Why does mung bean soup turn red?
In fact, the mung bean soup I have seen since I was a child is going to change color. Throw mung beans into the boiling water pot, cover the pot and cook for a few minutes. The green mung bean clear soup is cooked, but the beans are still intact and not broken at all. My mother told me that this soup is particularly refreshing and needs to be drunk quickly, otherwise it will change color after a long time and the effect will be reduced.
Sure enough, after drinking this bowl of mung bean soup and opening the lid, you can see that the color of mung bean soup is not so green. After they are filled in, the color becomes darker and darker, from green to yellow, from yellow to orange, and from orange to red. Hotels in old Beijing and free mung bean soup in summer are all popular. Boiling mung bean porridge has a similar phenomenon.
In fact, the principle of turning red is very simple. It is the result of oxidative polymerization of phenols dissolved from mung bean skin in mung bean soup under the action of oxygen in the air. Therefore, cooking mung bean porridge with the lid open is easy to change color, while cooking mung bean porridge with pressure cooker is not easy to change color.
Because the effective component of mung bean for heatstroke prevention is mainly polyphenol antioxidants, it is very important to maintain its activity for the heatstroke prevention effect of mung bean.
What changes have been made in the nutrition of mung bean soup with different colors?
What is the difference between green soup and red soup in health care effect? Through the determination of antioxidant properties, it was found that the free radical scavenging ability of mung bean soup was closely related to the color. The green mung bean soup is much better, but the discolored mung bean soup is obviously worse.
Data analysis shows that there is a significant correlation between the color of bean soup and its antioxidant activity. Adding a small amount of salt and citric acid can improve the antioxidant effect, while boiling with alkali will greatly reduce the antioxidant effect.
Mung bean is rich in B vitamins, which is an important part of its summer-heat relieving characteristics and can make up for the nutritional loss when sweating. Alkali can seriously destroy many B vitamins. At the same time, the flavonoid antioxidant components in mung beans will be lost due to alkali addition, and the structure will change and the color will turn yellow. Therefore, it is best not to add alkali to cook mung bean porridge. If you want to make porridge sticky, consider adding a small amount of oatmeal or glutinous rice to "thicken".
Tips for preventing discoloration of mung bean soup
1. Boil with purified water.
So, will the cooked mung bean soup turn red? Actually, it's not. Our experiment proves that mung bean soup can be preserved for a long time without discoloration. The mystery of the problem lies in the different water used to cook beans.
Mung bean soup is boiled with tap water, mineral water, purified water and deionized water respectively. The results show that the color of deionized water is the greenest and remains unchanged for a long time. The color of the cooked mung bean soup changes the fastest, and it will obviously turn dark and red almost every minute when exposed to the air. It is obviously caused by the different water quality.
We adjusted the tap water to different pH values to cook mung bean soup, and found that the pH value can greatly affect the discoloration effect of the soup. Acidic tap water rarely changes color after boiling, while weakly alkaline tap water changes color very quickly after boiling. Tap water in the north is mostly alkaline water, so the boiled mung bean soup changes color very quickly, and obvious color changes can be seen within two minutes. But for deionized water, no matter what pH value, the color change is very small.
In this way, a simple method of boiling mung bean soup without discoloration is obtained-directly boiling it in pure water, no problem.
2. Add some vinegar when cooking.
If there is no pure water at home, it is not impossible to keep green by boiling mung bean soup with tap water. When cooking mung bean soup, just add half a spoonful of white vinegar or squeeze half a spoonful of lemon juice to keep mung bean soup in the air for a long time.
The key is, don't add too much, let alone make the water sour, just adjust pH 6.
When cooking, it is best to adjust the water first, and then cook the mung bean clear soup, so that it is not easy to change color. Even if it is stored for half an hour, it still looks good.
3. Cover the pot and cook quickly.
When cooking mung bean soup, cover the pot to minimize the contact area with oxygen and reduce oxidation. Moreover, the heating time of boiling water is shorter than that of cold water, and the oxidation is slightly less. Pressure cooker cooking has less contact with oxygen, which is beneficial to maintain the color of soup. However, as long as the soup is scooped out, it will soon change color.
Meanwhile, pay attention to the cooking time. When cooking mung bean soup every day, it is difficult for them to keep yellow-green because of the long cooking time and full contact with oxygen. It is advisable to take out the soup cooked in 10 minutes and drink it as soon as possible, because the bean soup at this time is green in color, and the dissolved substances are mainly the effective components in the bean skin, with the lowest oxidation degree and the strongest heat-clearing ability.
