Principles of Kimchi Production
After
various vegetables are mixed with seasoning to make kimchi,
the fermented kimchi has an unique taste and aroma, quite
different from the taste of the ingredients used. It is known
that the mechanism of kimchi making is a matter of exchange
and discharge of water in the vegetable by osmotic pressure.
In the process of fermentation, microorganisms and enzymes
work on the vegetable and then the fresh vegetable flavor
is changed into an unique aroma. The sophisticated aroma and
flavor of kimchi are produced during the process. During the
process not only for the seasoning but also for the action
microorganisms on the fermentation are equally important.
Among various microorganisms, lactobacillus plays the most
important role in kimchi fermentation. Sometimes low salt
kimchi produces an undesirable mold and enzyme. However, the
lactic acid produced by lactobacillus works on the organic
component of the vegetables to produce flavor and prevent
the growth of unwanted mold.
In the process of kimchi production, preserving the vegetable
with salt is very important. It determines not only the taste
and texture of kimchi but also the storage status of kimchi.
At more than 20 percent the salt concentration reduces the
water content of the vegetables and ceases microorganism activity,
or at least reduces the activity level. At 8-10 percent salt
concentration, decayed bacteria and fungus activity begin
decreasing, whereas at this concentration level lactobacillus
produces lactic acid better than any other microorganism.
However, it is important to prevent the production of film
yeast which consumes the lactic acid.
When the pH of kimchi is lower than 3.0, the activity of microorganisms
ceases. The mechanism can be explained by the action of the
hydrogen ion which coagulates the protein, since no microorganism
can survive without protein as a nutrition source. Acid produced
during fermentation also prevents the browning effect of vegetables
due to the antioxidant effect. The production also stabilizes
the seasonings used and keeps the pigmentation of the vegetables.
Kimchi used to be the major source of vegetables consumed
by Koreans during the winter when no fresh vegetables were
available.
The nutrient contents of kimchi vary according to the ingredients
used and the condition of fermentation. The main ingredients
of kimchi have few in calories, high water content, high fiber
content, and various vitamins. Red chili pepper is a good
source of vitamin A and C for Koreans. Garlic has a sterilization
effect and contains a large amount of allylsulfide. Spring
onions, especially the green part, are a good source of vitamin
A and C, too. The bitter taste of cucumbers contains ellaterin,
and this increases digestion. Potassium in cucumber has a
diuretic function.
Salted and fermented anchovies and shrimp used in kimchi as
ingredients are good sources of protein, amino acids and fats
that are lacking in the vegetables. Calcium in the salt-fermented
anchovies and shrimp play a role as an alkali food and have
a positive effect on the maintaining the homeostasis in blood.
Oysters are the most commonly used seafood as an ingredient
in kimchi and are well known as a good source of calcium,
iron, glycogen and vitamins.
Glutamic acid and glycine in oysters also help to produce
the sophisticated taste of kimchi.
Kimchi is a low-calorie food. It is low in calories and fat
content but is high in fiber, vitamin A, ascorbic acid, calcium,
phosphorus, iron and has a large amount of other minerals.
Lactic acid produced during the fermentation of kimchi is
regarded as having a positive effect on preventing cancer.
Cabbage, garlic, and red chili pepper have a large amounts
of minerals as well as medicinal contents. Large amount of
fiber from kimchi can not be used as nutrients but have a
great effect on the peristalsis of the stomach and the intestines,
thus preventing constipation and cancer of the large intestines.
There is a plenty of scientific evidence that red pepper and
garlic have the effect on lowering the blood cholesterol level,
antithrombosis, as well as an antioxidant effect. Therefore,
kimchi is recognized as a health food with a good nutritional
balance.
Role of Seasoning
Vegetables and various seasonings are the main ingredients
of kimchi, and when they are mixed together, various kinds
of phenomena occur. For instance, when salt is added to green
vegetables, glossy and fresh vegetables become soft and tender.
It is because the fresh vegetable extracts water through the
action of the salt. Not only salt, but also other seasonings
used in kimchi production have the same effect of permeability
to extract water from vegetables. By the action of permeability,
the chemical components of the seasonings go into the vegetables
while water in the vegetables comes out.
