Factors Affecting Kimchi Fermentation

Review

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 physicochemical 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 sauerkraut 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]

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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

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Fig.1. Flow-chart for production of baechu - kimchi.

Fig.2. Changes of total acid during kimchi fermentation at different temperatures and salt concentrations.

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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. Temperature shows a retarded increase in titratable acidity and After salt concentration, the most important fac- a decrease in pH and reducing sugar concentra- tor affecting kimchi fermentation is temperature, tion.". Kimchi made from Chinese cabbage soaked since the kimchi fermentation occurs mainly by in a heated 10% salt solution at 40°C has im- the microorganisms naturally present in the raw proved quality and shelf-life.' materials. Kimchi is now available year-round but Fig.2 shows the effect of salt concentration and the quality of .kimchi differs depending on geo- temperature on acid production during kimchi fer- graphical location and season. Ambient tempera- mentation.H)Total acid was more at lower salt con- ture is used for making kimchi for personal concentration (2.25%)than at any temperature tested sumption. Kimchi fermentation and over acidifica- for high concentration. At the lower salt concen- tion occurs simultaneously at ambient tempera- tration, maximum acidity was reached in a ture. shorter period of time. At 30°C and 2.25-3.5%salt Fig.3 shows the changes of pH and total acids concentration, the acidity of kimchi was main- during kimchi fermentation at various tempera- tained in the same pattern throughout. An acidity tures. Ripening time of kimchi depends on the fer- of 1.55% was reached in 5 days and was main- mentation temperature, therefore differences in pH tained at 1.6% thereafter, but at 5.0 and 7.0% and acidity were seen. At 20°C , the pH dropped salt concentration, the acidity reached 1.4 and sharply with increasing acidity, but pH and acid- 1.1% after 5 and 6 days, respectively. ity at 10°C changed more slowly than at higher The effect of salt concentration on dongchimi temperatures. (ponytail Chinese radish kimchi) fermentation was Maximum total acid produced in kimchi at 20°C also studied's). Diced Chinese radishes were fer- and 15°C is 1.6%, but never exceeds 1.2% at 10°C. mented at 4°C with a salt concentration of 1.5- A panel evaluation determined that the pH and

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acidity of the optimum ripening period for kimchi Chemical changes, LAB and yeast counts in were 4.2-4.5 and 0.6-0.8% (as lactic acid), respec- kimchi prepared by commercial manufacturers in tively.') large scale were monitored at different fermenta- The optimum ripening time and the edible pe- tion temperatures. It was confirmed that the opti- riod for kimchi varied depending upon the fermen- mum pH of kimchi is around 4.2 which was tation temperature and salt concentration as reached within 2 days at 25 °C , 3 days at 15 °C , shown in Table 1. At 30°C, the optimum ripening and 23 days at 5°C fermentation, respectively. 17) period was 1 day and the edible period was 1-2 Differences in the quality characteristics such as days. At lower temperatures, the optimum ripen- pH, acidity, reducing sugar content, microbial ing time and the edible period were longer than counts and sensory properties between whole Chi- at higher temperatures. At 5°C and above 5.0% nese cabbage kimchi (pogi -kimchi) and sliced Chi- salt concentration, kimchi ripened very slowly and nese cabbage kimchi (ma t-kimchi) were examined at 7.0% salt concentration it did not ripen even during fermentation at 20°C for 10 days and 5°C after 180 days fermentation. 14) for 50 days. Pogi-kimchi showed a slower fermen-

Fig.3. Changes of total acid and pH during kimchi fermentation at various temperatures.

