CHAPTER 6
TYPICAL PRODUCTS OF BACTERIAL FERMENTATIONS

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Many products are produced by bacterial fermentations. These include the fruit and vegetable pickles produced by lactic acid fermentation and the products of alkaline bacterial fermentations. Lactic acid bacteria pickling is still carried out at the domestic scale. However industrial scale processes have been developed for the production of most types of pickles. Pickles can be made by storing prepared vegetables in a weak brine solution, by dry salting or allowing the vegetables to ferment without salt.

6.1 Dry salted pickles

Dry salting is used for pickling many vegetables and fruits including limes, lemons and cucumbers. For dry salt pickling any variety of common salt is suitable as long as it is pure. Impurities or additives can cause problems:

6.1.1 Dry salted lime pickle.

Location of production

Dry salted lime pickles are produced in Asia and Africa. They are particularly popular in India, Pakistan and North Africa.

Product Description

With dry salting, the limes are treated with dry salt. The salt extracts and juice from the vegetable and create the brine. The final product is a sour lime pickle. Spices are added depending on local preference. In India and Pakistan, the pickle is usually very spicy and hot due to the addition of chilli. It is usually eaten as a condiment.

Preparation of raw materials

The limes need to be selected and prepared. Only fully ripe limes without bruising or damage should be used. All limes need to be washed in potable cold water, drained, and then cut into quarters. Spices should be of good quality and free of mould.

Processing

Limes are placed in a layer, approximately 2.5 cm deep, into the fermenting container (a barrel or keg). One kilogram of salt is added for every four kilograms of limes. The salt is sprinkled over the vegetables. Another layer of vegetables is added and more salt added. This is repeated until the container is three quarters full. A cloth is placed above the vegetables and a weight added to compress the vegetables and assist in the formation of a brine. The formation of a brine takes about 24 hours. The container is then placed in the sun for a week.

As soon as the brine is formed, fermentation starts. As fermentation starts bubbles of carbon dioxide appear. Fermentation takes between one and four weeks depending on the ambient temperature. Fermentation is complete when no more bubbles appear. (Lal et al, 1986), (Kordylas,1990).

Flow diagram

Selection
Only ripe limes should be selected
Wash
In clean water
Cut
Cut into four pieces or slice the skin
Mix with salt
1kg salt for 4kg of limes
Ferment
Leave the container in the sun for a week to ferment
Package
 

Packaging and storage

The vegetables can be removed from the brine and packaged in a variety of mixtures which may consist of vinegar and spices or oil and spices. Lime pickle can be packed in small polythene bags and sealed or in clean jars and capped. Lime pickles keep well if stored in a cool place. Due to the high acid level of the final product, the risk of food poisoning is low (Fellows, 1997).

6.1.2 Pickled cucumbers

Location of production

Pickled cucumbers are made in Africa, Asia and Latin America.

Product description

Cucumbers undergo a typical lactic acid fermentation and change from a pale product to a darker green and more transparent product. Khalpi is a cucumber pickle popular during the summer months in Nepal (Karki, 1986).

Raw material preparation

Fully ripe cucumbers without bruising or damage are washed in potable cold water and drained. The cucumbers can be pickled whole or sliced. With khalpi the cucumbers are washed, sliced and cut into 5-8 cm pieces.

Processing

1 kg of salt is added to every 20 kg of small cucumbers and 15 kg of large cucumbers. The brine should be formed within 24 hours by osmosis. If the brine formed by osmosis does not cover the cucumbers 40o Salometer brine is added to the desired level. A day or two after the tank is filled and closed the brine should be stirred in order to help equalise the concentration of salt throughout the mass (Vaughn, 1985).

As soon as the brine is formed, fermentation starts and bubbles of carbon dioxide appear. Fermentation takes between one and four weeks depending on the ambient temperature. Fermentation is complete when no more bubbles appear.

During fermentation the brine becomes cloudy for the first few days due to the growth of bacteria. Later if the brine is not covered, a filmy yeast growth will often occur on the surface (Pedersen, 1979).

Flow diagram

Selection
Only ripe cucumbers should be selected
Wash
In clean water
Mix with salt
1kg salt for 15-20kg of cucumbers
Ferment
For between one and four weeks
Package
 

Packaging and storage

Cucumber pickle is usually stored in clean capped jars. They keep well if stored in a cool place. Due to the high acid level of the final product, the risk of food poisoning is low. With khalpi in Nepal, oil is added.

