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 ma-

terials, 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 de-

tail the factors affecting kimchi fermentation.

Key words: kimchi, fermented vegetable foods, lactic acid bacteria, lactic acid fermentation

I . Introduction

Kimchi is a Korean fermented vegetable food

that are salted, blended with various ingredients

and fermented for a certain period of time at ambi-

ent temperature. The characteristics of kimchi dif-

fer depending on the variety of kimchi. The

varieties result from the raw materials used, proc-

essing methods, season, geographic area and the

functional properties of kimchi. More than 200

kinds of kimchi are available in Korea, but

kimchi can be classified into two major groups: or-

dinary and mu/-kimchi (water-kimchi). Ordinary

kimchi without added water includes baechu-

kimchi (diced Chinese cabbage), tongbaechu-kimchi

(whole Chinese cabbage), yeolmoo-kimchi (young

oriental radish) and kakdugi (cubed radish

kimchi). Mu/-kimchi includes baek-kimchi baech u

kimchi with water), dongchimi (whole radish

kimchi with water) and nabak-kimchi (cut radish

and Chinese cabbage)."

The raw materials used for kimchi preparation

are divided into three groups, major, sub-

ingredients (spices) and optional ingredients. A rec-

ipe for the simplest kimchi may include cabbage

100g, garlic 2g, red pepper powder 2g, green

onion 2g, and ginger 0.5g, with an optimum salt

content of 2-3% .2)

The optimum pH for the best taste of kimchi is

4.2-4.5 with an optimum acidity of 0.6-0.8% as lac-

tic acid. The best taste is attained after 2-3 days

of fermentation at 20 °C with 2-3% salt. Kimchi

has a unique sour, sweet, carbonated taste and

usually is served cold. Also, kimchi contains, a

large amounts of live lactic acid bacteria (LAB).

In this respect, kimchi differs from Western sauer-

kraut and Japanese asatsuke. The former is only

acidic in taste (therefore lacking the complex taste

of kimchi) and is served warm, while the latter is

not a fermented product and contains few live

To whom correspondence should be addressed.

Phone : +82-2-3299-6231

Fax : +82-2-3299-6234

E—mail : [email protected]

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Vol.14, No. 2 Japanese Journal of Lactic Acid Bacteria

LAB.

The total kimchi production was estimated to

be 1,500,000 M/T in 2000 and one fourth of the

kimchi consumed was commercially produced. Ac-

cording to a national survey, an adult consumes

50-100g/day of kimchi in summer and 150-

200g/day in winter!)

During the past 50 years, many species of bacte-

ria, yeasts, and fungi have been isolated and re-

ported from kimchi samples. The major micro-organisms responsible for kimchi fermentation are

LAB and yeasts which are known to be responsi-

ble for the softening of kimchi texture and the

off flavor. The major species of LAB isolated and

identified from kimchi are Leuconostocmesente-

roides, Leuconostoc dextranicum, Leuconostoc cit-

reurn, Lactobacillus brevis, Lactobacillus fermen-

turn, Lactobacillus plantarum, Pediococcus pen to-

saceus, and Streptococcus faeculis.'

The sugars present in the raw materials are con-

verted to lactic acid, acetic acid, carbon dioxide

and ethanol by hetero fermentative LAB during

kimchi ripening, and these acids and carbon diox-

ide are responsible for the fresh and carbonated

taste of kimchi. However, after a certain period of

time excessive lactic acids are formed and undesir-

able flavors develop due to the growth of homo

fermentative LAB and yeasts.1.2)

In the kimchi fermentation system, the hetero

fermentative LAB producing organic acids and car-

bon dioxide from sugars are major species in the

early stage of fermentation, and homo fermen-

tative LAB producing excessive lactic acid are

major species in the late stage of fermentation. It

has also been shown that low salt concentration

and low temperature (eg, 2% and 10 °C ) favor

growth of hetero fermentative LAB, while high salt concentration and high temperature (eg, 3.5%

and 30 °C ) favor growth of homo fermentative

LAB. Therefore, salt concentration and tempera-

ture are the key factors for controlling kimchi fer-

mentation!'

Besides the above mentioned key factors for con-

trolling kimchi fermentation, many other factors

such as the raw materials, processing methods,

and natural preservatives and starters which af-

fect kimchi fermentation and preservation have

been reported in reviews and books."

In general the factors that affect kimchi fermen-

tation are microorganisms, temperature, salt con-

centration, fermentable carbohydrates, other nut-

rients, any inhibitory compounds present in the

raw materials, oxygen and pH. In this review,

the salts and salting conditions, temperature, raw

materials, natural preservatives and selected start-

er cultures related to kimchi fermentation will be

discussed in detail.

