Factors Affecting Kimchi Fermentation

Japanese Journal of Lactic Acid Bacteria Copyright (C) 2003, Japan Society for Lactic Acid Bacteria Review Factors Affecting Kimchi Fermentation Mheen, Tae Ick Korea Institute of Science and Technology Information 206-9, Cheongryangri-dong, Dongdaemun-ku,Seoul 130-742, Korea Abstract Kimchi is a Korean fermented food that is prepared through a series of processes including pretreatment of Chinese cabbage, salting, blending with various spices and other ingredients, and fermentation. The characteristics of kimchi differ depending on the kimchi variety, raw materials, processing methods, and fermentation conditions. Kimchi fermentation is initiated by the various lactic acid bacteria (LAB) present in the raw materials. Sugars in raw materials are converted to lactic acid, acetic acid, carbon dioxide, and ethanol by hetero and homo fermentative LAB during kimchi fermentation, along with other chemical changes. Many phys- icochemical and biological factors influence kimchi fermentation. This review covers in some detail the factors affecting kimchi fermentation. Key words: kimchi, fermented vegetable foods, lactic acid bacteria, lactic acid fermentation I . Introduction kimchi with water), dongchimi (whole radish kimchi with water) and nabak-kimchi (cut radish Kimchi is a Korean fermented vegetable food and Chinese cabbage)." that are salted, blended with various ingredients The raw materials used for kimchi preparation and fermented for a certain period of time at ambi- are divided into three groups, major, sub- ent temperature. The characteristics of kimchi dif- ingredients (spices) and optional ingredients. A rec- fer depending on the variety of kimchi. The ipe for the simplest kimchi may include cabbage varieties result from the raw materials used, proc- 100g, garlic 2g, red pepper powder 2g, green essing methods, season, geographic area and the onion 2g, and ginger 0.5g, with an optimum salt functional properties of kimchi. More than 200 content of 2-3% .2) kinds of kimchi are available in Korea, but The optimum pH for the best taste of kimchi is kimchi can be classified into two major groups: or- 4.2-4.5 with an optimum acidity of 0.6-0.8% as lac- dinary and mu/-kimchi (water-kimchi). Ordinary tic acid. The best taste is attained after 2-3 days kimchi without added water includes baechu- of fermentation at 20 °C with 2-3% salt. Kimchi kimchi (diced Chinese cabbage), tongbaechu-kimchi has a unique sour, sweet, carbonated taste and (whole Chinese cabbage), yeolmoo-kimchi (young usually is served cold. Also, kimchi contains, a oriental radish) and kakdugi (cubed radish large amounts of live lactic acid bacteria (LAB). kimchi). Mu/-kimchi includes baek-kimchi baech u In this respect, kimchi differs from Western sauer- kraut and Japanese asatsuke. The former is only To whom correspondence should be addressed. acidic in taste (therefore lacking the complex taste Phone : +82-2-3299-6231 of kimchi) and is served warm, while the latter is Fax : +82-2-3299-6234 not a fermented product and contains few live E—mail : [email protected] — 56 — Vol.14, No. 2 Japanese Journal of Lactic Acid Bacteria LAB. been reported in reviews and books." The total kimchi production was estimated to In general the factors that affect kimchi fermen- be 1,500,000 M/T in 2000 and one fourth of the tation are microorganisms, temperature, salt con- kimchi consumed was commercially produced. Ac- centration, fermentable carbohydrates, other nut- cording to a national survey, an adult consumes rients, any inhibitory compounds present in the 50-100g/day of kimchi in summer and 150- raw materials, oxygen and pH. In this review, 200g/day in winter!) the salts and salting conditions, temperature, raw During the past 50 years, many species of bacte- materials, natural preservatives and selected start- ria, yeasts, and fungi have been isolated and re- er cultures related to kimchi fermentation will be ported from kimchi samples. The major micro- discussed in detail. organisms responsible for kimchi fermentation are LAB and yeasts which are known to be responsi- II. Factors affect on kimchi fermentation ble for the softening of kimchi texture and the off flavor. The major species of LAB isolated and 1. Salts and salting conditions identified from kimchi are Leuconostocmesente- The concentration of salt is one of the key fac- roides, Leuconostoc dextranicum, Leuconostoc cit- tors for controlling kimchi fermentation and pres- reurn, Lactobacillus brevis, Lactobacillus fermen- ervation at various temperatures. There are more turn, Lactobacillus plantarum, Pediococcus pen to- than 200 kinds of kimchi available in Korea. How- saceus, and Streptococcus faeculis.' ever, the salt concentrations of these kimchi all dif- The sugars present in the raw materials are con- fer depending on the maker. A flow-chart for verted to lactic acid, acetic acid, carbon dioxide processing baechu-kimchi is shown in Fig.1. and ethanol by hetero fermentative LAB during Prior to kimchi