Recent worldwide popularity in kimchi has highlighted it as a dish with many health benefits. The Chinese cabbage fermented with lactic acid bacteria and seasoning is linked with a plethora of health benefits, including anti-cancer, immune system boosting, and antioxidant properties. Whilst we understand the basic health benefits, the biochemistry and metabolites underpinning this dish have eluded scientists. Dr Ho-Jin Kim and Ms Min-Hee Jeong have studied glucosinolates and their metabolites to better understand why kimchi is such a good dish for healthy eating.
South Korea is a nation whose culture is reaching a global audience. From the rise of eSport teams, to the international success of K-pop artists and also Korean cuisine. One dish, however, that is gaining popularity is kimchi.
Kimchi is a traditional Korean pickled side dish, consisting of vegetables (usually Chinese cabbage or Korean radishes) and salted seafood fermented with a multitude of seasoning, including chilli powder, ginger, garlic, and spring onions. Kimchi is then fermented with lactic acid bacteria at a low temperature.
Kimchi effectively began as a form of food storage; vegetables were fermented in ceramic pots buried inside the ground to prevent it from freezing in the winter, and to decelerate its fermentation process during the summer. Kimchi became second-nature to Koreans who needed to preserve vegetables during the sparse winter months.
Keeping kimchi in Korea
Kimchi is one of the unique staples of the Korean diet. Traditionally, however, it has remained largely homebound, with Koreans assuming its strong aroma of flavours and its saltiness wouldn’t prove popular abroad. However, in 2020 South Korea recorded a record high in kimchi exports, reaching a mindboggling $144.51 million. But how did kimchi become popular throughout the world?
As kimchi has toured the world to become an international star, it has developed a reputation largely as a low-calorie and nutritious dish. The bacteria involved in its fermentation process act as a natural probiotic, roughly analogous to yogurts in western diets, which aid digestion and reduce cholesterol. Kimchi also has a reputation as an anti-oxidant and anti-carcinogen, and contains lots of vitamin C, boosting the immune system.
Although we are well aware of kimchi’s broad health benefits, zooming into the molecular basis for these benefits produces a patchier picture. We understand how some of the vitamins and minerals, such as vitamin C, vitamin K, and choline, are beneficial. But some compounds, like the glucosinolates, have remained elusive.
Glucosinolates (GLS) are a group of secondary metabolites – chemicals or compounds produced by an organism that aren’t designed to influence its normal growth or reproduction. They give the organism an evolutionary advantage by their impact on the competition, for example by inhibiting the growth of pathogenic bacteria or competitive plants. GLS are secondary metabolites in the Brassicaceae family of plants, ie, the mustard group, which includes cabbages, radishes, and the other cruciferous vegetables. GLS evolved as an innate defence molecule that can protect the plants from pathogenic microorganisms. GLS are of interest to for their role in kimchi. Not only do they give a cruciferous vegetable its characteristically bitter taste, but they also break down during its decomposition and fermentation.
Multiple rounds of enzyme action can produce a variety of different molecules, depending on the specific type of GLS and its structure, as well as the particular conditions of decomposition. It’s these products that are strongly linked to the many health benefits of kimchi, including its anti-cancer, antioxidative, and immune support properties.
And it was these products which caught the interest of Dr Ho-Jin Kim and Ms Min Hee Jeong, two researchers at the National Agricultural Products Quality Management Service, an agricultural regulator of the South Korean government.
Glucosinolates in kimchi
Dr Kim and Ms Jeong’s work has explored the biochemical profile of GLS for the first time to provide the foundation for understanding their health benefits. One study led by Dr Kim looked at the GLS profile of 20 different Chinese cabbage-based kimchis sold in supermarkets. They conducted liquid chromatography mass spectrometry (LC-MS) on each kimchi sample to split and identify the
composition of organic molecules.
Each sample was extracted for its GLS profile, and pumped into a liquid chromatography column at high pressure to separate different molecules in the samples. The now separated column was then directed to a mass spectrometer, to ionise and separate the samples for detection.
Conducting this analysis on 20 supermarket kimchis, Dr Kim and his colleagues found five different and distinct compounds: glucoalyssin, gluconapin, glucobrassicanapin, glucobrassicin, and 4-methoxyglucobrassicin.
Different kimchi brands had varying concentrations of each type of compound, giving each one a unique chemical profile, and possibly giving each brand and recipe of kimchi its own unique health benefits.
However, the GLS molecules themselves aren’t necessarily the most important aspect of this research. As the fermentation process decomposes GLS into substrate molecules, the type of substrate molecules depends on both the GLS used as well as the fermentation process.
Upon fermentation, it’s known that GLS can break down into various different molecules and compounds. These include isothiocyanates
(ITCs), a group of chemicals which prevent cancer by inhibiting cell growth and promoting the controlled death of potentially cancerous cells. ITCs have been linked to the prevention of liver, lung, and stomach cancers. Other experiments have also hinted at their
ability to suppress breast and skin cancer tumours. One type of ITC, known as sulforaphane, also aids the metabolism of glucose in the stomach.
The researchers sought to expand our knowledge of the biochemical profile of kimchi by looking at other GLS metabolites, such as volatile organic compounds (VOCs). VOCs are already important in giving kimchi its unique sour taste, and the research team wanted to explore VOCs more closely, which had been overlooked previously.
Twenty-two different samples of kimchi were subject to gas chromatography, vaporising the liquid kimchi samples to separate the compounds. With this separation, they were able to detect the different types of GSL compounds present as well as their VOC composition.
The researchers found 12 different GLS chemicals split into five different types, including seven different types of isothiocyanates. Dr Lee and Ms Jeong found an even greater diversity of VOCs, detecting 52 different VOCs including (but not limited to) acids, alkanes, alcohols, ketones, and multiple different types of hydrocarbons.
Strength in diversity
As well as confirming the molecular health benefits that kimchi provides, Dr Kim and Ms Jeong hope that this research can be the platform for future research to better understand the biochemistry and molecular biology behind its health benefits. By looking at the different GLS compounds and VOCs, researchers can understand how it provides anti-carcinogenic properties, or compare different types of kimchi for their properties and health benefits.
Whilst many South Koreans may not have expected this interest in their traditional dish, it’s perhaps not that surprising. The findings from these studies provide evidence of the excellent health benefits from kimchi.
In the year that South Korea celebrated a record-high profit from kimchi exports, they also celebrated Parasite becoming the first foreign-language film to win the Oscar for Best Picture. It’s a reminder of the strength of culture diversity, even in health and medicine.
- Kim, H-J Lee, MJ Jeong, MH and Kim, JE (2017). Identification and Quantification of Glucosinolates in Kimchi by Liquid Chromatography-Electrospray Tandem Mass Spectrometry. International Journal of Analytical Chemistry, 2017, ID 6753481.
- WebMD (2021). Health Benefits of Kimchi. [online] WebMD.com. Available at: https://www.webmd.com/diet/health-benefits-kimchi#1 [16/09/2021].
- Cheung, J (2020). Kimchi: How South Korea’s National Dish Went Global. [online] Culture Trip. Available at: https://theculturetrip.com/asia/south-korea/articles/how-kimchi-went-global/ [16/09/2021].
Dr Ho-Jin Kim and Ms Min-Hee Jeong investigate the health benefits of Korean kimchi.
Dr Kim and Ms Jeong
National Agricultural Products
Quality Management Service
Republic of Korea