6.1.3 Pak-Gard-Dong (Pickled leafy vegetable)

Pak-Gard-Dong is a fermented mustard leaf (Brassica juncea) product made in Thailand. The mustard leaves are washed, wilted in the sun, mixed with salt, packed into containers for 12 hours. The water is then drained and a 3% sugar solution added. They are again allowed to ferment for three to five days at room temperature. Micro-organisms associated with the fermentation include Lactobacillus brevis, Pediococcus cerevisiae and Lactobacillus plantarum (Boon-Long, 1992).

A similar product (Hum choy) is made in the South of China. This is produced by fermenting a local leafy vegetable. The leaves are washed and drained. They are then covered in salt and hung on racks to dry in the sun. The wilted leaves are placed in earthenware pots and covered with rice water, obtained after washing rice grains. The pots are sealed and the leaves allowed to ferment for four days. The product can be stored for up to two months if the seal is not broken (Steinkraus, 1996).

6.1.4 Tempoyak (pickled durian)

Tempoyak is the fermented pulp of a durian fruit (Durio zibethinus) from Malaysia. It has the distinctive durian smell and a creamy yellow colour. It is made by mixing durian pulp with salt and placing in a sealed container. Fermentation takes about seven days.

6.1.5 Pickled beetroots

In Russia beetroot is pickled by cleaning, slicing and placing in a container with salt. Due to the high sucrose level, dextrans are produced giving the product a slimy texture (Pedersen, 1979).

6.1.6 Lamoun Makbous (pickled lemons)

Pickled lemons are popular in Asia. In west Asia and north Africa they are known as lamoun makbous and msir. Lemons are washed in clean water, sliced and covered in salt. After at least 24 hours, they are drained and mixed with oil and spices.

6.2 Brined fruit and vegetable pickles

For brine pickling any variety of common salt is suitable as long as it is pure. Impurities or additives can cause problems:

6.2.1 Green Mango Pickle.

Location of production

Mango pickle is a very popular pickle in many Asian, African and Latin American countries. It is a major product of India, Pakistan and Bangladesh and it is estimated that the annual production of mango pickle in South Africa is over 10,000 tons (Redelinghuys and Van der Riet, 1978).

Product description

Green mango pickle is a hot, spicy pickle with a sour taste. It is eaten as a condiment. Preservation is caused by a combination of salt, increased acidity and to a small extent the spices. It is known as burong mangga and dalok in the Philippines.

Preparation of the raw material

The fresh, fully mature, firm but unripe mangoes must be carefully selected to ensure a good quality product. The best pickles are obtained from fruit at early maturity when the fruit has reached almost maximum size. Riper fruit results in pickles with a fruity odour and lacking the characteristic and predominant green mango flavour.

The green mangoes need to be inspected and any damaged fruit rejected. The fruit is washed in clean water and drained.

After draining, the fruit is cut. Sharp knives with preferably stainless blades should be used. Iron or copper equipment should be avoided. A single stroke should be used during the cutting process to ensure minimum damage and avoiding mushiness in the final product.

Processing

The sliced mangoes are soaked in brine solution. Sodium metabisulphite (1000 ppm) and 1% calcium chloride are added. The containers are stored until the mangoes are pickled. The brine is then drained off and spices are mixed with the mango slices (Redelinghuys and Van der Riet, 1978).

Flow diagram

Fruit
The mangoes need to be unripe
Sort
Remove damaged fruit
Wash
With clean water.
Drain
 
Cut
Stainless steel knives should be used
Soaked in brine
20% salt solution
Drain
Spices to taste
Add spices
 
Pack
Pack in containers and add oil

Packaging and storage

The mixture is then packed and oil added onto the surface of the mixture. The mangoes should be firmly pressed down in the container. Good quality vegetable oil such as sunflower oil should be used and finely ground chilli powder can be added to the oil for flavour and colour. Mango pickle can be packed in small polythene bags and sealed or in clean jars and capped. Mango pickle keeps well if stored in a cool place. If it is processed well, it can be kept for several months. Due to the high acid level of the final product, the risk of food poisoning is low (Fellows, 1997).

6.2.2 Lime pickle (brined).

Location of production

Lime pickles are produced in Asia, Latin America and Africa. They are particularly popular in India, Pakistan and North Africa.

Product description

Lime pickle is made from salted pieces of lime packed in a salty, spicy liquor, like a semi-solid gravy. It is brownish red and the lime peels are yellow or pale green with a sour and salty taste. It is eaten as a condiment with curries or other main meals. If processed well, the product can be kept for several months.

