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Sour radish, sour cowpea, sour cucumber... Just listening to this series of dish names, your teeth are already softening and your mouth is watering.

"Kimchi", as a product of the art of time and temperature, can be said to be flourishing everywhere in my country. Hunan's sour radish and old duck soup, Sichuan and Chongqing's sour beans and minced meat, and of course, the most spectacular, the pickled cabbage in Northeast China - in late autumn, carts of cabbage are transported to the downstairs of the community, and the autumn wind blows them until the skin is dry, and then the pickled cabbage jar and the pressure stone are taken out from the home, and after a period of time, it becomes the pickled cabbage and pork, pickled cabbage vermicelli, pickled cabbage hot pot on the winter table...

Pickled cabbage and pork hot pot. Copyright image. Reproduction may cause copyright disputes.

However, the various opinions about kimchi in recent years have made people feel confused. Some people say that kimchi contains nitrites, which may cause cancer, while others say that kimchi contains lactic acid bacteria, which are probiotics, so kimchi is a healthy food. Which one is correct? Let's make it clear today~

How is kimchi made?

Although the production of kimchi in different places may be somewhat different, in general, the vegetables are placed in a large jar, poured with salt water to cover the vegetables, and then the jar is sealed, and lactic acid bacteria are used to ferment and decompose the sugars in the food and release acid.

A jar of excellent kimchi needs to meet three requirements:

—— “Fresh”, “sour” and “crisp” .

Looking at the flavors that humans are obsessed with, umami ranks first. The umami flavor in food often comes from some umami amino acids, such as glutamic acid, aspartic acid, lysine, tyrosine, etc. Whether it is the deliciousness of fish and mutton, or the umami flavor of mushrooms, they are inseparable from the flavor amino acids. The monosodium glutamate, chicken essence, and various umami seasonings we use for cooking are inseparable from the blessing of the above-mentioned flavor amino acids. For example, the main ingredient of monosodium glutamate is sodium glutamate.

The fermentation process of kimchi, which is dominated by lactic acid bacteria, produces a large amount of umami amino acids . Studies have found that fermented vegetables, whether Sichuan kimchi, Jiangxi salted vegetables or Northeast pickled vegetables, are rich in amino acids such as glutamic acid, phenylalanine, alanine and aspartic acid. Although the types of amino acids in different types of fermented vegetables are different and the content will also change with the fermentation time, in short, the presence of these umami substances is the basis of the delicious taste of kimchi.

Lactic acid bacteria fermentation also produces organic acids. This sour taste is not as "pungent" as the sour taste brought by vinegar, but is more mild and has a special sour aroma. This is the result of the continuous change of organic acids during the fermentation process to produce alcohols and esters.

"Crisp" is not a taste, but a texture. People's love for "crisp" can be said to be instinctive: on the one hand, it comes from the desire for freshness - crisp fruits and vegetables usually represent sufficient moisture, freshness and fullness; on the other hand, it comes from the yearning for the crispy taste after cooking. Crisp foods are often baked or fried, which causes the Maillard reaction that can bring fragrance, attractive color and taste.

Compared with other pickled vegetables, kimchi's unique crispness has won more people's love. The "crispness" of kimchi is not only affected by the freshness of the pickled vegetables, but also by the length of pickling time, pickling temperature, and pH value in the kimchi jar. So, although kimchi seems simple, the success rate for novices is not high. It is precisely by accumulating experience in the above details that experts can pickle delicious kimchi that is crisp, sour and fragrant.

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Is kimchi carcinogenic, high in salt, and unhealthy?

In recent years, due to changes in life concepts, many people’s impression of kimchi has changed from “delicious, cheap, and convenient” to “carcinogenic, high in salt, and unhealthy”. Is it really true that kimchi cannot be eaten anymore?

First of all, we have to admit that kimchi is far inferior to fresh vegetables in terms of nutritional value and health. On the one hand, the pickling process causes a large loss of vitamins in fresh vegetables; on the other hand, no matter which method is used to make kimchi, a large amount of salt is inevitably used . Eating kimchi for a long time will indeed increase the risk of high blood pressure. In addition, a long-term high-salt diet is also a risk factor for gastric cancer.

However, the harm caused by high salt in kimchi depends on how much and how often we eat it. As long as we can control the frequency and amount of eating, we can also reduce the adverse effects of high salt.

Secondly, another health risk of kimchi is nitrite. During the pickling process of vegetables, the nitrate in them will be converted into nitrite by bacteria, and nitrite can be further converted into nitrosamine in the stomach. Nitrosamine is a carcinogen that can easily cause digestive tract cancer.

Although nitrosamines are carcinogenic, it does not mean that kimchi is "poisonous". The production of nitrites will change with the length of pickling time.
According to experimental calculations, the nitrite content in pickled vegetables first gradually increases, reaching a peak around one to two weeks after pickling, and then gradually decreases to within the national limit after 20 days, and usually reaches 3 mg/1000 g after 30 days, which is in line with the provisions of our country's "National Food Safety Standard Limits of Contaminants in Food (GB2762-2017)" on the nitrite content in pickled vegetables - no more than 20 mg/1000 g. This means that we can reasonably avoid the harm of nitrite according to the pickling time.

Image source: Reference [3]

Kimchi contains lactic acid bacteria

Are “fermented products” healthy?

Regarding kimchi, there is now a saying that it is a "intestinal health product" that can improve intestinal flora. Is this statement reasonable?

