Course:FNH200/Projects/2021/Kimchi
Introduction
Kimchi is a traditional Korean food made from fermented vegetables such as cabbage or radish with a variety of spices and seasonings. Kimchi can be made in a plethora of different ways, resulting in different properties and hundreds of classifications.[1] It first originated due to the demand for food storage during the long winters in Korea, and eventually developed into a Korean fall tradition. Nowadays, many Koreans still make homemade kimchi and the art of making it is considered a deep root in Korean culture, as well as a way to bond with others. Kimchi is considered a staple food in Korea, and has become immensely popular over the years with the introduction of Asian cuisine in the Western world. The growing interest in kimchi worldwide has increased its production, and many North American supermarkets now sell kimchi in their aisles. [2]
Pictures
Traditional kimchi fermentation jars
Different types of kimchi
Availability of kimchi products in North American supermarkets
Kimchi in malleable plastic packaging
Kimchi in hard plastic packaging
Personal kimchi refrigerator in residential unit
Overview of Ingredients and Instructions for Fermentation
The production of kimchi begins with the gathering of raw materials including:[3]
- Fresh vegetables (e.g. Chinese cabbage, radish, cucumber)
- Spices (e.g. red and black pepper, cinnamon, garlic, ginger, onion, mustard)
- Seasonings (e.g. salt, salt-pickled seafood, corn syrup, sesame seed, soybean sauce)
- Additional ingredients (e.g. mushrooms, seafood, cereals, fruits, meats)
The vegetable is washed, shredded, and soaked in a brine solution for 2-3 hours to draw out water and water-soluble vitamins.[3][4] This will allow the spices and seasonings to penetrate the vegetable better when they are added.[4] The water is then drained and the vegetable is mixed with other ingredients.[3] Next, the kimchi is fermented by cultures naturally present in the vegetables.[4] Depending on the time for consumption, the kimchi can be fermented at different temperatures. For short-term consumption, kimchi is fermented at room temperature for 1-2 days and for long-term consumption, kimchi can be fermented at lower temperatures to retard fermentation.[3][4]
The Science Behind the Fermentation Process
Bacteria and Probiotics Involved
The prevailing microorganism involved in kimchi fermentation is lactic acid bacteria (LAB).[1] They are initially present in low amounts in raw vegetables and seasonings as part of the microflora, but the environment can be controlled to favour their growth.[1] The conditions include storing the fermenting kimchi in low temperatures, the presence of 1.5-4.0% sodium chloride, and creating an anaerobic environment.[1]
The different strains of LAB develop sequentially owing to the changing environmental conditions that arise during fermentation.[1] The initial dominant genera of LAB is Leuconostoc.[1] As the pH and oxygen level of the environment decreases due to the metabolic actions of the bacteria, genera Lactobacillus, and Weissella become more dominant.[1] Minor communities include the Lactococcus and Pediococcus genera.[1]
Apart from the production of lactic acid, LAB also serves as a probiotic by synthesizing gamma-aminobutyric acid, a natural brain relaxant.[1] Further, LAB produces vitamins, which are essential nutrients that help body cell development and the immune system.[1] LAB also provides antioxidant and anticancer properties while inhibiting growth of pathogens.[1]
It is interesting to note that starter cultures are not typically used due to the high rate of failing to outcompete the naturally occurring LAB.[1] Therefore, the conditions mentioned (low temperatures, salt, and anaerobic conditions) have to be considered when creating a a starter culture for kimchi fermentation.[1]
The Chemistry
The fermentation process can be divided into four stages based on the acidity production.[3] The beginning stage has an acidity less than 0.2%.[3] The acidic levels increase in the immature stage, with a range between 0.2-0.4%.[3] The optimum-ripening stage has an acidity of 0.4-0.9%.[3] In the last level, the rancid (over-ripening) stage, kimchi will have an acidity greater than 0.9%.[3] In each of the different stages, specific LAB dominate and give kimchi its distinctive flavours due to the different acids produced.[1]