Vegetables contain billions of cells, and each cell is covered
by a cell membrane with water and various components stored
inside. Therefore, even if vegetables are torn apart, the
basic cell structure of a vegetable is maintained for a while.
Of course, since metabolism is not taking place, these cells
are destroyed and dead sooner or later, destroyed by their
enzymes or microorganisms in the air, but until then their
activity continues. When these cells are forcibly destroyed
by the permeability of seasonings before microorganisms can
infiltrate, the vegetables lose freshness and the exchange
of chemical components takes place in the cell.
It is extremely important for kimchi not to lose the freshness
of its vegetables and to pro-duce a savory chewable taste.
Even if there is a certain taste, if the sensitivity of the
tissue turns bad, the taste of the kimchi is reduced. Therefore,
if we want kimchi with a fresh vegetable texture, it should
be prepared before the pectin flows out of the vegetables.
Pectin is dissolved by an enzyme called pectinase and largely
classified into pectinesterase and polygalacturonase. It exists
within vegetable cells, and when cell membranes are destroyed
under whatever conditions, it comes out and dissolves pectin.
Therefore, kimchi should be prepared before pectin is dissolved,
so fresh and not too mature vegetables should be chosen to
make good kimchi. There are two ways to prevent the dissolving
of pectin without destroying cell membranes. The first way
is the dehydration method, and the second way is the method
of curbing the action of pectin-dissolving enzymes. It is
said that refined salt purchased at stores does not preserve
vegetables well, so they do not become soft inside and crisp
outside. That is because there is little brine in the refined
salt. That is why bay salt is more commonly used since it
has more impurities than refined salt, and these impurities
contain calcium sulfate, which preserves vegetables in a condition
with a soft inside and crisp outside.
The
role of salt in salted vegetables began when mankind discovered salt and used
it to preserve vegetables. The salting process is essential for producing kimchi.
It works on the taste and quality of kimchi, as well as the storage of kimchi
through preventive action against putrefaction.
When vegetables are soaked with salt, salt penetrates the vegetables by osmosis,
while dehydration occurs at the same time, and water is discharged from the
vegetables. Salt on inside and outside of vegetables is dissolved by the discharged
water and osmosis heightens its permeability and turns the salted vegetables
into kimchi. Microorganisms in vegetables cease their activity through the osmotic
action of salt and are destroyed through dehydration or lose their enzymatic
ability. Although halophilie bacteria and enzymes are active in salt water,
in general, most microorganisms stop activity in a less than 10 percent salt
concentration and die. Lactic acid and film yeast can only be suppressed at
15 and 20 % concentrations respectively. When there is plenty of acid, things
work out fine even if there is little salt. In other words, a tasty kimchi can
be produced by utilizing the chain action of salt.
Role of Microorganisms
During the process of fermentation in the production of kimchi, the actions
of microorganisms play an important role as seasoning. Kimchi preserved with
little low salt easily produces mold and yeast while fermenting, due to the
action of microorganisms. Growing mold affects kimchi very badly, because it
leads to decomposition.
When kimchi is mixed with vegetables and seasoning, the water is discharged
by the osmotic pressure of the seasoning. Then the microorganisms in the vegetables
go into action as long as the concentration of the seasoning is not too high.
Among those microorganisms, particularly energetic germs exist not only in the
air, soil and water, but also in vegetables. These germs dissolve protein and
starch, in particular protein into ptomain. And each of these actions - harmful
and harmless or useful and useless - carries on the process of fermentation
or decay. During kimchi fermentation, there is a large amount of lactic acid
production by the action of lactobacillus. As a result, lactic acid accelerates
the maturation of kimchi and produces the flavor. Lactic acid also combines
organically with enzymes and a vegetable component to make a savory taste on
the one hand, and to restrain growth of putrefactive bacteria or harmful fermentation
on the other.
