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    Home > Biochemistry News > Biotechnology News > Discolored fruits and vegetables? It turns out to be a natural "magic"

    Discolored fruits and vegetables? It turns out to be a natural "magic"

    • Last Update: 2020-06-19
    • Source: Internet
    • Author: User
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    Natural food, always colorful, light yellow and dark green, let people have an appetiteStrawberries should be red, purple potatoes should be purple, leafy vegetables should be green, black rice should be black < br / > however, there are also such situationsRecently, a friend asked: my purple potato, the boiled water has turned green! What's the matter? I'm afraid I can't eat it! < br / > another expert called: the purple rice I bought will fade as soon as I wash itIs it dyed purple? < br / > a neighbor also asked: the yam I bought is obviously whiteHow does the surface appear blue and purple after steaming? Do you look at the photos? Is it a little scary? < br / > in fact, this kind of food discoloration is not uncommonFor example, purple cabbage becomes dark grey blue after being fried, green leafy vegetables become olive green after being cold mixed, and the beautiful pink color of tomato noodles disappears after being put on for a long timeSome people are worried because of artificial dyeingThere are also concerns because of chemical fertilizers and pesticidesThere are also concerns about food adulteration< br / > in fact, the discoloration of these foods just shows the fact that the colors of these foods are purely natural, not the result of artificial dyeing, and have nothing to do with chemical fertilizers and pesticides< br / > there are four kinds of the most common natural pigments < br / > the pigments in nature do not exist for human needsThey are the characteristics of fresh natural food, but they are not intended to last foreverIn the process of cooking, processing and storage, they are often quite delicate and changeable< br / > compared with artificial pigment, it is much more "skin solid"Because in the initial development and selection of artificial pigments, the basic requirements are strong coloring power and good stabilityIf it is easy to fade and change color, it will be eliminated< br / > among all kinds of food, there are four kinds of natural pigments Tetrapyrrole pigment: it includes heme in meat and chlorophyll in green vegetables They are good at capturing and transmitting light energy, and also like to "trap" some metal ions < br / > 2 Carotenoid: a series of pigments from yellow to orange to red, such as carotene in carrot, orange, mango, pumpkin and other foods, lycopene in watermelon, tomato and blood orange What lutein, zeaxanthin, citrus flavin, capsanthin, astaxanthin and so on all belong to this category < br / > 3 Polyphenol pigment: it includes anthocyanin and other flavonoids, such as flavonoids < br / > anthocyanins are a big family, but their styles are the same, from purplish red to purple to blue purple to purple black < br / > most of the blue purple and purple black food colors are due to anthocyanins, such as purple potato, purple cabbage, purple onion, blueberry, mulberry, purple black cherry, black peanut, black rice, black soybean, black corn, etc < br / > flavonoids are colorless to yellow, usually lighter and low-key Beet pigment: including beet red pigment and beet yellow pigment Beet red element is not rare, red beet head, cowhide vegetable (beet for leaves), red amaranth, red heart pitaya that kind of rose red color is brought by beet red element < br / > these four kinds of pigments have the ability to fade, change color or fade, but their temperaments are different < br / > food discoloration is due to pigment dissolution caused by cleaning < br / > first, let's talk about many people's complaints about discoloration In fact, the reason why most natural foods lose color after washing is that the pigment is dissolved Washing with water is easy to fade, because the pigment in food is just soluble in water For example, polyphenol pigments and beet pigments are water-soluble pigments When they are dissolved in water, they will lose color < br / > we all have the experience that strawberries, mulberries, bayberry, red dragon fruits will fade when washed This is because the cells of these fruits are delicate When they are washed with water, the cells are damaged by external forces The pigment that originally stayed in the plant vacuole quietly runs into the water < br / > but you may say that tomatoes are also delicate Why can't they dissolve red when they are cut and washed? This is because lycopene is a fat soluble pigment, which is not soluble in water at all, so it will not fade when washed < br / > however, since it is fat soluble, if it is washed with grease, it will dissolve Therefore, the oil will turn red after frying tomatoes and yellow after frying carrots The chef just uses this principle to stir fry tomato sauce with hot oil to add red color to the tomato juice vegetables < br / > you may also say, but my black beans didn't fade when they were washed! Why does black rice fade? Here is another important factor: can cells contact water immediately < br / > for seed food, such as beans, seed coat and other outer tissues, the cell structure is relatively close, so the cells will not absorb water