Tablel. Optimum ripening time and edible period of kimchis

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tation, approximately 2 days at 20°C and 10 days LAB, dissolved carbon dioxide content, reducing at 5 °C , than mat-kimchi. Odor, color and flavor sugar content and temperature at the center of scores for the kimchi were higher in the samples kimchi jars were measured . The pH and the fermented at 20 °C than those fermented at 5 °C , total acid content of kimchi that was fermented also there were no great differences in the sen- at 17°C for 4 days were almost the same as those sory properties of pogi-and mat-kimchi. The gas of kimchi fermented at 4°C for 48 days. The total composition of the packages containing the kimchi cell counts of microorganisms and LAB in kimchi fermented at 20°C showed increased CO2 concentra- which were fermented at 17°C for 2 days and 4°C tion and decreased 02 concentration after 3 days for 9 days were 1.5 X 109 and 6.3 X 108 cells/m/, and for both kimchi varieties.' 2.0 x 108 and 8.7X 107 cells/m/, respectively. The re- The effect of fermentation temperature on the sults showed that it took 23 and 35 hr, respec- sensory, physicochemical and microbiological prop- tively, to reach the temperature of 17°C and 4°C erties of kakdugi (cubed radish kimchi) and on at the centers of a jars during bulk fermentation the free sugar, organic acid and volatile com- of kimchi from an initial temperature of 12°C. 21) pound levels in kakdugi during fermentation were The characteristics of natural lactic acid fermen- also investigated. '9.2°)After initial fermentation for tation using radish juice were investigated at dif- 12, 24 and 36 hr at 20°C, kakdugi was fermented ferent salt concentrations (0-2%) and temperatures for 57 days at either 4 °C , 10°C or 20 °C , respec- (10-30°C) using low salt kimchi (a kind of water tively. The pH was decreased to between 4.1 and kimchi). It was found that the LAB isolated from 4.3 from the initial pH 5.8, and the total acidity in- radish juice fermented at 2% salt concentration creased 2-4 times that of the initial value (0.2%). was mainly Leu. mesen teroides, Lac. plan tarum The number of LAB remarkably increased in palat- and Lac. brevis. Growth rate of LAB increased able period and gradually decreased thereafter."' with increasing temperature at 1% salt concentra- Free sugar levels decreased at each temperature tion and the LAB was still active at 10 °C . The during fermentation (with the - exception of man- time required to reach pH 4.0 during fermentation nitol, levels of which increased) although decreases with juice containing 1% salt was 11-13 days at were less marked in samples fermented at 4t Of 10°C and 2-3 days at 30°C .22' the organic acids tested, lactic acid production The effects of fermentation temperature (0-15°C) was the most pronounced, increasing substantially and salt concentration (1.5, 2.75, 4.0%) on the fer- with time and temperature. In contrast, malic mentation parameters of kimchi were also ana- acid, which was the most abundant organic acid. lyzed by response surface methodology. The pH initially, decreased in concentration during fermen- decreased and acidity increased with increasing fer- tation, and this decrease was most pronounced at mentation time; while reductions and incremental higher temperatures. rates increased as temperature increased and salt Levels of the volatile compound, methyl ally' sul- concentration decreased. The optimum pH of 4.2 fide, were initially very low, but increased dramati- was achieved within 14-24 days at 5-15°C , but at cally up to approximately 45 days after which 5°C , the pH was still >4.2 after 24 days. Maxi- levels decreased. The increase corresponded to in- mum edible acidity (0.75%) was reached within 8 creased aroma in the sensory evaluations. These re- days at 15°C , but at 0°C , acidity was only 0.35- sults suggest that fermentation at 4°C , following 0.43% after 24 days of fermentation. Edible peri- an initial fermentation at 20°C for 36 hr, is suit- ods for kimchi, based on the acidity range 0.4- able for the production of good quality kakdugi 0.75%, were 4, 10, and 18 days for the fermenta- with high free sugar and organic acid contents.20) tion at -15, 10, and 5°C, respectively, at 2.75% salt In order to investigate the fermentation charac- concentration.") teristics of kimchi, which was made at 12°C and fermented at 17°C and 4°C, the pH, total acid con- 3. Raw materials centration, total cell counts of microorganisms, Kimchi, a fermented vegetable food with various

