beet red, the red vegetable head used in Russian red vegetable soup and the Pitaya with red pulp. Beet red generally presents a beautiful purple red color, which is far less sensitive to acid and alkali than anthocyanin. If you eat too much, you will also change the color of urine. Therefore, if you eat red cabbage head or red pulp of pitaya, you don't need to panic.
The picture above shows the red dragon fruit, and the picture below shows the vegetable salad with the red vegetable root and the egg.
Although black ingredients are often associated with anthocyanins. But in fact, black ingredients don't always contain a lot of anthocyanins, such as black sesame and black fungus, which are hard to dissolve in water. Black sesame contains a small amount of anthocyanin at the same time, so it is normal to have a slight discoloration, and if a large amount of discoloration makes the seeds white, it is necessary to doubt whether they are dyed. Black agaric should not fade at all.
Why does food fade?
In our daily life, we often encounter some foods' discoloration 'when they are washed, but sometimes the same color of food does not discolor. There are two reasons for this.
One is the nature of the pigment itself. We know that different substances have different solubility in water. The natural anthocyanins in food have high conjugation system, acid and alkaline groups. They are polar molecules. According to the principle of "similar phase solubility", they are easily dissolved in polar solvents such as water and alcohol. The common structural feature of carotenoids is the long chain with nine double bonds, most of which are fat soluble molecules, which are difficult to fade when washed with water. Melanin is also insoluble in water.
There are many black foods, but they are black for different reasons.
On the other hand, consider whether the pigment in food is easy to be 'squeezed out'. As mentioned above, the anthocyanin molecule of purple potato is not only in the cell, but also in the cell wall. When such a situation occurs, even if you only need to hold the purple potato when eating, you will get purple. There are only anthocyanins in the peel, such as eggplant and blueberry. Although they will fade after a long time of soaking, they will not fade after normal washing and grasping. (for more information, please see: what's the matter with the discolored fruits and grains? Are the discolored black peanuts dyed?)
Conclusion:
With the continuous development of agriculture, the color of fruits and vegetables is becoming more and more rich. There are various kinds of new colors of food materials, some of which are easy to fade or change color, which is also very normal without panic. We can better enjoy the natural gifts and avoid buying dyed products by purchasing food materials from regular channels instead of those that are significantly lower than the market price and learning the principles behind plant pigments.