Is the "green" bean soup you drink red or green?

In the hot summer, many families will cook a bowl of mung bean soup and keep it in the refrigerator. When they are thirsty, they will drink a bowl of it, which is refreshing and cool. However, is this ordinary bowl of mung bean soup green or red? In addition to the color, there are many sayings about mung bean soup, such as drinking it often can "detoxify" and people with poor stomachs should drink less... Are these true?

Let’s talk about these little issues about mung bean soup today.

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green beans

High-protein, low-fat, high-quality beans

To understand mung bean soup, you must first understand its protagonist - mung bean. According to the recommendation of the "Dietary Guidelines for Chinese Residents", it is recommended that each person eat 50-150g of whole grains and miscellaneous beans every day, and mung bean is a kind of miscellaneous beans.

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From the nutritional point of view of mung beans themselves, it has the shining quality of high protein and low fat, and is rich in dietary fiber, which can enhance satiety and prevent constipation. It should be noted that although mung beans are rich in protein, they are rich in lysine and lack methionine, while most cereal foods are rich in methionine and lack lysine, so it is a good idea to eat mung beans and cereal foods together, so as to give full play to the complementary effect of protein. For example: mung beans and rice are made into mixed bean rice or mixed bean porridge. The recommended ratio is mung beans: rice = 1:3~1:2. At the same time, this way of eating is also in line with the principle of coarse and fine matching of staple foods, and is especially recommended for those who need to lose weight and control blood sugar.

In addition, the calcium content in mung beans is also excellent among miscellaneous beans, 1.1 times and 1.2 times that of red beans and white lentils respectively; the iron content of mung beans is nearly twice that of chickpeas. Vegetarian friends can eat mung beans often to supplement iron. [1]

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The popularity of mung bean is also due to its rich content of polyphenols, which gives it strong antioxidant activity, can inhibit amylase activity, and help to slow down the rise of blood sugar after meals and prevent diabetes. In particular, the flavonoids present in mung bean skin are good for cardiovascular health and have certain anti-cancer activity.

Mung Bean Soup

"Relieve heat" is reliable, "detoxify"... forget it

Mung beans are often called "a great way to cool down in summer". In the hot and humid days of the dog days, drinking a bowl of refreshing mung bean soup can not only "take away" the heat, but also replenish water and nutrients. It is simply wonderful. The potassium and B vitamins in mung beans are good nutrients, which can just make up for the loss of nutrients caused by sweating in high temperatures.

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Therefore, it is reasonable to say that mung bean soup can relieve heat. However, the claim that it can detoxify is a bit exaggerated.

The definition of "poison" is very vague. In fact, a healthy person's body does not have that much "poison" to eliminate. The waste produced by normal metabolism and some harmful substances ingested can be discharged normally through the human body's metabolic system. In current academic research, mung beans do not have any "poison"-eliminating effect.

Red or green?

What color is mung bean soup

Raw mung beans are bright green in appearance, otherwise they wouldn't be called mung beans. But why is the finished mung bean soup often red? Is there something wrong with the mung beans?

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In fact, this change from green to red is a normal change. The red color of mung bean soup is caused by the oxidation of polyphenols. As we said before, mung bean skin contains a large amount of polyphenols. In the process of cooking mung bean soup, the polyphenols dissolved in the mung bean skin react with the oxygen in the air, which will cause the mung bean soup to turn red.

In addition, it is not just the cooking time that affects the color of the mung bean soup. The acidity or alkalinity of the water used to cook the mung beans also affects the color of the mung bean soup. An experiment studied the relationship between the acidity or alkalinity of the cooking water and the color of the mung bean soup. The results showed that weakly alkaline water would gradually change the color of the mung bean soup from green to red. This change would also lead to a decrease in the antioxidant capacity of the mung bean soup. [3]

Therefore, if you use weakly acidic water or purified water to cook mung bean soup, you can see the original green color, and if the water is alkaline, you will see a reddish mung bean soup.

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Tips for "locking the color" of mung bean soup

If you want to keep the green color of the mung bean soup, in addition to working on the water, there are some other methods you can try:

① After washing the mung beans, soak them for 2 hours. Do not discard the soaking water, because after soaking for a long time, the polyphenols in the mung bean skin will dissolve in the soaking water. [4]

②Add a few drops of lemon juice when cooking mung bean soup.

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③ When cooking mung bean soup, do not add alkali to make it softer. Adding alkali will not only turn the mung bean soup red, but also cause the loss of B vitamins and reduce antioxidant activity [5].

Effect of baking soda on the antioxidant activity of mung bean broth

④ Do not add sugar. Experiments have shown that adding sugar can also reduce the antioxidant capacity of mung bean soup, but adding salt can increase its antioxidant capacity [5]. Of course, if you add salt to mung bean soup, you should pay attention to reducing the amount of salt in your diet and control the total daily salt intake to no more than 6g (about 1 beer cap).

Effect of white sugar on antioxidant activity of mung bean broth

Effect of salt on the antioxidant activity of mung bean broth

⑤ Cover the lid when cooking mung bean soup, so that the mung beans can avoid contact with oxygen as much as possible and reduce oxidation and reddening. After cooking, don't open the lid in a hurry, cover it and let it cool before drinking.

Another point that everyone should pay attention to is that the cooking time should not be too long. It is recommended to control it within 1.2 hours. Cooking for too long will lead to a decrease in the content of flavonoids[6].

Effect of cooking time on flavonoid content

Summarize:

51. Mung bean soup is the standard "natural cooling drink" in summer. Healthy people can enjoy the refreshing feeling it brings. It is recommended to drink the soup and eat the beans.
52. Since mung beans are rich in dietary fiber, they can promote gastrointestinal motility and cause flatulence or abdominal pain. Therefore, for people with poor gastrointestinal function, it is recommended to drink more mung bean soup and eat less mung beans.
53. Also, making mung bean ice pops with the cooked mung bean soup is also a great way to cool down!

[1] Yang Yuexin. Chinese Food Composition Table 6th Edition Volume 1[M]. Peking University Medical Press, 2018

[2] Yang Lihong. Study on the detoxification effect of mung bean on arsenic poisoning[J]. Asia-Pacific Traditional Medicine, 2010, 6(08): 8-9.

[3] Chen Ran, Wang Jing, Wan Haijing, Zhao Jianjing, Fan Zhihong. Effects of pH value and metal ions in cooking water on mung bean broth[J]. Food Science, 2014, 35(03):96-99.

[4] Xu BJ , Chang SK . Total Phenolic Content and Antioxidant Properties of Eclipse Black Beans (Phaseolus vulgaris L.) as Affected by Processing Methods[J]. Journal of Food Science, 2010, 73(2):H19-H27.

[5] Chen Ran, Zhao Jianjing, Fan Zhihong. Effects of cooking conditions on the color and antioxidant activity of mung bean broth[J]. Food Science, 2012, 33(08): 115-120.

[6] Zhang Guifang, Yu Jinchi, Wang Ying, Zhang Dongjie. Effects of cooking on flavonoid content in mung beans[J]. Food Research and Development, 2017, 38(04): 38-41.

Author of this article: Xue Qingxin, member of Chinese Nutrition Society, registered dietitian, registered nutrition technician, health manager, public nutritionist

I review: Song Shuang, Associate Researcher, Institute of Nutrition and Health, Chinese Center for Disease Control and Prevention

Source: Science Refutes Rumors

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