When mixing vegetables with salt, in an 8 to 10 percent salt concentration,
the action of putrefactive bacteria and some other germs are suppressed. However,
as lactic acid has a strong breeding power, the volume of lactic acid increases
and thus putrefactive bacteria is more and more suppressed. But, film yeast,
which is a noxious germ, grows fast at that salt concentration, and, as it is
aerobic, it grows profusely on the surface of liquids in contact with air. At
the same time, since it consumes lactic acid, the amount of lactic acid in the
fluid declines while the putrefactive bacterias activities become more active,
thus incurring great damage to the kimchi. Therefore, it is very important to
prevent the growth of the film yeast for the sake of the useful activity of
lactic acid.
Role of Acids
Acid, together with table salt, acts on kimchi production. When the pH is low,
the growth of microorganisms weakens and below 3.0 pH most of the microorganisms
stop activity. Of course, such microorganisms as film yeast and certain molds
continue breeding below that level, but germs generally are unable to grow under
4.0 pH, but some yeasts can grow below 2.5 pH and molds are very strong against
acid and are capable of breeding at 1.5 pH. However, microorganism's heat-resisting
nature is lowered under acidity. Since acid increases the preservation effect,
there is an effect even if the real pH value is not so low, through the combined
use of preservation and the use of salt. Microorganisms cannot survive due to
coagulating the cellular albumin action. Acid acts not only for preservation
from decay, but also for flavoring and various other phenomena. For example,
if vinegar is added to salted vegetables, it can prevent a browning reaction,
as it has the effect of an antioxidant by deoxidizing unnecessary minerals in
water. Some acids even prevent color change by altering the structure of pigment
which triggers the color change in vegetables.
The
speed of maturation of kimchi can be varied by the ingredients used. At the
same time, the nutritional value varies according to the supplemental ingredients
used and the stages of fermentation. Among kimchi's subsidiary ingredients,
green onions, garlic and red pepper powder prominently heighten the amounts
of lactic acid, succinic acid, acetic acid, and carbon dioxide. It has been
observed that not only does the amount of such organic acid affect taste, but
it also reduces the duration of time required for fermentation. Particularly,
kimchi which uses large amounts of garlic has large amounts of carbon dioxide
and alcohol, thus improving its taste much more than other subsidiary materials
can. When red pepper powder is added, the fermentation of lactic acid is increased
and this fact supports the idea that garlic and red pepper powder accelerate
kimchi's maturation and fermentation. Ginger not only produces less flavoring
elements than other subsidiary materials, but also triggers the browning reaction.
On the other hand, salted seafoods contain large amounts of nitrogen which are
necessary for the growth of microorganisms. Such proteins and amino acids accelerate
kimchi's maturation. Salted shrimps accelerate maturation more than salted anchovies.
Therefore, when producing gimjang for the winter, which is to be stored for
a long time until the next spring, the salt concentration has to be higher while
the amount of salted seafoods and the red pepper powder supplement should be
less than in the kimchi to be stored for a short period, since they accelerate
maturation.
Cucumbers used as a subsidiary ingredient also accelerate its maturation. Alcohol-soluble
elements in cucumber juice facilitate the growth of lactobacillus plantarum,
since large amounts of the vitamin B group promote the growth of lactobacillus.
Carrots are also used as a subsidiary ingredient in kimchi to give better color.
But, since carrots contain enzymes which accelerate the oxidation of vitamin
C, it is recommended that less than 10 percent be added to kimchi. On the other
hand, large amounts of leeks are used for oisobagi (stuffed cucumber kimchi)
as they are alleged to delay maturation, but the fact has not been proven scientifically.
Leeks are used for cucumber kimchi as they are known to reduce the speed of
fermentation.
Nutrient Composition of Kimchi
Kimchi is a fermented vegetable food and an important side dish. It supplies
various nutritive substances for Koreans even during the winter time. Ingredients
used for kimchi are diverse, and the nutritive elements also vary according
to the stage of maturation. The characteristics of nutrients for kimchi are
low in calories, but high in water, cellulose and vitamins.
