Pickled radish, sour cowpea, pickled cucumber... just listening to this series of dish names will make your teeth feel soft and your mouth will salivate. "Kimchi", as a product of an art intertwined with time and temperature, can be said to be blooming everywhere in our country. Hunan's pickled radish and old duck soup, Sichuan and Chongqing's pickled beans and minced meat, and of course, the most spectacular, the Northeast's pickled cabbage - in late autumn, truckloads of cabbage are transported downstairs to the community. When the autumn wind blows them until their skins are dry, they take out the pickled cabbage vat and pressing stone at home. After waiting for a while, they become pickled cabbage white meat, pickled cabbage vermicelli, pickled cabbage hot pot... on the winter table...

However, various opinions about kimchi over the years have left people confused as to what to do - some say that kimchi contains nitrite, which may cause cancer, while others say that kimchi contains lactobacilli, which are probiotics, so kimchi is a healthy food. Which statement is correct? Let’s make it clear today~

How is kimchi made?

Although there may be some differences in the preparation of kimchi in different places, in general, the vegetables are put in a large jar, poured with salt water to cover the vegetables, then the jar is sealed, and lactic acid bacteria are used to ferment the sugars in the food and release acid.

An excellent jar of kimchi needs to satisfy three words——“Fresh”, “sour” and “crisp”.

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

The kimchi fermentation process is dominated by lactic acid bacteria.Produces a large amount of umami-flavoring amino acids. Research has found that fermented vegetables, whether they are Sichuan kimchi, Jiangxi salted vegetables, or Northeastern sauerkraut, 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 change with the fermentation time, in short, the existence 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 "exciting" as the sour taste brought by vinegar, but is more mild and has a special sour aroma. This is the result of organic acids constantly changing 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 originate from instinct: on the one hand, it comes from the desire for freshness - crisp fruits and vegetables usually represent sufficient moisture, freshness and plumpness; on the other hand, it comes from the yearning for the crispy texture after cooking. Crispy foods are often baked or fried, resulting in the Maillard reaction that brings aroma, attractive color and taste.

Compared with other pickled vegetables, kimchi is uniquely crispy and has won the favor of more people. The "crispness" of kimchi is not only affected by the freshness of the pickled vegetables, but also related to the length of pickling time, pickling temperature, and the pH value in the kimchi jar. Therefore, kimchi seems simple, but the success rate for beginners is not high. Experts have accumulated experience in the above details to make delicious pickles that are crisp, sour and fragrant.

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 impossible to eat kimchi?

First of all, you have to admit,In terms of nutritional value and health, kimchi is indeed far inferior to fresh vegetables.On the one hand, the pickling process greatly reduces the vitamins in fresh vegetables; on the other hand, no matter which method you use to make kimchi, you will inevitably use a lot of salt.Eating large amounts of kimchi over a long period of time does increase the risk of high blood pressure. In addition, long-term high-salt diet is also a risk factor for gastric cancer.

However, the harm caused by the high salt content of kimchi also depends on how much we eat and how often we eat it.As long as the frequency and quantity of food can be controlled, the adverse effects of high salt can be reduced.

Secondly,Another health concern with pickles is nitrites.During the pickling process of vegetables, the nitrate in them will be converted by bacteria into nitrite. The nitrite can be further converted into nitrosamines in the stomach. Nitrosamines are carcinogens that can easily cause digestive tract cancer.

Although nitrosamines cause cancer, it does not mean that kimchi is "poison".The production of nitrite will change with the length of marinating time.

According to experimental calculations, the nitrite content in pickled vegetables first gradually increases, reaching a peak about one to two weeks after pickling, and will gradually decrease to within the national limit standard after 20 days.It can usually reach 3 mg/1000g after 30 days.It complies with our country's "National Food Safety Standard Limits of Contaminants in Food (GB2762-2017)" regulations on nitrite content in pickled vegetables - no more than 20 mg/1000g. This means that we can reasonably avoid the harm of nitrite based on the marinating time.


Image source: Reference [3]

Kimchi contains lactic acid bacteria and is it a healthy "fermented product"?