II. Factors affect on kimchi fermentation

1. Salts and salting conditions

The concentration of salt is one of the key fac-

tors for controlling kimchi fermentation and pres-

ervation at various temperatures. There are more

than 200 kinds of kimchi available in Korea. How-

ever, the salt concentrations of these kimchi all dif-

fer depending on the maker. A flow-chart for

processing baechu-kimchi is shown in Fig.1. Prior to kimchi preparation the major raw mate-

rials such as Chinese cabbages and radishes may

be salted with either a salt solution (brine meth-

od) or dry salt (direct addition method) and wash-

ed with clean water. This treatment is the most

important step for fermentation and maintenance

of kimchi quality. It has been reported that the op-

timum salt concentration for kimchi is about 2.0-

3.0%, while appropriate level is determined by

individual experience.2) Therefore, it is necessary

to optimize the salting condition. Of the two salt-

ing methods, the direct addition method is most

widely used at the household level, but has the dis-

advantage of being difficult to control the final

salt content of the kimchi. The brine method is

preferable for commercial production of kimchi. A

satisfactory quality for kimchi can be obtained

when the cabbage is salted for 3-6 hours using 15

to 20% salt solution.'

Salting is carried out over a range of time

from 3 to 15 hours depending on the salt concen-

tration, temperature, variety, cutting method and

size of the cabbage. For baechu-kimchi, the final

salt concentration is adjusted to 2.0-3.0% of the

overall ingredients, this concentration being best

for optimum fermentation. This concentration is

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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 —


maintained during fermentation and preservation. If the salt concentration is below the optimum con-centration, fermentation proceeds too quickly and can cause excessive acidification and softening.

On the other hand, color and flavor are not accept-able when the salt concentration is over 5%.2) De-pending on the salting time, free sugars and amino acids are reduced in raw cabbage and the texture, chemical and physical properties, and total microbial counts change during saltine')

Generally, salting reduces the moisture content (10-12%), relative volume, and weight, as well as the internal void space of the cabbage. These changes affect the physical properties of the vege-table, especially the flexibility and firmness of the tissue, which gives a distinctive textural property to the final product. As a result of brining, the total amount of microorganisms, such as aerobic counts, in salted cabbage are reduced (11-87%), and LAB increase (3-4 times). The amount of reducing sugars also decreases. (7-17%)7,11)

Washing conditions for salted cabbage is also im-portant for quality preservation of the kimchi.'2) Chinese cabbage treated with a 1000 ppm solution of grapefruit see extract or citric acid at 10°C shows a retarded increase in titratable acidity and a decrease in pH and reducing sugar concentra-tion.". Kimchi made from Chinese cabbage soaked in a heated 10% salt solution at 40°C has im-proved quality and shelf-life.'

Fig.2 shows the effect of salt concentration and temperature on acid production during kimchi fermentation.H) Total acid was more at lower salt con-centration (2.25%) than at any temperature tested for high concentration. At the lower salt concen-tration, maximum acidity was reached in a shorter period of time. At 30°C and 2.25-3.5% salt concentration, the acidity of kimchi was main-tained in the same pattern throughout. An acidity of 1.55% was reached in 5 days and was main-tained at 1.6% thereafter, but at 5.0 and 7.0% salt concentration, the acidity reached 1.4 and

1.1% after 5 and 6 days, respectively. The effect of salt concentration on dongchimi

(ponytail Chinese radish kimchi) fermentation was also studied's). Diced Chinese radishes were fer-mented at 4°C with a salt concentration of 1.5-

6.3%. The pH level reduced during the fermenta-

tion, while the total acid content of dongchimi in-

creased and the salt concentration of the

dongchimi liquid decreased. Equilibrium for the

salt concentration between the dongchimi liquid

and the solid radish was achieved after 15-22 days

of fermentation. Vitamin C and the reducing

sugar content of the dongchimi liquid and Chinese

radish increased until 15-22 days of fermentation,

and then decreased. Salt concentration had a sig-

nificant effect on the sensory properties of

dongchimith)

Recently, to examine the quality of mu]-kimchi,

the temperature (4, 15, and 25°C for 10 days) and

salt concentration (0, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, and

3.0%) in water was conducted, and it was found

that the pH was the lowest and the acidity the

highest in the in u/-kimchi containing 1.0% salt.