Don't throw away the remaining mung beans after taking out these soups. You can add boiling water and continue to cook it into mung bean paste, or you can add rice and cook it into mung bean porridge.
Do you want honey or sugar to cook mung bean soup?
If you add a lot of honey to mung bean soup, the soup will become dark, because honey contains many minerals, including iron ions. However, these metal ions often form "compounds" with polyphenols, and the colors are sauce color, black, brown, dark green and so on. This makes the soup dark. This is a normal phenomenon, non-toxic and harmless.
But this may affect the absorption of trace minerals in honey, but because of the small amount, it does not hinder the overall nutrition of the diet.
In addition, putting a lot of sugar or honey in the cooking process will prevent water from infiltrating into beans and affect the gelatinization process of starch. Sugar and honey are both ingredients that like water. On the one hand, they compete with starch for water, on the other hand, they prevent starch molecules from fully diffusing in water. Then, can I cook mung bean soup in an iron pan?
As we all know, traditional Chinese medicine can't be fried in an iron pan, and fruits can't be cooked in an iron pan. Among them, in addition to the fact that iron can catalyze the oxidative decomposition of various vitamins, there is another reason, that is, it is worried that iron will react with active ingredients such as polyphenols in medicinal materials and fruits, thus affecting the efficacy or color. With a casserole or ceramic pot, you wouldn't have these troubles. So is mung bean soup.
Flavonoids in mung bean skin may react with metal ions to form darker compounds. For example, adding honey to mung bean soup will produce a kind of black, and the same is true.
Although no toxic substances are produced in this reaction, it may interfere with the antioxidant effect of mung beans and hinder the absorption of metal ions. Therefore, when cooking mung bean soup, it is most inappropriate to use an iron pot, and it is most ideal to use a casserole.
When adding sugar, cook for a while or raise the cooking temperature.
Nutritional value of mung bean
Let's talk about mung bean clear soup first, and then talk about the basic nutritional value of mung beans.
The protein content of 1 mung bean is 20%, which is three times that of rice. protein is rich in lysine. Mung bean protein also binds to heavy metal ions, which is the source of its detoxification function. Both mung bean soup and mung bean sauce are healthy. You can't throw away beans just because you drink soup.
2 Mung bean starch has slow digestion and slow blood sugar rise, which is suitable for diabetics without diarrhea and indigestion. In addition, animal experiments have proved that mung bean starch is beneficial to control blood lipids. Therefore, patients with hyperlipidemia can often eat mung bean porridge and mung bean rice in summer.
The content of B vitamins and potassium in mung beans is high. Sweating in summer will lose a lot of sodium, which can be supplemented from various salty foods; But the lost potassium and B vitamins can be supplemented by mung bean soup. Drinking mung bean soup in summer can replenish water, quench thirst, clear heat and relieve annoyance, which is much better than drinking iced sweet drinks.
Mung bean skin is more nutritious than meat.
When cooking mung beans, many people throw away the skin; When making mung bean vermicelli and bean paste, it is traditional to discard not only the bean skin, but also the water used to cook beans. In fact, the real benefit of mung bean lies in its skin.
It was found that most of the active components in mung bean existed in the skin of mung bean, and the main components in the two cotyledons were protein and starch. Mung bean skin contains a lot of antioxidant components, such as flavonoids, tannins, saponins and so on. There are alkaloids, coumarin, coumarin, cardiac glycoside, and a lot of dietary fiber.
Studies have proved that the application of mung bean skin extract to rats can obviously reduce the damage to their health caused by extreme heat activities. Moreover, the study also found that the effect of using mung bean skin extract after high temperature treatment is better than that before high temperature treatment. This implies that drinking mung bean soup in hot summer is a very good summer resort. At the same time, in vitro studies also found that the active substances in mung beans can inhibit the growth of a variety of cancer cells.
Finally, I want to give you a healthy summer drink:
Honey, soybean and green soybean milk
Materials: 1 soymilk machine, 50g soybeans (soaked for 8h), 50g mung beans, 1000ml purified water.
Production: Put the beans and water into the soymilk machine, beat them into paste, add 2 spoonfuls of honey, stir them evenly, and serve.
Efficacy: It can supplement water, protein, starch, B vitamins, potassium, magnesium, dietary fiber, antioxidants and other functions.
Suitable: poor appetite in hot weather, drink when the diet is insufficient. But, like mung bean soup, don't overdo it. So is this mung bean soybean milk. Just two drinks.