Preparation of raw materials

The limes need to be selected and prepared. Only fully ripe limes without bruising or damage should be used. All the limes need to be washed in potable cold water and drained. The limes are dipped in hot water (60-650C) for about five minutes. They are then cut into pieces in order to expose the interior and allow salt to be absorbed more quickly.

All spices should be of good quality and free of mould.

Processing

The prepared limes are covered with a brine solution. This causes water to be drawn out of the pieces by osmosis. It is important to ensure that the surface is covered with juice, and leave for 24 hours. If necessary, the fruits should be pressed down to hold them below the liquid. Once the limes have been placed in the brine, there is a rapid development of micro-organisms and fermentation begins.

After fermentation the limes are dried in the sun until the skin becomes brown.

Flow diagram

Sort
Select ripe (but not overripe) healthy lime fruits
Wash
 
Heat
Dip in hot water (60-650C) for about five minutes
Cut
Cut into four pieces or alternatively cut into smaller, uniform-sized pieces
Brine
Ensure that the surface is covered with juice
Dry
Dry in the sun for 2-3 days
Mix spices
To local preference
Pack
 
Store
In a cool place, away from sunlight

Packaging and storage

The limes are mixed with spices and oils according to local taste and tradition. Lime pickle can be packed in small polythene bags and sealed or in clean jars and capped. Lime pickle keeps well if stored in a cool place. Due to the high acid level of the final product, the risk of food poisoning is low.

6.2.3 Kimchi (pickled cabbage)

Location of production

Kimchi is probably the most important processed food product in Korea. It is an essential dish, eaten at most mealtimes. Production is estimated at over one million tons, mainly at household level. Daily consumption is estimated at 150 to 250 grams per person.

Product description

Kimchi is a general name for a range of closely related fermented products. It is similar to Sauerkraut in Europe and the United States. There are numerous variations of kimchi depending on the production technique. The main pickled cabbage kimchis are tongbaechu-kimchi tongkimchi and bossam-kimchi. This section refers to kimchi produced from cabbage, the following section deals with pickled radish products.

Preparation of raw materials

Appropriate cultivars of Chinese cabbage, with light-green coloured soft leaves and compact structures with no defects, are required for production of kimchi. After removing outer leaves and roots from the cabbage, it is cut into small pieces.

Processing

The prepared cabbage is placed in a salt solution (8-15%) for two to seven hours in order increase the salt content of the cabbage to between 2.0-4.0% (w/w). It is then rinsed several times with fresh water and drained to remove extra water by centrifugation or by allowing to stand.

Kimchi fermentation is carried out by various micro-organisms present in the raw materials and ingredients used in the preparation of kimchi. Among the two hundred bacteria isolated form kimchi, the important micro-organisms in kimchi fermentation are known to be Lactobacillus plantarum, L. Brevis, Streptococcus faecalis, Leuconostoc mesenteroides and Pediococcus pentosaceus.

After fermentation, the product can be left to mature for several weeks if refrigeration is available. If stored under warm conditions, the kimchi deteriorates rapidly.

Flow Diagram

Korean cabbage
 
Cut
Cut into four parts
Add brine
5% for 12 hours or 15% for 7hours
Rinse
Drain water
Mix
With salt, spices and flavourings
Ferment
 

6.2.4 Green olives

Olives are a brine fermented product which undergo an essential pre-treatment with lye to remove substances which are toxic to bacteria and would, if left in the olives, prevent fermentation.

Green olives are placed in a 2% sodium hydroxide (lye) solution at 210 to 240C until the lye penetrates the flesh. Cold water is added to the solution, which, dilutes the mixture until the lye is completely removed. The lye treatment is necessary to remove a bitter glucoside compound (oleuropein) from the outer tissues of the olive. Oleuropein is highly toxic to bacteria and therefore needs to be removed in order for a fermentation to take place. After the glucoside has been removed, the olives are placed in barrels with a 1 to 10% brine solution and allowed to undergo a spontaneous fermentation. The optimum fermentation temperature is 240C. The fermentation period usually takes between two and three months. Once fermentation is complete, the olives are packed in airtight jars and sterilised which produces a good quality product with a long storage life.