The total vitamin C content in mui-kimchi contain-

ing 3.0% salt was higher than in the low-salt sam-

ples after the optimum ripening time and the

overall palatability of mui-kimchi showed the high-

est score in the 1.0% salt sample.16)

2. Temperature

After salt concentration, the most important fac-

tor affecting kimchi fermentation is temperature,

since the kimchi fermentation occurs mainly by

the microorganisms naturally present in the raw

materials. Kimchi is now available year-round but

the quality of .kimchi differs depending on geo-

graphical location and season. Ambient tempera-ture is used for making kimchi for personal con-

sumption. Kimchi fermentation and over acidifica-

tion occurs simultaneously at ambient tempera-

ture.

Fig.3 shows the changes of pH and total acids

during kimchi fermentation at various tempera-

tures. Ripening time of kimchi depends on the fer-

mentation temperature, therefore differences in pH

and acidity were seen. At 20°C , the pH dropped

sharply with increasing acidity, but pH and acid-

ity at 10°C changed more slowly than at higher

temperatures.

Maximum total acid produced in kimchi at 20°C

and 15°C is 1.6%, but never exceeds 1.2% at 10°C.

A panel evaluation determined that the pH and

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acidity of the optimum ripening period for kimchi

were 4.2-4.5 and 0.6-0.8% (as lactic acid), respec-

tively.')

The optimum ripening time and the edible pe-

riod for kimchi varied depending upon the fermen-

tation temperature and salt concentration as

shown in Table 1. At 30°C, the optimum ripening

period was 1 day and the edible period was 1-2

days. At lower temperatures, the optimum ripen-

ing time and the edible period were longer than

at higher temperatures. At 5°C and above 5.0%

salt concentration, kimchi ripened very slowly and

at 7.0% salt concentration it did not ripen even

after 180 days fermentation. 14)

Chemical changes, LAB and yeast counts in

kimchi prepared by commercial manufacturers in

large scale were monitored at different fermenta-

tion temperatures. It was confirmed that the opti-

mum pH of kimchi is around 4.2 which was

reached within 2 days at 25 °C , 3 days at 15 °C ,

and 23 days at 5°C fermentation, respectively. 17)

Differences in the quality characteristics such as

pH, acidity, reducing sugar content, microbial

counts and sensory properties between whole Chi-

nese cabbage kimchi (pogi -kimchi) and sliced Chi-

nese cabbage kimchi (ma t-kimchi) were examined

during fermentation at 20°C for 10 days and 5°C

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

— 60 —


tation, approximately 2 days at 20°C and 10 days

at 5 °C , than mat-kimchi. Odor, color and flavor

scores for the kimchi were higher in the samples

fermented at 20 °C than those fermented at 5 °C ,

also there were no great differences in the sen-

sory properties of pogi-and mat-kimchi. The gas

composition of the packages containing the kimchi

fermented at 20°C showed increased CO2 concentra-

tion and decreased 02 concentration after 3 days

for both kimchi varieties.'

The effect of fermentation temperature on the

sensory, physicochemical and microbiological prop-

erties of kakdugi (cubed radish kimchi) and on

the free sugar, organic acid and volatile com-

pound levels in kakdugi during fermentation were

also investigated. '9.2°) After initial fermentation for

12, 24 and 36 hr at 20°C, kakdugi was fermented

for 57 days at either 4 °C , 10°C or 20 °C , respec-

tively. The pH was decreased to between 4.1 and

4.3 from the initial pH 5.8, and the total acidity in-

creased 2-4 times that of the initial value (0.2%).

The number of LAB remarkably increased in palat-

able period and gradually decreased thereafter."'

Free sugar levels decreased at each temperature

during fermentation (with the - exception of man-

nitol, levels of which increased) although decreases

were less marked in samples fermented at 4t Of

the organic acids tested, lactic acid production

was the most pronounced, increasing substantially

with time and temperature. In contrast, malic

acid, which was the most abundant organic acid.

initially, decreased in concentration during fermen-

tation, and this decrease was most pronounced at

higher temperatures.

Levels of the volatile compound, methyl ally' sul-

fide, were initially very low, but increased dramati-

cally up to approximately 45 days after which

levels decreased. The increase corresponded to in-

creased aroma in the sensory evaluations. These re-

sults suggest that fermentation at 4°C , following

an initial fermentation at 20°C for 36 hr, is suit-

able for the production of good quality kakdugi

with high free sugar and organic acid contents.20)

In order to investigate the fermentation charac-

teristics of kimchi, which was made at 12°C and

fermented at 17°C and 4°C, the pH, total acid con-

centration, total cell counts of microorganisms,

LAB, dissolved carbon dioxide content, reducing

sugar content and temperature at the center of

kimchi jars were measured . The pH and the

total acid content of kimchi that was fermented

at 17°C for 4 days were almost the same as those

of kimchi fermented at 4°C for 48 days. The total

cell counts of microorganisms and LAB in kimchi

which were fermented at 17°C for 2 days and 4°C

for 9 days were 1.5 X 109 and 6.3 X 108 cells/m/, and

2.0 x 108 and 8.7X 107 cells/m/, respectively. The re-

sults showed that it took 23 and 35 hr, respec-

tively, to reach the temperature of 17°C and 4°C

at the centers of a jars during bulk fermentation

of kimchi from an initial temperature of 12°C. 21)