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components (including seasoning and spices), has extensively studied."-") been the most popular side dish served with Besides the temperature and salt concentration, cooked rice for hundreds of years in Korea. In the type of kimchi is also a factor in controlling total, there are about 200 kinds of kimchi, whose kimchi fermentation. Therefore, the three main raw materials are mainly Chinese cabbage and rad- types of Chinese cabbage kimchi, baechu-kimchi ishes. Dried red pepper powder, garlic, green and tongbaechu-kimchi (semi solid types of the cab- onion and ginger are the widely used seasonings. bage kimchi prepared with a large amount of hot The types and amounts of seasonings used in pepper powder and a small amount of water) and kimchi vary greatly between manufacturers and baek-kimchi (a liquid type of kimchi prepared processors. The quality and species of the major in- with a small amount of hot pepper powder and a gredients significantly affects fermentation and large amount of water), were selected as models the product characteristics of kimchi. to compare the fermentation characteristics of The important raw materials of kimchi are di- kimchi. The amount of hot pepper powder and vided into three groups: the major raw materials, water are believed to be the primary (or external) sub-ingredients (spices) or fermented fishery prod- and secondary (or internal) factors, respectively, af- ucts, and optional (minor) ingredients. fecting kimchi fermentation.') As seen in Table 2, Chinese cabbage is the most The growth of microorganisms can be controlled common major raw material for preparing kimchi by the appropriate addition of raw materials. while radishes are used for kakdugi (cubed radish Among the sub-ingredients, hot pepper powder,29-32) kimchi) and dongchimi (whole radish kimchi with radishes,34) fermented anchovy and shrimp,'") water) preparation. Cabbage, whole radish, cucum- starches,35.3" reducing sugar,"A soluble solids,' and ber, mustard leaves, green onion, and leeks which protein sources')have been probed for their abil- are available in different seasons and localities are ity to promote kimchi fermentation, but garlic, the raw materials used for making special kimchi leaf mustard and leek have been shown a have de- in Korea. laying effects,"."-") while green onion and ginger One of the important criteria for making the have controversial. effects on kimchi fermenta- good taste of kimchi is the selection of good qual- tion."-') ity raw materials, followed by formulation of Garlic is used most frequently as a sub- kimchi ingredients and seasonings. ingredient (100%) in kimchi. Since ground garlic Table 3 shows the basic ingredients for making is used in kimchi making, alliin is changed to baechu-kimchi, kakdugi, dongchimi, and m ul- allicin which has an intensive taste. Allicin takes kimchi, but the most simple kimchi recipe includes part in fermentation of kimchi by inhibiting the salted cabbage 100 g, hot pepper powder 2 g, gar- growth of various unnecessary microorganisms de- lic 1.5g, green onion 2 g, ginger 0.5 g and final rived from sub-ingredients during the initial fer- salt concentration of 2-3%.14) mentation period and slows the fermentation of Generally softer texture and higher sugar con- kimchi. Garlic improves the storage capacity by tent vegetables are desirable for making good qual- prolonging the LAB fermentation period and re- ity and good tasting kimchi. However, hard sults in less a.cidification.29,30,2.43A6)With fermenta- texture vegetables are more favorable for long- tion of kimchi, the intensive hot taste of garlic term preservation without softening!' slowly changs to a harmonized taste and flavor.31) Among the many kinds of kimchi, baechu-kimchi The composition of pigments in hot pepper con- has been consumed for the longest time as a tradi sists of 40 different carotenoids, with capsanthin tional fermented vegetable food in Korea. The and capsorubin being the most widely found, and kind and amount of ingredients involved in carotenes such as provitamin A. The average baechu-kimchi preparation affect the kimchi fer- amount of hot pepper added to kimchi was found mentation rate. Effects of raw materials and ingre- to be 2.24% with a frequency of use of 97.3%. In dients on kimchi fermentation have been spite of the fact that hot pepper was reported to

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Table2. Raw materials used for kimchi preparation