preparation the major raw mate- kimchi ripening, and these acids and carbon diox- rials such as Chinese cabbages and radishes may ide are responsible for the fresh and carbonated be salted with either a salt solution (brine meth- taste of kimchi. However, after a certain period of od) or dry salt (direct addition method) and wash- time excessive lactic acids are formed and undesir- ed with clean water. This treatment is the most able flavors develop due to the growth of homo important step for fermentation and maintenance fermentative LAB and yeasts.1.2) of kimchi quality. It has been reported that the op- In the kimchi fermentation system, the hetero timum salt concentration for kimchi is about 2.0- fermentative LAB producing organic acids and car- 3.0%, while appropriate level is determined by bon dioxide from sugars are major species in the individual experience.2) Therefore, it is necessary early stage of fermentation, and homo fermen- to optimize the salting condition. Of the two salt- tative LAB producing excessive lactic acid are ing methods, the direct addition method is most major species in the late stage of fermentation. It widely used at the household level, but has the dis- has also been shown that low salt concentration advantage of being difficult to control the final and low temperature (eg, 2% and 10 °C ) favor salt content of the kimchi. The brine method is growth of hetero fermentative LAB, while high preferable for commercial production of kimchi. A salt concentration and high temperature (eg, 3.5% satisfactory quality for kimchi can be obtained and 30 °C ) favor growth of homo fermentative when the cabbage is salted for 3-6 hours using 15 LAB. Therefore, salt concentration and tempera- to 20% salt solution.' ture are the key factors for controlling kimchi fer- Salting is carried out over a range of time mentation!' from 3 to 15 hours depending on the salt concen- Besides the above mentioned key factors for con- tration, temperature, variety, cutting method and trolling kimchi fermentation, many other factors size of the cabbage. For baechu-kimchi, the final such as the raw materials, processing methods, salt concentration is adjusted to 2.0-3.0% of the and natural preservatives and starters which af- overall ingredients, this concentration being best fect kimchi fermentation and preservation have for optimum fermentation. This concentration is —57--- Jpn. J. Lactic Acid Bact. Vol.14, No. 2 Fig.1. Flow-chart for production of baechu - kimchi. Fig.2. Changes of total acid during kimchi fermentation at different temperatures and salt concentrations. — 58 — Vol.14, No. 2 Japanese Journal of Lactic Acid Bacteria maintained during fermentation and preservation. 6.3%. The pH level reduced during the fermenta- If the salt concentration is below the optimum con- tion, while the total acid content of dongchimi in- centration, fermentation proceeds too quickly and creased and the salt concentration of the can cause excessive acidification and softening. dongchimi liquid decreased. Equilibrium for the On the other hand, color and flavor are not accept- salt concentration between the dongchimi liquid able when the salt concentration is over 5%.2)De- and the solid radish was achieved after 15-22 days pending on the salting time, free sugars and of fermentation. Vitamin C and the reducing amino acids are reduced in raw cabbage and the sugar content of the dongchimi liquid and Chinese texture, chemical and physical properties, and radish increased until 15-22 days of fermentation, total microbial counts change during saltine') and then decreased. Salt concentration had a sig- Generally, salting reduces the moisture content nificant effect on the sensory properties of (10-12%),relative volume, and weight, as well as dongchimith) the internal void space of the cabbage. These Recently, to examine the quality of mu]-kimchi, changes affect the physical properties of the vege- the temperature (4, 15, and 25°C for 10 days) and table, especially the flexibility and firmness of the salt concentration (0, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, and tissue, which gives a distinctive textural property 3.0%) in water was conducted, and it was found to the final product. As a result of brining, the that the pH was the lowest and the acidity the total amount of microorganisms, such as aerobic highest in the in u/-kimchi containing 1.0% salt. counts, in salted cabbage are reduced (11-87%), The total vitamin C content in mui-kimchi contain- and LAB increase (3-4times). The amount of reducing 3.0% salt was higher than in the low-salt sam- ing sugars also decreases. (7-17%)7,11) ples after the optimum ripening time and the Washing conditions for salted cabbage is also im- overall palatability of mui-kimchi showed the high- portant for quality preservation of the kimchi.'2) est score in the 1.0% salt sample.16) Chinese cabbage treated with a 1000 ppm solution of grapefruit see extract or citric acid at 10°C 2.

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