The characteristics of natural lactic acid fermen-

tation using radish juice were investigated at dif-

ferent salt concentrations (0-2%) and temperatures

(10-30°C) using low salt kimchi (a kind of water

kimchi). It was found that the LAB isolated from

radish juice fermented at 2% salt concentration

was mainly Leu. mesen teroides, Lac. plan tarum

and Lac. brevis. Growth rate of LAB increased

with increasing temperature at 1% salt concentra-

tion and the LAB was still active at 10 °C . The

time required to reach pH 4.0 during fermentation

with juice containing 1% salt was 11-13 days at

10°C and 2-3 days at 30°C .22'

The effects of fermentation temperature (0-15°C)

and salt concentration (1.5, 2.75, 4.0%) on the fer-

mentation parameters of kimchi were also ana-

lyzed by response surface methodology. The pH

decreased and acidity increased with increasing fer-

mentation time; while reductions and incremental

rates increased as temperature increased and salt

concentration decreased. The optimum pH of 4.2

was achieved within 14-24 days at 5-15°C , but at

5°C , the pH was still >4.2 after 24 days. Maxi-

mum edible acidity (0.75%) was reached within 8

days at 15°C , but at 0°C , acidity was only 0.35-

0.43% after 24 days of fermentation. Edible peri-

ods for kimchi, based on the acidity range 0.4-

0.75%, were 4, 10, and 18 days for the fermenta-

tion at -15, 10, and 5°C , respectively, at 2.75% salt

concentration.")

3. Raw materials

Kimchi, a fermented vegetable food with various

— 61 --


components (including seasoning and spices), has

been the most popular side dish served with cooked rice for hundreds of years in Korea. In

total, there are about 200 kinds of kimchi, whose

raw materials are mainly Chinese cabbage and rad-ishes. Dried red pepper powder, garlic, green

onion and ginger are the widely used seasonings. The types and amounts of seasonings used in

kimchi vary greatly between manufacturers and

processors. The quality and species of the major in-gredients significantly affects fermentation and the product characteristics of kimchi.

The important raw materials of kimchi are di-

vided into three groups: the major raw materials,

sub-ingredients (spices) or fermented fishery prod-ucts, and optional (minor) ingredients.

As seen in Table 2, Chinese cabbage is the most common major raw material for preparing kimchi

while radishes are used for kakdugi (cubed radish

kimchi) and dongchimi (whole radish kimchi with water) preparation. Cabbage, whole radish, cucum-

ber, mustard leaves, green onion, and leeks which are available in different seasons and localities are

the raw materials used for making special kimchi

in Korea. One of the important criteria for making the

good taste of kimchi is the selection of good qual-ity raw materials, followed by formulation of

kimchi ingredients and seasonings.

Table 3 shows the basic ingredients for making baechu-kimchi, kakdugi, dongchimi, and m ul-

kimchi, but the most simple kimchi recipe includes

salted cabbage 100 g, hot pepper powder 2 g, gar-lic 1.5g, green onion 2 g, ginger 0.5 g and final

salt concentration of 2-3%.14) Generally softer texture and higher sugar con-

tent vegetables are desirable for making good qual-

ity and good tasting kimchi. However, hard texture vegetables are more favorable for long-

term preservation without softening!' Among the many kinds of kimchi, baechu-kimchi

has been consumed for the longest time as a tradi

tional fermented vegetable food in Korea. The kind and amount of ingredients involved in

baechu-kimchi preparation affect the kimchi fer-mentation rate. Effects of raw materials and ingre-

dients on kimchi fermentation have been

extensively studied."-")

Besides the temperature and salt concentration,

the type of kimchi is also a factor in controlling

kimchi fermentation. Therefore, the three main

types of Chinese cabbage kimchi, baechu-kimchi

and tongbaechu-kimchi (semi solid types of the cab-

bage kimchi prepared with a large amount of hot

pepper powder and a small amount of water) and baek-kimchi (a liquid type of kimchi prepared

with a small amount of hot pepper powder and a

large amount of water), were selected as models

to compare the fermentation characteristics of

kimchi. The amount of hot pepper powder and

water are believed to be the primary (or external)

and secondary (or internal) factors, respectively, af-

fecting kimchi fermentation.')