Experiments have confirmed that fermented foods such as kimchi can supplement intestinal probiotics and play a role in reducing the body's inflammatory response. However, considering that these probiotics are mainly found in kimchi soup and kimchi itself is high in salt, it is still not recommended that you rely on eating more kimchi to obtain intestinal probiotics.

We can get probiotics through healthier fermented foods such as yogurt and cheese. People with normal intestinal flora do not need to supplement too much probiotics. Just pay attention to a balanced diet and eat more fresh vegetables and coarse grains rich in dietary fiber, which can also promote the healthy growth of intestinal flora.

Eat kimchi like this

Lower health risks

Therefore, if you want to eat kimchi safely, you just need to find a balance between deliciousness and health. You can refer to the following methods to reduce the health risks of eating kimchi:

1. To make homemade kimchi, you can directly buy pure lactic acid bacteria powder for fermentation. By avoiding the presence of miscellaneous bacteria, the possibility of producing nitrite is reduced.

2. Extend the fermentation time: Try to eat it after 20 days to 1 month of pickling.

3. Seal well: Whether during the pickling period or after eating, you should pay attention to sealing to prevent bacteria from entering and increasing the nitrite content.

4. Low-temperature refrigeration: After eating, you can use low-temperature refrigeration to slow down the production of nitrite.

5. Do not buy bulk kimchi from street vendors. These informal products may have problems such as insufficient pickling time and impure fermentation bacteria, which may lead to high nitrite content and increase health risks.

6. Eat in small amounts and rinse with water before eating.

7. Use kimchi instead of salt to stew or stir-fry. This method can not only add more fresh vegetables and supplement the vitamins lacking in kimchi, but also play a role in "reducing salt", killing two birds with one stone!

Overnight pickled kimchi vs bath kimchi vs traditional kimchi

Which one is more recommended

In recent years, there are more and more varieties of kimchi. From the "one-night pickle" kimchi full of Japanese freshness to the bathing kimchi (also called diving kimchi) in Sichuan and Chongqing, which of these kimchi is more recommended compared to traditional kimchi?
The so-called overnight pickles, like bathing kimchi/diving kimchi, are kimchi that can be eaten after just a few hours or overnight pickling. This is a huge difference from the traditional kimchi pickling time of a month or even longer, and it is more convenient.
In terms of flavor, the traditional kimchi that is pickled for a longer time is definitely more flavorful, after all, the fermentation process can produce more flavor substances such as acids, esters, and alcohols. Of course, some people think that although the bath kimchi is not sour and fragrant, it is refreshing and tender. This is a subjective judgment, and we will not discuss it for now.

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From the perspective of food safety, the nitrite content of traditional kimchi that has been pickled for more than one month is already very low, usually below the safety limit specified by national standards, and moderate intake will not threaten health. However, since overnight pickles, bathing kimchi/diving kimchi are pickled for a very short time, nitrite has not yet been produced in large quantities. In addition, this type of short-term pickles are often added with white wine and stored in low-temperature refrigeration, which is not conducive to the reproduction of miscellaneous bacteria and the production of nitrite. Therefore, it is safe as long as the pickling hygiene can be guaranteed. However, this type of kimchi is best eaten within 2 to 3 days, otherwise the nitrite content will gradually increase.

From the perspective of salt content, traditional kimchi has a high salt content, but overnight pickled kimchi, bathing kimchi/diving kimchi are not necessarily lower in salt. In order to make pickling easier and increase the flavor of this type of kimchi, a large amount of salt must first be used to "kill" the moisture in the vegetables, and salt and a large amount of sugar must be added during pickling (in some recipes, 100 grams of sugar is used to pickle two white radishes and one cucumber). If you eat too much at one time, it will also increase the intake of salt and sugar, which will have an adverse effect on the stability of blood pressure and blood sugar.

It can be seen that as long as the pickling time and hygiene of the pickling process are taken care of, there should be no major safety issues for these two types of kimchi, and they are delicious in their own way. The only thing to note is that it is wise to control the intake and only try them as a side dish occasionally.

References

[1] Zhang Yulin, Chen Hongfan, Zhao Zhiping. Analysis of differential metabolites and related metabolic pathways of long-term fermented kohlrabi[J]. Food Science, 2022, 43(22): 192-198.

[2] Ma Huanhuan, Lü Xinran, Lin Yang, Sun Mengtong, Bai Fengling, Li Jianrong. Synchronous analysis of lactic acid bacteria and nutrients during natural fermentation of traditional Northeastern pickled cabbage[J]. Food and Fermentation Industries, 2017, 43(02):79-84.

[3] Zhang Zhiguo, Wang Guangyin, Sun Jianquan. Dynamic study on nitrite content in kimchi [J]. Chinese Condiments, 2008(4):40-42.

[4] National Health Commission of the People’s Republic of China, State Administration for Market Regulation. National Food Safety Standard Limits of Contaminants in Food (GB2762-2022).

[5]Wastyk HC, Fragiadakis GK et al. Gut-microbiota-targeted diets modulate human immune status[J]..Cell, 2021 Aug 5;184(16):4137-4153.

Planning and production

This article is a work of Science Popularization China-Starry Sky Project

Produced by: Science Popularization Department of China Association for Science and Technology

Producer｜China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Author: Wang Lu, registered dietitian

Review | Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center

Planning丨Yang Yaping

Editor: Yang Yaping