Table3. Ingredient composition of various kimchi varities

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promote the fermentation of kimchi, it did not 4. Natural preservatives show any significant increase in sour taste and The groups of LAB involved in kimchi fermenta- did not affect sweetness, saltiness, palatability or tion continuously produce organic acids after the crispiness." optimum ripening, and cause changes in the com- Green onion and leek contain various allyl sul- position of kimchi. These changes are called over fides, carotenes and vitamin C. The frequency of ripening or over acidification, and are often ob- use in common cabbage kimchi was 72.8% for served in summer kimchi and winter kimchi green onion and 32.4% for leek, which both are stored for extended periods of time. Over ripening much lower than the 100% for garlic and 97.3% is the most serious problem for storage of for hot pepper. The amounts of green onion and kimchi. Since over acidification is mainly due to leek used for kimchi making are still high, ie, 0.6- the activities of lactic acid-producing LAB, the 0.9% for green onion and 2.0-6.0% for leek. Re- best way to overcome this is to control the cently, it has been reported that leek retards the growth of LAB without destroying the quality of fermentation of kimchi due of its antimicrobial ac- the kimchi. tivity.") Screening of natural preservatives such as me- Ginger contains unique components like citral dicinal plants, edible plants, herbs and spices, and linalool, and hot spicy components such as antimicrobial agents and related compounds to in- gingerone and shogaol. Ginger causes a delay in hibit kimchi fermentation have been studied exten- fermentation and there were no significant differ- sively.° Among 42 oriental medicinal plants test- ences in the sourness, sweetness, saltiness, spici- ed, Baical skullcap barks (Scutellaria baicalensis), ness, palatability, unpleasant and overall tastes, and powders of Assam indigo (Baphicacanthus acidic odor and color between the kimchi fer- cusia) were very effective for preserving kimchi. mented with and without ginger.'" Among 32 herbs and spices tested, peppermint Fermented anchovy and shrimp contain large leaves (Mentha piperita L.), cinnamon barks amounts of proteins and amino acids, and have (Cinnamomum verum Presl), lemon balm leaves their own unique taste and flavor. Therefore, (Melissa officinalis L.), flower buds of clove (Euge- these sub-ingredients affect not only the nutri- nia caryophyllate Thunb.), hop leaves (Humulus tional balance but also the sensory quality of lupulus L.), rosemary leaves (Rosmarinus offici- kimchi. These fermented fish products and other nails L.), sage leaves (Salivia officinalis L.), horse protein sources such as skim milk, soy protein iso- radish roots (Moringa oleifera Lam.), and the late, beef extract, and fish protein produced high leaves and flowers of thyme (Thymus vulgaris L.) lactic acid concentrations and promoted the showed high antimicrobial activity against micro- growth of LAB."."'") organisms in kimchi. Clove was the most effective The frequency of addition of starch and sugar microbial inhibitor, when added to fresh kimchi. in kimchi making was 27% with a concentration. However, sensory testing was not appropriate for of 0.4-3.0%, and sugar was used for sweet and har- evaluation of the effect of herbs and spices, since monized tastes. However, since starch and sugar their highly specific flavors affect the taste of are utilized as carbon sources by various microor- kimchi. Among 28 fruits, vegetables and related ganisms present in kimchi, they affect kimchi fer- plants tested, the leaves of pine tree (Pin us mentation and sensory quality. In the results, rigida), persimmon (Diospyros kaki) and oak (Quer- starch and sugar promote the fermentation of cus glauca) also demonstrated significant bacteri- kimchi and contribute greatly to the harmony of cidal effects. In addition, of 21 natural preser- tastes by reducing the hot and overall tastes, as vatives added individually to fresh kimchi, only well as the acidic and garlic odors." It was also nisin and caffeic acid were able to inhibit fermenta- found that both wheat flour and glutinous rice tion.° flour hastened the fermentation of yulmoo- The changes of pH and acidity of baechu kimchi.") kimchi and mu] kimchi were remarkably inhibited