The growth of microorganisms can be controlled

by the appropriate addition of raw materials.

Among the sub-ingredients, hot pepper powder,29-32)

radishes,34) fermented anchovy and shrimp,'")

starches,35.3" reducing sugar,"A soluble solids,' and

protein sources')have been probed for their ability to promote kimchi fermentation, but garlic,

leaf mustard and leek have been shown a have de-

laying effects,"."-") while green onion and ginger

have controversial. effects on kimchi fermenta-

tion."-')

Garlic is used most frequently as a sub-

ingredient (100%) in kimchi. Since ground garlic

is used in kimchi making, alliin is changed to

allicin which has an intensive taste. Allicin takes

part in fermentation of kimchi by inhibiting the

growth of various unnecessary microorganisms de-rived from sub-ingredients during the initial fer-

mentation period and slows the fermentation of

kimchi. Garlic improves the storage capacity by

prolonging the LAB fermentation period and re-

sults in less a.cidification.29,30,2.43A6) With fermenta-

tion of kimchi, the intensive hot taste of garlic

slowly changs to a harmonized taste and flavor.31)

The composition of pigments in hot pepper con-

sists of 40 different carotenoids, with capsanthin

and capsorubin being the most widely found, and

carotenes such as provitamin A. The average

amount of hot pepper added to kimchi was found

to be 2.24% with a frequency of use of 97.3%. In

spite of the fact that hot pepper was reported to

— 62 —


Table2. Raw materials used for kimchi preparation

Table3. Ingredient composition of various kimchi varities

— 63 —


promote the fermentation of kimchi, it did not show any significant increase in sour taste and

did not affect sweetness, saltiness, palatability or

crispiness."

Green onion and leek contain various allyl sul-

fides, carotenes and vitamin C. The frequency of

use in common cabbage kimchi was 72.8% for

green onion and 32.4% for leek, which both are

much lower than the 100% for garlic and 97.3%

for hot pepper. The amounts of green onion and

leek used for kimchi making are still high, ie, 0.6-

0.9% for green onion and 2.0-6.0% for leek. Re-

cently, it has been reported that leek retards the

fermentation of kimchi due of its antimicrobial ac-

tivity.")

Ginger contains unique components like citral

and linalool, and hot spicy components such as

gingerone and shogaol. Ginger causes a delay in

fermentation and there were no significant differ-

ences in the sourness, sweetness, saltiness, spici-

ness, palatability, unpleasant and overall tastes,

acidic odor and color between the kimchi fer-

mented with and without ginger.'"

Fermented anchovy and shrimp contain large

amounts of proteins and amino acids, and have

their own unique taste and flavor. Therefore,

these sub-ingredients affect not only the nutri-

tional balance but also the sensory quality of

kimchi. These fermented fish products and other

protein sources such as skim milk, soy protein iso-late, beef extract, and fish protein produced high

lactic acid concentrations and promoted the

growth of LAB."."'")

The frequency of addition of starch and sugar

in kimchi making was 27% with a concentration.

of 0.4-3.0%, and sugar was used for sweet and har-

monized tastes. However, since starch and sugar

are utilized as carbon sources by various microor-

ganisms present in kimchi, they affect kimchi fer-

mentation and sensory quality. In the results,

starch and sugar promote the fermentation of

kimchi and contribute greatly to the harmony of

tastes by reducing the hot and overall tastes, as

well as the acidic and garlic odors." It was also

found that both wheat flour and glutinous rice

flour hastened the fermentation of yulmoo-

kimchi.")

4. Natural preservatives

The groups of LAB involved in kimchi fermenta-

tion continuously produce organic acids after the

optimum ripening, and cause changes in the com-

position of kimchi. These changes are called over ripening or over acidification, and are often ob-

served in summer kimchi and winter kimchi

stored for extended periods of time. Over ripening

is the most serious problem for storage of

kimchi. Since over acidification is mainly due to

the activities of lactic acid-producing LAB, the

best way to overcome this is to control the

growth of LAB without destroying the quality of

the kimchi.

Screening of natural preservatives such as me-

dicinal plants, edible plants, herbs and spices,

antimicrobial agents and related compounds to in-

hibit kimchi fermentation have been studied exten-

sively.° Among 42 oriental medicinal plants test-

ed, Baical skullcap barks (Scutellaria baicalensis),

and powders of Assam indigo (Baphicacanthus

cusia) were very effective for preserving kimchi.