6.2.5 Black olives

When ripe olives are used, they are placed in a 5 to 7% brine solution to soften the outer tissue before lye is added. This pre-treatment allows the lye to penetrate the fruit more easily. In ripe fruit, the glucoside is situated more deeply within the tissue. After soaking in brine, the lye solution (0.7 to 2.0%) is added and, after soaking, the olives are washed clean. They are then packed in barrels with a 2 to 5% brine solution and allowed to undergo fermentation for two to six weeks, depending on the external temperature. Unlike immature olives, the ripe one are exposed to air during fermentation. This is to oxidise the polyphenols in the tissue to a black colour, which is dependent upon oxygen and the small amounts of sodium hydroxide which are left on the olives. The finished product is packed in a 3 to 5% brine solution and then sterilised. Bacillus subtilis may produce pectolytic enzymes which result in a soft product. If the wash water used for removing the lye is below 600C, many species of undesirable bacteria can survive which result in a low quality product.

6.2.6 Jack-fruit pickle

Young green jack fruit is pickled in India and Sri Lanka. Young green jack fruit are peeled and cut into 1.2 to 1.8 cm thick slices. The slices are placed in a container and covered in an 8% common salt solution. They are weighed down to keep them submerged in the brine. The brine solution is increased by 2% each day until it reaches 15%. The slices are then left for 8-10 days in the brine. Vinegar and spices are added prior to packaging (Lal, Siddappa, and Tandon, 1986).

6.2.7 Pickled Radish

A number of pickled radish products are produced in Korea. These include: kaktugi, tongchimi,chonggak-kimchi, seokbakji, yolmu-kimchi dan moogi kach doo ki gactuki and mootsanji.

6.2.8 Pickled cucumber

A variety of brine pickled cucumber products are made around the world. Oi sobagi and oiji are made in Korea. In Egypt cucumbers are pickled by soaking in brine to produce torshi khiar.

6.2.9 Pickled leafy vegetables

There are many other brine pickled leafy vegetables around the world. For instance:

6.2.10 Other pickled vegetables and fruits

6.3 Non salted lactic acid bacteria products

6.3.1 Gundruk (pickled leafy vegetable)

Location of production

Gundruk is particularly popular in Nepal. The annual production of gundruk in Nepal is estimated at 2,000 tons and most of the production is carried out at the household level.

Product description

Gundruk is obtained from the fermentation of leafy vegetables in Nepal. It is served as a side dish with the main meal and is also used as an appetiser. Gundruk is an important source of minerals particularly during the off-season when the diet consists of mostly starchy tubers and maize which tend to be low in minerals (Karki, 1986).

Preparation of raw materials

In the months of October and November, during the harvest of the first broad mustard, radish and cauliflower leaves, large quantities of leaves accumulate - much more than can be consumed fresh (Aidoo, 1986). These leaves are allowed to wilt for one or two days and then shredded with a knife or sickle.

Processing

Shredded leaves are tightly packed in an earthenware pot and warm water (at about 30oC) is added to cover all the leaves. The pot is then kept in a warm place. After five to seven days, a mild acidic taste indicates the end of fermentation and the gundruk is removed and sun-dried. This process is similar to sauerkraut production except that no salt is added to the shredded leaves prior to gundruk fermentation. The ambient temperature at the time of fermentation is about 18oC (Jones, 1994), (Karki, 1986).

Pediococcus and Lactobacillus species are the predominant micro-organisms during gundruk fermentation. The fermentation is initiated by L. cellobiosus and L. plantarum, and other homolactics make a vigorous growth from the third day onwards. Pediococcus pentosaceus increases in number on the fifth day and thereafter declines (Karki et al,1983). During fermentation, the pH drops slowly to a final value of 4.0 and the amount of acid (as lactic) increases to about 1% on the sixth day.

It has been found that a disadvantage with the traditional process of gundruk fermentation is the loss of 90% of the carotenoids, probably during sun-drying. Improved methods of drying might reduce the vitamin loss (Aidoo, 1992).

Flow diagram

Leafy vegetables
 
Wilt
One to two days
Shred
 
Placed in earthen pot
The leaves need to tightly packed
Cover the leaves
Cover the leaves with warm water and straw
Ferment
The pot is kept warm in the sun and by a fire by night
Add warm water
To keep the pot warm
Dried
Product dried on mats in the sun

6.3.2 Kocho (pickled false banana)

Location of production

Ethiopia

Product description

False banana (Ensete ventricosum) is fermented in a pit to produce a pulp known as kocho. Foods preserved in pits can last for years without deterioration. Pits therefore provide a good, reliable cheap means of storage.