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by the addition the tea catechins to a level of of kimchi was studied during fermentation at 2mg/g fresh baechu, the results suggesting that 20 °C for 8 days. It was found that chitosan re- the tea catechins can be successfully used for ex- duced the total number of microorganisms and lev- tending the shelf-life of kimchi.48) els of Leuconostoc species and Lac. plantarum in Studies were carried out to investigate the ef- kimchi, and the lower molecular weight chitosan fects of Lithosperrnurn erythrorhizon and Gly- fraction had the greatest effect on the levels of cyrrbiza uralensis (LG), both with and without Leuconostoc species. Also, chitosan reduced the in- dipping salted Chinese cabbage in 1% chitosan so- tensity of sour and stale flavor in kimchi, and lution (LGDC), on the fermentation of kimchi at the content of reducing sugar in control kimchi 10 °C for 25 days, The sour taste of LG and was lower than in the chitosan containing kimchi LGDC treated kimchi changed more slowly than for the first 6 days of fermentation at 20 °C. that of the control during fermentation. The shelf Malic acid content was lower and lactic and acetic life of LGDC treated kimchi was extended by acid content were higher for the control kimchi more than 10 days compared with the control." than for the chitosan containing kimchi for the By the addition of 1% mixed extract of Lithos- first 4 days of fermentation. Control kimchi con- permurn erythrorhizon and Scutellaria baicalensis tained more succinic acid than the chitosan con- and 1% crab shell treated with ozone to kimchi, taining kimchi for the first 2 days of color, flavor, and sourness were negatively ef- fermentation!' Leuconostoc species and Lac, fected to a slight degree, while texture and over- plantarum were higher in the control than in the all acceptability were found to be the same or chitosan containing kimchi dissolved in 0.3% ace- slightly improved compared with untreated tic acid and 0.05% sodium benzoate.') It was also kimchi.') It was also found that the kimchi con- found that addition of chitosan to kimchi influ- taining. 2% ozone treated crab shell powders ences pectic substance levels and improves their showed both strong neutralization action for 0-25 textural properties.') days and buffer action after 25 days during fer- Two percent ginseng in kimchi had the best over- mentation at WC.") all preservability and quality, and promoted the Addition of 500 ppm grape fruit seed extract growth of Lac. plantarum and Lac. ferment= (GFSE)) showed the highest pH during fermenta- and inhibited the growth of Leu. mesenteroides tion at 20°C and the lowest titratible acidity corn- and Ped. cerevisiae.") pared with the control. The total microbial counts Addition of sap from pine needles (Pin us were higher than the LAB counts immediately fol- densiflora) delayed kimchi fermentation by slow- lowing the preparation of kimchi, but they were ing down the decrease in pH and inhibiting the similar after three days. However, sensory evalua- growth of Lactobacillus species!') tion of 3 day old kimchi samples showed a signifi- Water extract of pine needles had stronger in- cant difference (P<0.05) between the control and hibitory effects against Lac. plantarum than again- the treated kimchi (100, 300 and 500ppm) when st Leu. rnesenteroides.") evaluating odor, color and taste. Only the 50 ppm It was found that mustard oil had antimicrobial GFSE sample was found not to be significantly dif- effects on the major LAB of kimchi such as Lac. ferent from the contro1.52) plan tarum, Lac. brevis, Leu. mesen teroides and Recently, the fermentation characteristics of Ped. cerevisiae, and mustard powder (0.1%) and mustard leaf kimchi with added green tea and mustard oil (200 ppm) extended the shelf-life of pumpkin powder have been studied and it was kimchi, after 15 days storage at 15t.60) found that the sensory scores for flavor, aroma The extract of bamboo leaves had a wide range and overall acceptability were highest in the of antimicrobial activity against Brettanomyces kimchi with 0.3% pumpkin powder and 0.2% custersii, Klebsiella oxytoca, Pichia membranae- green tea powder.") faciens which cause kimchi softening5 Recently, The effect of chitosan (0.5%) on the properties the effects of cuttlefish bone (Sepiae os),') enoki

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mushroom (Flammulina velutipes),' Monascus cells/nil). koji," and boiled-dried edible seaweed (Hizikia fusi- A hetero fermentative type of LAB, Leuconostoc forme)65 on the fermentation and quality of mesenteroides, is a major bacterial component of kimchi have been studied. kimchi from the initial to the middle stage of fermentation. During these stages, hetero fermenta- 5. Starters tive type LAB produce various metabolites such The quality of kimchi can controlled by desir- as lactic acid, acetic acid, ethanol, carbon dioxide, able microorganisms, and various fermentation mannitol, and dextran which are associated with conditions such as temperature, salt concentration, the taste of kimchi, and the number of LAB and nutrients in raw materials. As already men- reaches its maximum during the optimum ripen- tioned, kimchi fermentation and ripening are car- ing period. However, total number of Leu. ried out by the microorganisms present in the mesenteroides decreases sharply when the pH of raw materials. Sugars in raw materials are con- kimchi is decreased to 4.0. On the other hand, a verted to lactic and acetic acid, carbon dioxide, homo fermentative type LAB, Lac. plan tarum, ethanol and mannitol by the LAB growing at 1- which has a strong pH tolerance under high or- 3% salt concentration. The total count of kimchi ganic acid concentrations, continuously increases microorganisms reaches its maximum level (1 X 10" in count during kimchi fermentation to the last cells/m4 at optimum ripening time, after which stage. It has been reported that the acidification the number of LAB decreases slowly and main- of kimchi is mainly caused by Lac. plantarum.") tains what is called the 2nd maximum level (1 X 10' • As seen in Table 4, Lac. plantarum, Lac. brevis,