Regarding kimchi, there is still a saying that it is called an "intestinal health product" and 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. But consideringThese 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 like yogurt and cheese. Friends with normal intestinal flora do not need to supplement too many probiotics. Just pay attention to a balanced diet and eat more fresh vegetables and whole grains rich in dietary fiber, which can also promote the healthy growth of intestinal flora.

Eat kimchi like this

Lower health risks

It can be seen that if you want to eat kimchi with peace of mind, it is nothing more than finding 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 purchase pure lactic acid bacteria powder for fermentation. Reduce the possibility of nitrite production by avoiding the presence of miscellaneous bacteria.

2. Extend the fermentation time: Try to marinate for 20 days to 1 month before eating.

3. Seal well: Whether during pickling or after eating, you should pay attention to sealing to avoid the entry of foreign bacteria and increase 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 kimchi in bulk from vendors. These informal products may have problems such as insufficient curing time and impure fermentation strains, resulting in higher nitrite content and increased health risks.

6. Eat a small amount and rinse with water before eating.

7.Use kimchi instead of salt in stews or stir-fries.This method can not only be paired with more fresh vegetables and supplement the vitamins lacking in kimchi, but also have the effect of "reducing salt", killing two birds with one stone!

Overnight pickles VS bath kimchi VS traditional kimchi

Which one is more recommended?

Over the years, there have been more and more varieties of kimchi. From the Japanese-style "One Night Pickle" kimchi, which is full of fresh Japanese style, to the bathing kimchi (also called diving kimchi) from Sichuan and Chongqing, which one of these kimchi is more recommended compared with traditional kimchi?

The so-called overnight pickles, like bath kimchi/dive kimchi, are kimchi that only need to be pickled for a few hours or overnight. This is a huge difference from the traditional pickling time of one month or even longer, which makes it more convenient.

In terms of flavor, traditional kimchi that has been pickled for a longer time is definitely more flavorful. After all, the fermentation process can produce more acids, esters, alcohols and other flavor substances. Of course, some people think that although bath kimchi is not sour and fragrant, it is refreshing and crispy. This belongs to the subjective judgment of each flower, so we won’t mention it for now.

From a food safety perspective,The nitrite content of traditional kimchi that has been pickled for more than one month is already very low, usually lower than the safety limit specified by national standards. Moderate intake will not threaten health.However, the pickling time of overnight pickles, bath pickles/diving pickles is very short, and nitrite has not yet had time to be produced in large quantities.In addition, this kind of short-term kimchi is often added with white wine and stored at low temperature, which is not conducive to the reproduction of miscellaneous bacteria and the production of nitrite. Therefore, it is safe as long as the hygiene of pickling can be ensured. However, it is best to eat this kind of kimchi 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 it is not necessarily lower if it is soaked overnight or bathed or dipped in water. In order to facilitate pickling and increase the flavor of this kind of kimchi, a large amount of salt must first be used to "kill" the water in the vegetables. Salt and a large amount of sugar are also added during pickling (in some recipes, 100 grams of sugar is used to pickle two white radish and one cucumber). If you eat too much at one time, you will also increase your salt and sugar intake, which will have a negative impact on the stability of blood pressure and blood sugar.

It can be seen from this thatAs long as you pay attention to the pickling time and hygiene during the pickling process, there should be no major safety issues with these two types of kimchi, and their tastes also have their own characteristics. The only thing that needs to be noted is that it is wise to control the intake and only try it as a side dish occasionally.

References

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

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

[3] Zhang Zhiguo, Wang Guangyin, Sun Jianqian. 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]WastykHC, FragiadakisGKetal.Gut-microbiota-targeteddietsmodulatehumanimmunestatus[J]..Cell, 2021Aug5;184(16):4137-4153.

Planning and production

This article is a work of Popular Science 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 Galaxy Culture Media Co., Ltd.

Author丨Wang Lu registered nutritionist

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

Planning丨Yang Yaping

Editor丨Yang Yaping

Reviewer丨Xu Lai Linlin