Green leaves of cabbage, radish and leafy radish, contain considerable amounts
of vitamin A. Therefore, it is desirable not to remove too much of the green
part. Red pepper contains plenty of vitamin A, only slightly less than carrots,
but carrots are not used as a kimchi ingredient because they have an enzyme
of ascorbinase which destroys vitamin C, so red pepper powder has become an
important source of vitamin A. At the same time, among kimchi's ingredients,
red pepper powder contains a large amount of vitamin C. Garlic has a sterilization
substance called allylsulfide which has a strong sterilization power and displays
various other effects. The spring onion also has sterilization element like
garlic, and its green part contains lots of vitamin A and C. Cucumbers contain
an element of bitter taste called elaterin and help digestion and urination
due to their calcium content. Salted shrimps or salted anchovies are a good
source of protein, amino acid and fat which are deficient in vegetables. These
salted seafoods are alkaline foods with a high calcium content and play the
role of neutralizing body fluids. Oysters are the most commonly used ingredients
for kimchi among seafoods; they are filled with calcium, iron and plenty of
glycogen and vitamins. Oysters have essential amino acids for the human body.
Glutamic acid and glycine in oysters produce a savory taste in kimchi.
The fermentation process of kimchi with various subsidiary ingredients changes
sugar to lactic acid and other organic acid products through the action of lactobacillus.
However, after a certain period, an excessive amount of acid is produced, pectin
which is dissolved due to the breeding of aerobic bacteria. Then an unpleasant
odor is generated, and the quality is damaged. The taste of kimchi varies according
to the concentration of salt and temperature during fermentation.
Production of Organic Acids
During
fermentation there is the biggest change in organic acid. The quantity of organic
acid products in kimchi varies according to the enzymes in vegetables or enzymes
secreted by various microorganisms during fermentation. It also varies according
to the combination of ingredients and temperature during fermentation, duration
of fermentation and salt concentration levels. When organic acids are analyzed
at different salt concentration levels, non-volatile organic acids such as lactic
acid, oxalic acid, malonic acid, succinic acid, malic acid, and citric acid
are produced, regardless of the salt concentration. But there is a difference
in quantity of acid production according to the salt concentration. At high
salt concentration levels kimchi produces less lactic acid and succinic acid
and more citric acid than at low salt concentration levels.
At the beginning of kimchi fermentation, malic acid is mostly contained in cabbages,
but in matured kimchi, lactic acid and succinic acid increase considerably.
There is no difference in the citric acid concentration at high temperatures
(22°C to 23°C) and at low temperatures (6°C to 7°C) during fermentation, but
at a low temperature, lactic acid and succinic acid are reported to be high,
while malic acid, oxalic acid, tartalic acid and malonic acid are reported to
be low.
Kimchi's organic acid also changes according to the duration of fermentation.
When kimchi is fermented at a low temperature (5°C), small amounts of lactic
acid and citric acid are produced at early stages and increase as time passes
by, while large amounts of malic acid at early stages decrease as time goes
by. Other acids such as oxalic acid, malonic acid and succinic acid do not change
according to the duration of fermentation.
Organic acid and carbon dioxide in kimchi are the two main elements which determine
the taste of kimchi. The amount of organic acid and carbon dioxide varies according
to the kind of microorganism, salt concentration and temperature, as has already
been explained. Kimchi fermented at a low salt concentration and low temperature
is found to have high acetic acid and carbon dioxide, and such a kimchi proves
to be more tasty.
Production of Free Amino Acids
Kimchi's unique taste is formed not only through organic acid,
carbon dioxide and seasonings, but also free amino acids.
Such free amino acid is produced by protein sources such as
salted oysters and meat. From the various kinds of kimchi,
17 kinds of amino acids are detected, and the total amount
of free amino acid is great in kimchi with salted anchovies.
Also, the kimchi's flavor appears to be far better in the
case of kimchi containing large amounts of lysine, aspartic
acid, glutamic acid, valine, methionine, leucine, and isoleucine.
On the other hand, matured kimchi shows large amounts of free
amino acids, and in particular glutamic acid, alanine, threonine
and serine. But arginine is found to be lower in matured kimchi
than in raw kimchi.