temporarily after a short time of washing, so the pigment in them will not escape < br / > however, if the seeds are soaked for a long time, they think that the chance of germination has arrived, and the outer layer will gradually absorb water At this time, anthocyanins will slowly dissolve When soaking in hot water, the speed of water absorption will be faster, and the speed of pigment dissolution will be faster < br / > there is a big difference in the density of outer layer cells among different varieties of seeds < br / > some varieties fade quickly after soaking, such as purple red glutinous rice; others need to soak for more than an hour to see obvious fading, such as some black rice; others are slower, such as black soybean and red bean But in any case, as long as you insist on soaking, the anthocyanin pigments will be bubble out < br / > foods containing anthocyanin and chlorophyll are prone to discoloration < br / > besides, many people are confused about the discoloration There are mainly anthocyanins and chlorophyll in the discoloration < br / > anthocyanin is a chameleon It turns bright and delicate pink or purplish red in case of acid, green or blue purple in case of alkali, and it can turn into a very deep color in case of some metal ions, such as dark green, dark brown, gray black, etc., which is really a little scary < br / > for example, the water is green after the purple potato is boiled, which only means that the water for cooking purple potato is weak alkaline water (hard water), which causes the anthocyanin to change color There is no poison in it Don't be afraid And cold purple cabbage with vinegar becomes particularly red and beautiful, just because the acid of vinegar plays a role in discoloration < br / > sometimes, just when the pigment dissolves, it seems to have changed color For example, after soaking black rice, black peanuts, black soybeans and other foods for several hours, you will find that the color is not black at all, but dark red or purplish red This is because the anthocyanidins of others are not black, OK Just because the color is too thick, the surface looks black Dilute them to show their true colors < br / > chlorophyll is not that good It will only turn dark yellow green (olive green) when it meets acid This is because the magnesium ion in chlorophyll leaves the post without permission with the help of hydrogen ion, which causes the color change < br / > so the color of old vinegar mixed with spinach is not so attractive However, if you add more salt (sodium ion) to the vegetables, or use lime to soak (calcium ion), the color will look better If we add some copper ions, the color will be more green, and it will last for a long time This is why some dried zongzi leaves can keep green all the year round < br / > natural pigments are not stable and easy to fade < br / > in addition to fading and discoloration, there are many natural foods with fading phenomenon As mentioned above, the chemical properties of natural pigments are not stable and can degrade due to heating or oxidation < br / > anthocyanin is the most unstable pigment It will fade gradually when heated for a long time The higher the temperature and the longer the time, the more difficult it is to preserve the color So far, there is no way to keep strawberry, cherry, mulberry, Bayberry and other foods in beautiful color after cooking The color of the fruit itself soon became ugly So, no matter which country you are in, the red and colorful canned cherries you see on the birthday cake are actually dyed < br / > carotene and lycopene, which seem stable and honest, will also fade If you put dried tomato powder, vegetable noodles mixed with carrot juice and other products in the supermarket, you will find that after a few months, their color will become lighter and lighter, and eventually completely fade < br / > because these pigments contain many unsaturated bonds, oxygen will not let them go Of course, if you can keep it away from light and oxygen at low temperature, the color will last a little longer < br / > there is no need to worry about the color change of food from colorless to colorless Many white foods contain precursors of polyphenol pigments They are colorless in themselves, but they hydrolyze during cooking or processing, or change to colored anthocyanins < br / > for example, yam will turn purple after steaming, which belongs to the color change of food from colorless to colored Peaches are red in the center after cooking, and lotus roots are blue and purple after steaming This situation is non-toxic and harmless It's good to eat at ease < br / > there are also some flavonoids in light food, which will change into chalcone structure with obvious color under alkaline condition For example, apples and onions turn yellow after cooking, steamed bread turns yellow after putting alkali, zongzi turns yellow after putting alkali water, which is caused by this principle Basic conditions can destroy some B vitamins, but discoloration is not harmful to people at all < br / > so, almost all the discoloration, discoloration and fading of food in daily life are caused by natural pigments! < br / > if you are always suspicious of food, you will not only make yourself too nervous, but also wrongly the farmers who produce them, and also fail to live up to a lot of natural good food
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