Among 32 herbs and spices tested, peppermint

leaves (Mentha piperita L.), cinnamon barks

(Cinnamomum verum Presl), lemon balm leaves

(Melissa officinalis L.), flower buds of clove (Euge-nia caryophyllate Thunb.), hop leaves (Humulus

lupulus L.), rosemary leaves (Rosmarinus offici-

nails L.), sage leaves (Salivia officinalis L.), horse

radish roots (Moringa oleifera Lam.), and the

leaves and flowers of thyme (Thymus vulgaris L.)

showed high antimicrobial activity against micro-

organisms in kimchi. Clove was the most effective

microbial inhibitor, when added to fresh kimchi.

However, sensory testing was not appropriate for

evaluation of the effect of herbs and spices, since

their highly specific flavors affect the taste of

kimchi. Among 28 fruits, vegetables and related

plants tested, the leaves of pine tree (Pin us rigida), persimmon (Diospyros kaki) and oak (Quer-

cus glauca) also demonstrated significant bacteri-

cidal effects. In addition, of 21 natural preser-

vatives added individually to fresh kimchi, only

nisin and caffeic acid were able to inhibit fermenta-

tion.°

The changes of pH and acidity of baechu

kimchi and mu] kimchi were remarkably inhibited

— 64 —


by the addition the tea catechins to a level of

2mg/g fresh baechu, the results suggesting that

the tea catechins can be successfully used for ex-

tending the shelf-life of kimchi.48)

Studies were carried out to investigate the ef-

fects of Lithosperrnurn erythrorhizon and Gly-

cyrrbiza uralensis (LG), both with and without

dipping salted Chinese cabbage in 1% chitosan so-

lution (LGDC), on the fermentation of kimchi at

10 °C for 25 days, The sour taste of LG and

LGDC treated kimchi changed more slowly than

that of the control during fermentation. The shelf

life of LGDC treated kimchi was extended by

more than 10 days compared with the control."

By the addition of 1% mixed extract of Lithos-

permurn erythrorhizon and Scutellaria baicalensis

and 1% crab shell treated with ozone to kimchi,

color, flavor, and sourness were negatively ef-

fected to a slight degree, while texture and over-

all acceptability were found to be the same or

slightly improved compared with untreated

kimchi.') It was also found that the kimchi con-

taining. 2% ozone treated crab shell powders

showed both strong neutralization action for 0-25

days and buffer action after 25 days during fer-

mentation at WC.")

Addition of 500 ppm grape fruit seed extract

(GFSE)) showed the highest pH during fermenta-

tion at 20°C and the lowest titratible acidity corn-

pared with the control. The total microbial counts were higher than the LAB counts immediately fol-

lowing the preparation of kimchi, but they were

similar after three days. However, sensory evalua-

tion of 3 day old kimchi samples showed a signifi-

cant difference (P<0.05) between the control and

the treated kimchi (100, 300 and 500ppm) when

evaluating odor, color and taste. Only the 50 ppm

GFSE sample was found not to be significantly dif-

ferent from the contro1.52)

Recently, the fermentation characteristics of

mustard leaf kimchi with added green tea and

pumpkin powder have been studied and it was found that the sensory scores for flavor, aroma

and overall acceptability were highest in the

kimchi with 0.3% pumpkin powder and 0.2%

green tea powder.")

The effect of chitosan (0.5%) on the properties

of kimchi was studied during fermentation at

20 °C for 8 days. It was found that chitosan re-

duced the total number of microorganisms and lev-

els of Leuconostoc species and Lac. plantarum in

kimchi, and the lower molecular weight chitosan

fraction had the greatest effect on the levels of

Leuconostoc species. Also, chitosan reduced the in-

tensity of sour and stale flavor in kimchi, and

the content of reducing sugar in control kimchi

was lower than in the chitosan containing kimchi

for the first 6 days of fermentation at 20 °C.

Malic acid content was lower and lactic and acetic

acid content were higher for the control kimchi

than for the chitosan containing kimchi for the

first 4 days of fermentation. Control kimchi con-

tained more succinic acid than the chitosan con-

taining kimchi for the first 2 days of

fermentation!' Leuconostoc species and Lac,

plantarum were higher in the control than in the

chitosan containing kimchi dissolved in 0.3% ace-

tic acid and 0.05% sodium benzoate.') It was also

found that addition of chitosan to kimchi influ-

ences pectic substance levels and improves their

textural properties.')

Two percent ginseng in kimchi had the best over-

all preservability and quality, and promoted the

growth of Lac. plantarum and Lac. ferment=

and inhibited the growth of Leu. mesenteroides

and Ped. cerevisiae.")

Addition of sap from pine needles (Pin us

densiflora) delayed kimchi fermentation by slow-

ing down the decrease in pH and inhibiting the

growth of Lactobacillus species!') Water extract of pine needles had stronger in-

hibitory effects against Lac. plantarum than again-

st Leu. rnesenteroides.")