Production of Vitamins
Generally vegetables such as cabbages and radishes have vitamin C and carotene,
while the amount of the vitamin B group is much higher in marine products such
as salted sea foods. It is observed that the major source of vitamin C from
kimchi is red pepper and the vitamin B group from oysters. There is a variation
of the amount of vitamin B1 and B2 production in kimchi according to the stage
of fermentation. It is very low at an early stage, then increases to double
at the third week when it tastes good, and then decreases again to the level
of the early stage when it turns sour. Therefore, these vitamins are believed
to be synthesized by microorganisms during the process of fermentation, or separated
by the action of enzymes contained in kimchi ingredients. In the case of carotene,
the quantity decreases continually to the level of half of the early stage as
kimchi matures, when it starts to taste sour. On the other hand, niacin shows
a similar pattern to vitamin B1 and B2, but it decreases in the early stage
compared to those vitamins, and that is probably because it is consumed by another
fermented fungus.
The amount of vitamin C is low at the early stage of fermentation, then increases
a little bit and again decreases. Such a phenomenon is known to take place as
vitamin C is synthesized by sugar from the dissolution of pectin contained in
cabbage. The production is believed to be not by microorganisms but by the vegetables
own enzymes. During the first week, vitamin B1 and B2 decrease to half of the
early stage, but then increase rapidly to reach a maximum amount by the third
week.
In summary, the nutrient levels of kimchi vary according to the ingredients,
microorganisms and stage of fermentation. The amount of organic acid, free amino
acids and vitamins show the highest value when kimchi is well-fermented and
its flavor is good.
Prospectives in Kimchi -From Korean Traditional Kimchi to World Health Food-
Kimchi is a traditional Korean fermented food, rich in healthy biochemical and
microbiological properties, which contains various living microorganisms that
provide the human body with well-balanced nutrients.
Kimchi is a low-calorie, low-cholesterol vegetable food which is an important
source of dietary fiber and vitamins such as vitamin A, C, and vitamin B complex.
Kimchi also contains a high level of many kinds of minerals including calcium.
In addition, kimchi is known to have anticarcinogenic effect. The biosynthesis
of various microbes and enzymes enhanced by lactic fermentation improve digestion
and prevent constipation. Thus produced biochemicals also have antibacterial
and antimutagenic functions and, therefore, prevent cancer. Studies proving
such effects are reported in important papers such as Biochemical, Microbiological
and Nutritional Aspects of Kimchi - Korean Fermented Vegetable Products - (Critical
Reviews in Food Science and Nutrition, 34(2) : 175∼203 (1994)). This shows that
the study of kimchi as a health food is catching the attention of not only Korean
researchers but the world as well.
Of course, pickled vegetables are not an unique food type that can be found
only in Korea. In fact, according to regional differences such as natural conditions,
and social and cultural backgrounds, different people have developed different
kinds of pickled vegetables. For example, the Chinese have humchoy which is
pickled cabbage or cucumber. Japanese zukemono uses salt, soy sauce, vinegar
or rice bran to pickle vegetables. Other fermented vegetables known worldwide
include pickles, olives, cucumbers and German sauerkraut. However, what distinguishes
Korean kimchi from these fermented vegetables is that kimchi contains a rich
amount of healthy living microbes produced during fermentation and maturation.
Besides the nutritional aspects of kimchi, the various combinations of kimchi's
raw materials, and its preparation methods offer the world a variety of types
of kimchi that suit everybody's particular taste.
Indeed, people from all over the world have been enjoying kimchi's unique flavor
and aroma since it was selected as an official food in a number of international
events such as the 1988 Seoul Olympics and the 1998 World Cup. To preserve kimchi's
quality and reputation as a world-famous health food, the Korean kimchi industry
is upgrading its production process to meet international standards. Currently,
Korea exports kimchi to more than 36 nations, including Japan. But, considering
that an average Korean consumes 100-150g of kimchi per day, we can safely assume
that Korea's kimchi industry and the number of its importers will grow larger
and larger in the near future.