On a biochemical level, LAB produces various compounds such as organic acids, carbon dioxide, ethanol, vitamins, bacteriocins, prebiotic factors, and flavouring compounds like mannitol and amino acids under anaerobic conditions.[1] Lactate and acetate are the major organic acids, but other organic acids like propionic acid, butanoic acid, and fumaric acid are also synthesized.[1] Mannitol, a sugar alcohol that imparts a refreshing taste, is also produced during fermentation as a product of fructose reduction.[1]
Packaging and Maintaining the Quality
Packaging
Packaging of kimchi focuses on the protection of the kimchi from damage, easy accessibility, retainment of fermentation benefits, quality maintenance, shelf life extension, and provision to consumers with all the necessary nutrient and ingredient details.[5] Plastic is an excellent material in terms of cost, sturdiness, resistance to damage, and its grease and wetness barrier attributes.[6] The clear plastic also allows the consumer to see the product they are purchasing. Hence, kimchi is packaged most commonly in plastic containers, but can also be found in plastic pouches, trays, glass bottles, and metal cans.[6]
To distinguish themselves, many companies are creating product packages with a lid imitating a traditional Korean kimchi storage jar called an Onggi.[6] An Onggi consists of a heavy clay or stone lid which presses down on the kimchi to submerge it into the fermentation liquid while also allowing air to pass through the pores of the clay.[6] This enhances the kimchi flavour, prevents discoloration, and sustains quality, thus these product packages are a well-liked choice among kimchi consumers.[6]
Storage
Kimchi is usually stored either for 3 weeks at 4°C or for 3-4 days at room temperature (higher temperature speeds up the fermentation process).[3] During distribution and storage, the fermentation process by LAB continues, potentially leading to over-fermentation of the kimchi.[3] Over-fermentation results in excessive acidification due to the continuous production of acids by LAB and decreased kimchi quality.[3] The kimchi will suffer increased sourness, softening of texture, and the diffusion of colour.[3] Therefore, the extension of kimchi shelf life and quality maintenance still poses as a major concern for the kimchi industry.[3]
Summary of Preservation Methods
1) Low temperature: Storing kimchi at low temperatures also delays or inhibits growth of thermophillic/mesophillic spoilage and disease-causing bacteria.[1][3]
2) Anaerobic conditions: Anaerobic conditions inhibits growth of aerobic microorganisms (moulds, yeasts, and some bacteria).[1]
3) Microbial antagonism: Byproducts of cellular metabolism of LAB
- i) Bacteriocins prevent spoilage and the growth of disease-causing bacteria.[1]
- ii) Organic acids (like lactic acid) lowers pH to inhibit growth of acid-intolerant microorganisms.[7]
4) Antioxidant: Helps reduce free radical damage by inhibiting oxidation.[1][8]
Potential Health Benefits & Risks
Health Benefits
In addition to containing probiotics, kimchi has a number of properties that benefit the health of the consumer.[9] Kimchi is a good source of fibre, vitamins (C and B), and minerals (sodium, calcium, potassium and iron).[9] Kimchi also has anticancer, antioxidant, and immune boosting attributes.[9] The anticancer action of kimchi stems from chemical compounds beta-sitosterol, thiocyanate, and linoleic acid which promote regulation of inflammation in the body as well as antimutagenicity.[9] Kimchi is shown to have the strongest anticancer results in the optimal ripening stage and when additional anticancer ingredients (e.g. mustard leaf) are added.[9] As an antioxidant, Kimchi removes free radicals, reducing the risk of oxidative stress occurring in the body.[9] Free radicals are oxygen molecules with extra electrons that may become imbalanced and cause oxidation in the body.[8] This can have many negative health effects, potentially leading to diabetes, cancer, and other health issues.[9] Kimchi contains many antioxidants including vitamin C, chlorophyll, carotenoids, and dietary fibres which help maintain the balance of free radicals in the consumer.[9]
Potential Risks
Despite the health benefits kimchi may provide, it has been shown that there may be some risks with consuming large amounts of kimchi, especially if individuals are consuming kimchi that has large amounts of salt. The article by Seung-Min Lee et al. suggests that rats being fed kimchi in addition to their regular meals had increased blood pressure when measured over 6 weeks. On the other hand, low sodium kimchi supplementation did not have this effect, and when the kimchi addition rats were supplemented with the low sodium version of kimchi, they still had hypertension.[10]