Table4. List of lactic acid bacteria and yeasts used as kimchi starters

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Lac. bavaricus, Lac. ho.mohiochli, Ped. cerevisiae, YK-19, that showed better growth at 10°C than at Leu. mesenteroides, Leu. dextranicum, Lea. 25°C in the medium containing 0.3% lactic acid paramesen teoides, and Sac.fermen tati were isolated and 0.6% acetic acid, was isolated from kimchi from kimchi and have been used as kimchi start- and used as a kimchi starter in order to prevent ers to improve the quality and shelf-life of over acidification of kimchi.') The addition of Sac. kimchi 66-71) fermentati YK-19 prolonged the period of opti- The combination of Leu. mesenteroides, Lac. mum fermentation (at pH 4.2 and 0.6-0.8 acidity) brevis, Lac. plan tarum and Ped. cerevisiae, all by >63%. The lactic acid content increased rapidly strains isolated from kimchi, have been used as in control samples, followed by the kimchi with starters for kimchi fermentation. These starters in- Sacharomyces sp. YK-17 and Sac.fermentati YK-19 crease the fermentation rate, and mixed strains as starters. The growth of Lactobacillus species are more effective than single strains in produc- was inhibited by the addition of yeast starter, par- ing better organoleptic quality kimchi." ticularly by Sac. fermentati YK-19. Furthermore, Generally, kimchi fermentation has been carried sensory evaluation scores for acidic and moldy fla- out at relatively at low temperatures, and psy- vor were reduced by starter addition, while scores chrotrophic LAB have been isolated and character- for freshness increased.'" ized from kimchi fermented at 5°C .24,67) Therefore, Lou. paramesen teroides P-100, a psychrotrophic psychrotrophic LAB isolated from kimchi.fer- mutant which grew well at pH 4.0, and 10°C, and mented at low temperature were studied as start- in an organic mixture (lactic acid:acetic acid;1:2) ers for their effect on kimchi fermentation. The was derived from the wild type Leu. results indicate that the fermentation period can paramesenteroides Pw. Kimchi with added mu- be shortened by use of LAB starters isolated tant strain P-100 had better taste than that of con- from low temperature kimchi. Among the LAB trol kimchi by the sensory evaluation test and the used as kimchi starters, it was shown that optimal pH range of kimchi extended up to about Leuconostoc species were more effective than any 2.2-2.5 times. In the kimchi added with Leu. other Lactobacillus species tested for kimchi fer- pararnesenteroides P-100 , the succinic acid content mentation." was higher than for that of the others tested, Because the acid production from the hetero and the total number of Lac. plantarum was re- fermentative type LAB is lower than that of the duced about 2.5 fold when compared to the con- homo fermentative type LAB, the addition of an trol kimchi.") acid tolerant mutant strain Leu. mesenteroides as Leu. mesenteroides M-100, an acid tolerant mu- a starter for kimchi fermentation may inhibit the tant derived from the wild type strain Leu. rapid pH decease and lactic acid production during mesenteroides Mw, and Sac. fermentati YK-19, an kimchi fermentation. Therefore, the mutant strain acid utilizing and aromatic flavor producing yeast, Leu. mesenteroides M-10, which could grow at low were tested for their ability to retard acidification pH (3.0) at 10°C and produced more CO2 than the and prolong of the edible period of kimchi."'") The wild type, was found to be a superior kimchi addition of Lea. mesenteroides M-100 to kimchi starter. With respect to total acceptability, the preparation may induce the prolonged acidification kimchi prepared using the mutant strain M-10 of kimchi because of its low production of lactic was better than the other strains, and use of the acid and increased growth in comparison with mutant strain extended the optimum ripening pe- Lac. plantarum. Also Sac. fermentati YK-19 may riod of kimchi by two fold compared with that of lengthen the edible period of kimchi by reducing the control. These results show that a mutant the content of lactic acid and acetic acid during strain of Leu. mesenteroides which is more stable the later period of kimchi fermentation, and the to growth in acidic conditions was able to extend superior flavor in the kimchi group treated with the edible period of kimchi." starters may be due to the various substances, car- Psychrotrophic yeast, Saccharomyces fermentati bon dioxide, and succinic acid produced by Leu.

