Table of Contents
Kimchi is the most important traditional fermented food in Korea and one of the most widely consumed in other East Asian countries like Japan and China. Information about kimchi can be retrieved from the ancient Korean book “Samkuksaki,” published in 1145 A.D., as well as in many other documents such as the subsequent “Naehun,” “Hunmongjahoe,” “Sinjeung–yuhap,” and “Kanibuckonbang” (Cheigh and Park, 1994; Jang et al., 2015; Yang H. J. et al., 2015). According to them, kimchi was considered as the outcome of a simple vegetable in brine fermentation prepared in a stone jar (Cheigh and Park, 1994). Since then, several kimchi types have been recorded according to variations in their composition or preparation method (Surh et al., 2008). In that sense, kimchi prepared with the use of leaf mustard, sweet potato, radish or young radish with leaves (Dongchimi, Chonggak, Beeneul), dropwort, various wild grasses, lettuce (Gotchorri), cucumber (Sobagi, Ggagduki), eggplant, pumpkin, burdock, sliced vegetables (Nabak), leek, scallion, garlic, chicken, pheasant, ear shell, green laver as well as seafood are available in local markets of the Korean peninsula (Figure 1).
Kimchi ingredients and preparation
The wide variety of raw materials used for kimchi preparation makes it unique among the products for the production of which lactic acid fermentation is employed. This variety generates an array of products with escalating organoleptic intensity, which makes it suitable for every age and taste.
The raw materials are divided into four classes (Cheigh and Park, 1994): (a) major raw materials, (b) spices, (c) seasonings, and (d) other additional materials. Although Chinese cabbage is more often reported as the major ingredient, as many as 30 different types of vegetables, including radish, young Oriental radish, ponytail radish, and cucumber may be used as well (Kim et al., 2012). The spices regularly used include red and black pepper, cinnamon, garlic, ginger, onion, and mustard. The seasonings most frequently used include salt and salt-pickled seafood, corn syrup, sesame seed, and soybean sauce. Finally, mushrooms as well as vegetables such as carrot, leek, and water cress, seafood like oyster and shrimp, cereals like barley and rice, fruits like apple and pear, meats like pork and beef and many more depending upon availability, geographical region and desired taste fall into the last class of ingredients. Qualitative and quantitative variation in the aforementioned ingredients is reflected in the sensorial properties of the final product; in that sense, adjustment of the taste is feasible. The Chinese cabbage kimchi, locally referred to as “Baechu,” is the most popular type of kimchi in Korea. For the preparation of this product the average composition of the different raw materials is as follows: Chinese cabbage 74–90%, radish 2.8–13.5%, garlic 1.4–2.0%, ginger 0.5–1.0%, onion 1.5–2.0%, green onion 1.0–3.5%, red pepper 1.8–3.0%, and a wealth of optional ingredients such as leek, shrimp and anchovy paste etc. each added below 2.0%; the final salt level is calculated at 2.5% (Park et al., 1994; Cho, 1999; Park and Cheigh, 2003; Lee et al., 2005; Cho et al., 2006).
In Figure2 the basic preparation method is described. Initially, all raw materials are collected. Their selection depends upon taste preferences, availability of raw materials, family tradition, social status etc. Chinese cabbage, the major ingredient, is trimmed to small pieces and thoroughly washed. The excess water is drained and brining takes place. During brining, a small amount of table salt is added and left for 2–3 hours. During this time, washing, grading, cutting and mixing of the remaining raw materials takes place. When brining is completed, the excess amount of water is drained again and all the raw materials are mixed (Cheigh and Park, 1994; Park et al., 2014). Fermentation conditions depend upon consumption and storage needs; short-term consumption requires fermentation at room temperature whereas longer storage times requires fermentation at low temperature (5°C). The product can be called as kimchi only after the completion of the fermentation process (Kim et al., 2012; Oh et al., 2014).
Commercial production of kimchi
Kimchi has become one of the most important globally popular food products, because of its taste and health claims; therefore its market has increased worldwide (Jung et al., 2014). The major challenge regarding industrial kimchi production is obtaining uniform quality. This task may be achieved by careful standardization of the whole production procedure, i.e., use of high quality raw materials, starter cultures and suitable fermentation conditions. Due to the large number of health claims, a large proportion of which is attributed to the microbiota itself (see paragraph “health benefits”), the criteria for the selection of starter cultures include the evaluation of the medicinal potential. In that sense, LAB such as Ln. mesenteroides, Ln. citreum, and Lb. plantarum have been successfully applied as starter cultures for kimchi preparation (Kim et al., 2012; Ryu et al., 2012). However, the adaptability to the kimchi microenvironment that may be assessed through persistence, as well as technological properties, such as production of organic acids, mannitol, compounds that may affect the product organoleptically, biogenic amines, vitamins, and bacteriocins should also be considered (Lee et al., 2011, 2015; Jung et al., 2014).
Storage and preservation
The Korean made kimchi requires less quantity of salt due to the use of red pepper powder (Oh et al., 2014). As a result, kimchi can be stored for long periods of time facilitating commercialization that has increased sharply in countries like Korea, China, Japan, and the United States due to their popularity among the people (Kim et al., 2012). Kimchi is usually stored in two ways, either for 3 weeks at 4°C, which is considered as well ripened or for only 3–4 d at room temperature. The raw kimchi is eaten in various ways as salad mixed with sesame seeds, sesame seed oil and sugar, while the over-ripened kimchi is usually boiled with meat (jigae). It has been reported that the average consumption of kimchi for the Korean population on daily basis is 124.3 g, with maximum of 154.5 g consumed in the age group 30–49 years old (Surh et al., 2008). The most important problem in the commercialization of packaged kimchi is the continuous fermentation process by LAB during distribution and storage that eventually decreases significantly the quality of the product. Over-fermentation of kimchi results in excessive acidification (sour taste) due to the production of acid by LAB with softening of its texture and diffusion of color (Cheigh and Park, 1994; Lim et al., 2001). Thus, the extension of kimchi shelf life and maintaining of its quality by minimizing LAB growth, is a major concern for the kimchi industry (Swain et al., 2014).