It was found that mustard oil had antimicrobial

effects on the major LAB of kimchi such as Lac.

plan tarum, Lac. brevis, Leu. mesen teroides and

Ped. cerevisiae, and mustard powder (0.1%) and

mustard oil (200 ppm) extended the shelf-life of

kimchi, after 15 days storage at 15t.60)

The extract of bamboo leaves had a wide range

of antimicrobial activity against Brettanomyces

custersii, Klebsiella oxytoca, Pichia membranae-

faciens which cause kimchi softening5 Recently,

the effects of cuttlefish bone (Sepiae os),') enoki

— 65 —


mushroom (Flammulina velutipes),' Monascus

koji," and boiled-dried edible seaweed (Hizikia fusi-

forme)65 on the fermentation and quality of

kimchi have been studied.

5. Starters

The quality of kimchi can controlled by desir-

able microorganisms, and various fermentation

conditions such as temperature, salt concentration,

and nutrients in raw materials. As already men-

tioned, kimchi fermentation and ripening are car-

ried out by the microorganisms present in the

raw materials. Sugars in raw materials are con-

verted to lactic and acetic acid, carbon dioxide,

ethanol and mannitol by the LAB growing at 1-

3% salt concentration. The total count of kimchi

microorganisms reaches its maximum level (1 X 10"

cells/m4 at optimum ripening time, after which

the number of LAB decreases slowly and main-

tains what is called the 2nd maximum level (1 X 10' •

cells/nil).

A hetero fermentative type of LAB, Leuconostoc

mesenteroides, is a major bacterial component of

kimchi from the initial to the middle stage of fer-

mentation. During these stages, hetero fermenta-

tive type LAB produce various metabolites such

as lactic acid, acetic acid, ethanol, carbon dioxide,

mannitol, and dextran which are associated with

the taste of kimchi, and the number of LAB

reaches its maximum during the optimum ripen-

ing period. However, total number of Leu.

mesenteroides decreases sharply when the pH of

kimchi is decreased to 4.0. On the other hand, a

homo fermentative type LAB, Lac. plan tarum,

which has a strong pH tolerance under high or-

ganic acid concentrations, continuously increases

in count during kimchi fermentation to the last

stage. It has been reported that the acidification

of kimchi is mainly caused by Lac. plantarum.")

As seen in Table 4, Lac. plantarum, Lac. brevis,

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

— 66 —


Lac. bavaricus, Lac. ho.mohiochli, Ped. cerevisiae,

Leu. mesenteroides, Leu. dextranicum, Lea.

paramesen teoides, and Sac.fermen tati were isolated from kimchi and have been used as kimchi start-

ers to improve the quality and shelf-life of

kimchi 66-71)

The combination of Leu. mesenteroides, Lac.

brevis, Lac. plan tarum and Ped. cerevisiae, all

strains isolated from kimchi, have been used as

starters for kimchi fermentation. These starters in-

crease the fermentation rate, and mixed strains

are more effective than single strains in produc-

ing better organoleptic quality kimchi."

Generally, kimchi fermentation has been carried

out at relatively at low temperatures, and psy-

chrotrophic LAB have been isolated and character-

ized from kimchi fermented at 5°C . 24,67) Therefore,

psychrotrophic LAB isolated from kimchi.fermented at low temperature were studied as start-

ers for their effect on kimchi fermentation. The

results indicate that the fermentation period can

be shortened by use of LAB starters isolated

from low temperature kimchi. Among the LAB

used as kimchi starters, it was shown that

Leuconostoc species were more effective than any

other Lactobacillus species tested for kimchi fer-

mentation."

Because the acid production from the hetero

fermentative type LAB is lower than that of the

homo fermentative type LAB, the addition of an

acid tolerant mutant strain Leu. mesenteroides as

a starter for kimchi fermentation may inhibit the

rapid pH decease and lactic acid production during

kimchi fermentation. Therefore, the mutant strain

Leu. mesenteroides M-10, which could grow at low

pH (3.0) at 10°C and produced more CO2 than the wild type, was found to be a superior kimchi

starter. With respect to total acceptability, the

kimchi prepared using the mutant strain M-10

was better than the other strains, and use of the

mutant strain extended the optimum ripening pe-

riod of kimchi by two fold compared with that of

the control. These results show that a mutant

strain of Leu. mesenteroides which is more stable

to growth in acidic conditions was able to extend

the edible period of kimchi."