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mesenteraides M-100 and Sac. ferrnentati YK-19.74) optimum temperature for kimchi fermentation is The inoculation with mutant strains of Leu. 10-15°C, and storage temperature should be under mesen teroides and Leu. paramesen teroides in- 5°C. Selection of good raw cabbage is another im- creased adipic acid resistance compared with the portant factor and addition of garlic, hot pepper, wild type species and its effect on the shelf-life of sugars and protein sources are also important for kimchi were evaluated. The combination of both making quality and good tasting kimchi. mutants was more effective than that of any sin- Many homo and hetero fermentative LAB, such gle strain in extending shelf life of kimchi. The op- as genus Lactobacillus, Leuconostoc, Weissella, timum inoculation was 0.005% of a 1:10 mixture Lactococcus, Streptococcus and Pediococcus were of Leu. mesen teroides: Leu. paramesenteraides ac- isolated and identified from various kimchi sam- cording to the results from acidification tests and ples, but genus Leuconostoc, Weissella and other sensory analysis.') LAB producing organic acids, carbon dioxide and bacteriocins are the most important microorgan- III. Conclusion isms for controlled fermentation of kimchi. Psychrotrophic and acid tolerant LAB, especially Kimchi has a unique taste characteristics having wild and mutant strains of the Genus Leuconostoc sour, sweet and carbonated tastes with medium and yeasts, Genus Saccharomyces, utilizing or- texture. In this respect kimchi differs greatly ganic acids and producing aromatic flavors could from sauerkraut that is popular in the West. The be applied as starters to control the fermentation optimum acidity, pH and salt concentration of and improve the shelf-life of kimchi. However, fur- kimchi are 0.6-0.8% (as lactic acid), 4.2- 4.5 and 2.0- ther studies are needed to understand the mecha- 3.0%, respectively. Kimchi 4rmented at lower tem- nism of these LAB and yeasts on kimchi peratures are superior in quality and taste to fermentation. those fermented at higher temperatures. After optimum ripening is reached, kimchi fer- Kimchi fermentation is complex and is due mentation may continue until the product has an mainly to certain LAB and yeasts naturally pre- acidic taste and softened texture, which is caused. sent in the raw materials. Several physicochemical the acid deterioration. Among the natural pre- and biological factors such as salt and sugar con- servatives tested for preservation and preventing • centration, temperature, raw materials, natural over acidification of kimchi, clove, tea catechin, preservatives and starter culture influence the qual- chitosan, oil of fruits and plant seeds were effec- ity of kimchi. Among the many factors affecting tive for controlling kimchi microorganisms and im- kimchi fermentation, salt content and temperature proving the shelf-life of kimchi, but high are the most important, followed by the quality concentrations of natural preservatives may cause of raw materials and microorganisms, typically an undesirable flavor in kimchi. The storage of hetero fermentative LAB and psychrotrophic kimchi at around 5°C is thought to be the best yeasts. way to ensure long-term preservation up to 6 The salting of the major raw materials of months. kimchi is a very important step for fermentation Finally, further research is needed to develop and for the quality of the kimchi. The optimum the technology necessary for controlled fermenta- salt concentration of kimchi is around 2.0-3.0%. tion using starters and for the long-term preserva- Under the optimum salt concentration, tempera- tion of commercial kimchi at ambient temperature is the next important factor for controlling ture. kimchi fermentation and preservation, The

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