A recent Fermentation journal study reviews various traditional Korean fermented foods for their biological functions, production, and future contribution to global wellness.
Study: Fermented foods of Korea and their functionalities. Image Credit: PAPA WOR / Shutterstock.com
Common Korean fermented foods
Food is fermented by microbial biochemical reactions, during which organic substances are synthesized or decomposed to produce new products, including fatty acids, organic acids, and vitamins. These microorganisms may also act as probiotics, thus further enhancing the health benefits of fermented food.
The most common Korean fermented food products include kimchi, jang, jeotgal, and vinegar. Kimchi, for example, which is considered Korea's signatory fermented food, was historically prepared using various vegetables, including cabbage, sweet potatoes, eggplant, dropwort, radish, leaf mustard, turnip, and lettuce.
Although soybean is the primary ingredient for jang, it is often accompanied by grains, red peppers, and salt. Comparatively, jeotgal, which is also used to enhance the flavor of food products like jang, is a fermented fish product; shrimps, mollusks, squids, octopuses, and crustaceans can also be used to prepare this product.
Vinegar, the oldest fermented food product used in Korea, is typically prepared through alcohol fermentation, followed by acetic fermentation, achieved through the inoculation of acetic acid bacteria. Like other countries worldwide, Korean cuisine incorporates vinegar into various food products to induce a refreshing and sour taste.
Most fermented food products commonly incorporated into Korean meals have historically been used for their health benefits. Despite the high salt content of these food products, particularly jang, limited evidence has correlated the consumption of jang with hypertension.
Instead, several studies have shown that some Korean fermented food products may be associated with anti-hypertensive health benefits. Doenjang, for example, is produced through a long fermentation product that has contributed to its ability to reduce blood pressure (BP) levels and control the renin-angiotensin system (RAS).
Cheonggukjang also aids in regulating BP. Comparatively, gochujang consumption suppresses thrombolysis and inhibits angiotensin-converting enzyme (ACE) activity and platelet aggregation.
Evidence from one previous survey suggested that people who regularly consumed kimchi also had relatively lower blood pressure; however, more studies are needed.
Several studies have investigated the impact of kimchi on body weight, with various factors, including the degree of fermentation and ingredients, contributing to this beneficial effect. Kimchi with red pepper, for example, appears to reduce perinephric fat pads and body weight and promote fat loss and energy consumption.
Previous studies have also reported the reduced expression of obesity-related genes in obese individuals consuming kimchi. In addition, kimchi consumption in these individuals also reduced markers for metabolic diseases such as insulin, high-density lipoprotein cholesterol (HDL-C), BP, and C-reactive protein (CRP).
Depending on the duration of fermentation of doenjang, its protective effects against metabolic diseases-associated risk factors differ. Nevertheless, doenjang has been shown to be highly effective against obesity, as demonstrated by computed tomography (CT) images and the reduced expression of genes associated with the development of fat cells.
Several studies have also confirmed the anti-obesity effects of fermented and non-fermented gochujang. Furthermore, gochujang also improves lipid profiles and reduces visceral fat levels, whereas cheonggukjang enhances lipid metabolism and exhibits anti-obesity effects.
Persimmon vinegar has been shown to be effective in regulating blood glucose levels and body weight, along with improving lipid metabolism. These effects are likely due to the high level of organic acids present in this product, some of which include acetic, citric, and malic acids.
The metabolites and active compounds present in kimchi likely support the effective management of diabetes. In fact, in vivo results have demonstrated that four weeks of kimchi consumption successfully reduced blood glucose levels in an animal model of type 2 diabetes.
When obese people consume gochujang, their insulin sensitivity generally improves, which regulates their glucose levels. In addition, cheonggukjang has high fiber content with a low glycemic index, thus making it appropriate for managing blood glucose levels.
Cheonggukjang also comprises a trypsin inhibitor that increases insulin sensitivity and secretion. In clinical settings, the consumption of cheonggukjang for eight weeks has been shown to reduce fasting blood glucose, low-density lipoprotein cholesterol (LDL-C), and total cholesterol levels. This product also suppresses a-glucosidase activity, thereby improving insulin resistance.
Cucumber vinegar has also been shown to regulate insulin levels.
Kimchi inhibits lipid production in blood vessels. Moreover, the consumption of aged kimchi significantly decreases pro-inflammatory cytokine levels often associated with arteriosclerosis.