Psychrotrophic yeast, Saccharomyces fermentati

YK-19, that showed better growth at 10°C than at

25°C in the medium containing 0.3% lactic acid

and 0.6% acetic acid, was isolated from kimchi

and used as a kimchi starter in order to prevent

over acidification of kimchi.') The addition of Sac.

fermentati YK-19 prolonged the period of opti-

mum fermentation (at pH 4.2 and 0.6-0.8 acidity)

by >63%. The lactic acid content increased rapidly

in control samples, followed by the kimchi with

Sacharomyces sp. YK-17 and Sac.fermentati YK-19

as starters. The growth of Lactobacillus species

was inhibited by the addition of yeast starter, par-

ticularly by Sac. fermentati YK-19. Furthermore,

sensory evaluation scores for acidic and moldy fla-

vor were reduced by starter addition, while scores

for freshness increased.'"

Lou. paramesen teroides P-100, a psychrotrophic

mutant which grew well at pH 4.0, and 10°C, and

in an organic mixture (lactic acid:acetic acid;1:2)

was derived from the wild type Leu.

paramesenteroides Pw. Kimchi with added mu-

tant strain P-100 had better taste than that of con-

trol kimchi by the sensory evaluation test and the

optimal pH range of kimchi extended up to about

2.2-2.5 times. In the kimchi added with Leu.

pararnesenteroides P-100 , the succinic acid content

was higher than for that of the others tested,

and the total number of Lac. plantarum was re-

duced about 2.5 fold when compared to the con-

trol kimchi.")

Leu. mesenteroides M-100, an acid tolerant mu-

tant derived from the wild type strain Leu.

mesenteroides Mw, and Sac. fermentati YK-19, an

acid utilizing and aromatic flavor producing yeast,

were tested for their ability to retard acidification

and prolong of the edible period of kimchi."'") The

addition of Lea. mesenteroides M-100 to kimchi

preparation may induce the prolonged acidification of kimchi because of its low production of lactic

acid and increased growth in comparison with

Lac. plantarum. Also Sac. fermentati YK-19 may

lengthen the edible period of kimchi by reducing

the content of lactic acid and acetic acid during

the later period of kimchi fermentation, and the

superior flavor in the kimchi group treated with

starters may be due to the various substances, car-

bon dioxide, and succinic acid produced by Leu.

— 67 —


mesenteraides M-100 and Sac. ferrnentati YK-19.74) The inoculation with mutant strains of Leu.

mesen teroides and Leu. paramesen teroides in-

creased adipic acid resistance compared with the

wild type species and its effect on the shelf-life of kimchi were evaluated. The combination of both

mutants was more effective than that of any sin-

gle strain in extending shelf life of kimchi. The op-timum inoculation was 0.005% of a 1:10 mixture

of Leu. mesen teroides: Leu. paramesenteraides ac-

cording to the results from acidification tests and sensory analysis.')

III. Conclusion

Kimchi has a unique taste characteristics having sour, sweet and carbonated tastes with medium

texture. In this respect kimchi differs greatly from sauerkraut that is popular in the West. The

optimum acidity, pH and salt concentration of

kimchi are 0.6-0.8% (as lactic acid), 4.2- 4.5 and 2.0- 3.0%, respectively. Kimchi 4rmented at lower tem-

peratures are superior in quality and taste to those fermented at higher temperatures.

Kimchi fermentation is complex and is due

mainly to certain LAB and yeasts naturally pre-sent in the raw materials. Several physicochemical

and biological factors such as salt and sugar con-

centration, temperature, raw materials, natural

preservatives and starter culture influence the qual-ity of kimchi. Among the many factors affecting

kimchi fermentation, salt content and temperature

are the most important, followed by the quality of raw materials and microorganisms, typically

hetero fermentative LAB and psychrotrophic

yeasts. The salting of the major raw materials of

kimchi is a very important step for fermentation

and for the quality of the kimchi. The optimum salt concentration of kimchi is around 2.0-3.0%.

Under the optimum salt concentration, tempera-ture is the next important factor for controlling

kimchi fermentation and preservation, The

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sugars and protein sources are also important for

making quality and good tasting kimchi.

Many homo and hetero fermentative LAB, such

as genus Lactobacillus, Leuconostoc, Weissella,

Lactococcus, Streptococcus and Pediococcus were

isolated and identified from various kimchi sam-

ples, but genus Leuconostoc, Weissella and other

LAB producing organic acids, carbon dioxide and

bacteriocins are the most important microorgan-

isms for controlled fermentation of kimchi.

Psychrotrophic and acid tolerant LAB, especially

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Finally, further research is needed to develop

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tion using starters and for the long-term preserva-

tion of commercial kimchi at ambient tempera-

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factors affecting kimchi fermentation

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