Additionally, although kimchi can have anticancer actions, some studies show that consumption of kimchi among individuals with certain genetic polymorphisms is linked to an enhanced risk of gastric cancer. As kimchi is exceedingly popular among Koreans, the risk of gastric cancer due to eating kimchi is relatively higher among Korean people.[11]
Potential Exam Question
Answer: In lecture 9 we learned about lactic acid bacteria being the primary microorganism responsible for fermentation of kimchi. We also know from lecture 9 that fermentation with lactic acid bacteria leads to production of lactic acid and thus the pH would decrease as fermentation proceeds. Further, we have learned in lecture 9 that fermentation can decrease the pH due to other types of acid produced by bacteria, such as propionic acid and acetic acid. These two key pieces of information together should make students realize pH would decrease as opposed to increase when "fermentation goes through several acidity levels". Although we cannot discount the usage of additional microorganisms, such as anaerobic or aerobic, we can make an educated guess that lactic acid bacteria may not be the only bacteria present. This means that both anaerobic and aerobic bacteria may be present in an enclosed space and therefore the oxygen availability decreases as fermentation is prolonged (lecture 5). Although brine is used to help draw out moisture, it would not help in drawing out vitamins A, D, and E because these are fat soluble vitamins (lecture 2 and 9). As indicated in lecture 5, higher temperatures would lead to faster rate of reactions until an optimum is achieved where further increases in temperature would lead to decreased reaction rates due to inactivation of microorganisms or enzymes.
Using all of the above reasoning, we would select A, C, and E as our final answer.
These are all important concepts that we have learned about in FNH 200 and this question makes students think about how to synthesize some of the knowledge we have gained and to apply it to real life situations.
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 Jung, Ji Young (November 8, 2013). "Kimchi microflora: history, current status, and perspectives for industrial kimchi production". Applied Microbiology and Biotechnology. 98: 2385–2393.
- ↑ Noh, Bong-Soo (December 4, 2015). "Regulating Safety of Traditional and Ethnic Foods". Regulating Safety of Traditional and Ethnic Foods: 369–380 – via Science Direct.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 Patra, Jayanta K.; et al. (September 28, 2016). "Kimchi and Other Widely Consumed Traditional Fermented Foods of Korea: A Review". Frontiers in Microbiology. 7: 1493. doi:10.3389/fmicb.2016.01493. Explicit use of et al. in:
|last2=(help) - ↑ 4.0 4.1 4.2 4.3 Bunning, Marisa (January 6, 2016). "Understanding and Making Kimchi" (PDF). University of California. Retrieved August 14, 2021.
- ↑ Codex Alimentarius (2017). "Standard for Kimchi CXS 223-2001" (PDF). Food and Agricultural Organization of the United Nations. Retrieved August 15, 2021.
- ↑ 6.0 6.1 6.2 6.3 6.4 Jeong, Suyeon (December 2016). "Kimchi Packaging Technology: An Overview" (PDF). Korean Journal of Packaging Science and Technology. 22: 41–47.
- ↑ Skura, Brent; Liceaga, Andrea; Li-Chan, Eunice; et al. (June 24, 2020). "9.3.5 Factors Affecting Fermentation in Foods". UBC Wiki. Retrieved August 15, 2021. Explicit use of et al. in:
|last=(help)CS1 maint: multiple names: authors list (link) - ↑ 8.0 8.1 Vijaya Chavan Lobo; et al. (July 2010). "Free radicals, antioxidants and functional foods: Impact on human health". Pharmacogn Rev. 4(8): 118–126. – via PMC. Explicit use of et al. in:
|first=(help) - ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 Park, Kun-Young (January 23, 2014). "Health Benefits of Kimchi (Korean Fermented Vegetables) as a Probiotic Food". Journal of Medicinal Food. 17: 7–14.
- ↑ Lee, Seung-Min; et al. (2012 August 12). "Effects of kimchi supplementation on blood pressure and cardiac hypertrophy with varying sodium content in spontaneously hypertensive rats". Nutrition Research and Practice. 6(4): 315–321. Explicit use of et al. in:
|first=(help); Check date values in:|date=(help) - ↑ Nan, Hong-Mei; et al. (2005 June 7). "Kimchi and soybean pastes are risk factors of gastric cancer". World Journal of Gasteroenterology. 11(21): 3175–3181. Explicit use of et al. in:
|first=(help); Check date values in:|date=(help)