In obese individuals, aged kimchi has been shown to reduce BP levels, fasting blood glucose, and body fat percentage, all of which are risk factors for metabolic syndrome. In healthy individuals, the consumption of cabbage kimchi has been associated with reduced blood LDL-C/HDL-C ratio, triglycerides (TG), and arteriosclerosis index. Furthermore, pre-diabetic patients' consumption of fresh and fermented kimchi can improve lipid metabolism, obesity, and inflammation.
Doenjang reduces the risk of cardiovascular disease and arteriosclerosis by reducing LDL-C, total cholesterol, and very-low-density lipoproteins (VLDL)-C levels and inhibiting thrombin production, lipid synthesis, and delaying fibrin coagulation. In addition, this food product also suppresses thrombolysis and platelet aggregation.
Fermented gochujang positively impacts lipid metabolism and has also been shown to reduce hyperlipidemia, LDL-C, total cholesterol levels, and obesity.
Protease, which is present in cheonggukjang, suppresses cholesterol synthesis and has antithrombotic effects. Cheonggukang is also rich in indigestible saccharides and dietary fiber that reduce the absorption of total cholesterol and triglycerides and promote fecal lipid excretion, thus aiding in the prevention of arteriosclerosis.
Clinically, the consumption of cheonggukjang had anti-arteriosclerosis effects in overweight individuals. Cheonggukjang also appears to reduce arteriosclerosis-associated index protein.
Microorganisms in kimchi act as probiotics that positively affect intestinal health. Lactic acid bacteria in kimchi decrease intestinal pH and inhibit intestinal toxin absorption and the proliferation of harmful bacteria. Notably, kimchi consumption is often associated with beneficial effects in irritable bowel syndrome (IBS) patients.
Doenjang fermentation produces vitamin B12 and K2. The Bacillus sp present in cheonggukjang improves overall intestinal health, eases intestinal movement, and suppresses harmful bacteria. Regular cheonggukjang consumption relieves symptoms of inflammatory colitis.
Kimchi has anti-cancer and anti-mutagenic effects against known carcinogens, with fermented kimchi associated with a greater degree of anti-mutagenic effects. Cancer preventive kimchi (CPK) reduces the risk of inflammation and gastric cancer and alleviates certain cancer symptoms.
Ganjang is also associated with certain anti-cancer properties. When sesame seeds are added to ganjang, their anti-cancer properties are enhanced. In addition, ganjang older than 15 years can significantly increase natural killer (NK)-cell activity and the proliferation of spleen cells.
Meju, the raw material used in the preparation of doenjang, is susceptible to fungi producing aflatoxin. Prolonged aflatoxin exposure increases the risk of developing cancer.
Doenjang older than one-year harbors microorganisms that restrict the production of aflatoxin. An extended fermentation period increases the anti-metastasis and anti-cancer effects of doenjang. Furthermore, doenjang has tumor-suppressive and liver-detoxification effects.
Gochujang also has anti-cancer and anti-metastasis properties. The anti-cancer benefits of this food product increase with more extended fermentation periods, thereby making these effects of traditional gochujang more pronounced.
Bay salt utilized in the preparation of jeotgal has been attributed to its anti-mutagenic activity. Unfermented jeotgal also exhibits anti-mutagenic activity.
The antioxidant action of cheonggukjang is proportional to the presence of isoflavone and polyphenol contents.
The immune system
The consumption of kimchi in adequate amounts can reduce the severity of allergic rhinitis, atopic dermatitis, and asthma. Similarly, doenjang enhances immunity and is associated with antioxidant, anti-inflammatory, and immunomodulatory activities.
Cheonggukjang has immunomodulatory properties, enhances immunological functions, and alleviates allergies. Likewise, jeotgal has anti-inflammatory properties and a broader anti-allergic effect.
Oxidative stress and aging
Aged kimchi consists of several antioxidant substances, including vitamins C and A, lactic acid bacteria, and various metabolites, all of which support the removal of free radicals. When mustard leaf is used to prepare kimchi, anti-aging effects are provided through its ability to reduce the production of free radical species in the brain.
Cheonggukjang also consists of several compounds capable of reducing oxidative stress and inflammation, including isoflavone, glycans, peptides, dietary fiber, and microorganisms.