Processing

The type of soil and its drainage are important in the selection of a pit site. Pits are often lined with stones to prevent the soil from the side walls falling into the bottom. A family pit may be 0.6 to 1.5 metres deep and 1.2 to 2 metres wide with a capacity of about fifty breadfruits. A community pit is usually much larger, with the capacity to hold up to 1000 breadfruit. A family pit requires at least 1000 green banana leaves and four sacks of dried banana leaves for lining the walls and top. It is essential that proper attention is given to hygiene of the pit and the fruit to be stored in it.

The central stems are removed from fresh banana leaves and they are wilted in the sun until they become soft and pliable. The pit is lined with dry leaves, then green leave are folded and arranged, overlapping each other, around the sides of the pit and extending over the top. At lest two or three layers of banana leaves are used to seal the pit and prevent contamination by the soil. Washed, peeled food is placed in the pit, green banana leaves are folded over the top of the food and heavy stones are placed on top to weigh down the leaves.

Root crops and bananas are peeled before placing in the pit, breadfruit are scraped and pierced. Food is left to ferment for three to six weeks, after which time it becomes soft, has a strong odour and a paste-like consistency. The fermented paste can be left in the pit and removed as required. Usually, it is removed and replaced with a second batch of fresh food to ferment. The fermented food is washed and fibrous material removed. It is then dried in the sun for several hours to remove the volatile odours. It is then pounded into a paste. Grated coconut or coconut cream and sugar added and the mixture is wrapped in banana leaves and either baked or boiled (Steinkraus, 1996).

During fermentation, carbon dioxide builds up in the pit, creating an anaerobic atmosphere. As a result of bacterial activity, the temperature rises much higher than the ambient temperature. The pH of the fruit within the pit decreases from 6.7 to 3.7 within about four weeks. Inoculation of the fruit in the pit with lactic acid bacteria greatly speeds up the process.

In the South Pacific pit fermentations are an ancient method of preserving starchy vegetables such as banana, plantain, breadfruit, cassava, taro, sweet potato, arrowroot and yams. The products undergo an acid fermentation, to produce a paste with good keeping qualities. It is usually pounded with a little sugar, coconut cream or fresh coconut and boiled or baked to make a type of pudding.

6.3.3 Sinki (pickled radish)

Sinki is a sour pickle prepared from radish tap roots. It is consumed traditionally in India, Nepal and parts of Bhutan, where it is used as a base for soup or eaten as a pickle. It is one of the most popular pickles in Nepal. Fresh radish roots are harvested, washed and wilted by sun-drying for one to two days. They are then shredded, re-washed and packed tightly into an earthenware or glass jar, which is sealed and left to ferment. The optimum fermentation time is twelve days at 30ºC. Sinki fermentation is initiated by L. fermentum and L. brevis, followed by L. plantarum. During fermentation the pH drops from 6.7 to 3.3. After fermentation, the radish substrate is sun-dried to a moisture level of about 21% (Steinkraus, 1996). There is a second processing method involving fermentation in a clay lined pit for two to three months (Karki, 1986). For consumption, sinki is rinsed in water for two minutes, squeezed to remove the excess water and fried with salt, tomato, onion and green chilli. The fried mixture is then boiled in rice water and served hot as soup along with the main meal (Steinkraus, 1996).

6.3.4 Sunki

Sunki is a non-salted and fermented vegetable product prepared from the leaves of "Otaki-turnip" in Kiso district, Nagano prefecture, Japan. Sunki is eaten with rice and in miso soup. The Otaki-turnip is boiled, inoculated with "Zumi" (a wild small apple) dried Sunki from the previous year and allowed to ferment for one to two months. Sunki is produced under low temperature (in winter season). Micro-organisms involved include Lactobacillus plantarum, L. Brevis, Bacillus coagulans and Pediococcus pentosaceus (Makayama,1957).

6.3.5 Kanji

In Northern India and Pakistan carrots, especially a variety that is deep purple in colour, are fermented to make a traditional ready to serve drink known as kanji. Kanji is very popular and considered to have cooling and soothing properties and to be of high nutritional value. After thorough washing the carrots are finely grated. Each kilogram of grated carrot is mixed with 7 litres of water, 200g of salt, 40g of crushed mustard seed and 8g of hot chilli powder. The mixture is then placed in a glazed earthenware vessel, which is almost entirely sealed, leaving only a tiny hole for gases released during fermentation to escape. The mixture is then allowed to ferment for seven to ten days. The type of fermentation that takes place is known as a lactic fermentation, which must be carried out in the absence of air. Lactic acid bacteria produce lactic acid which reduces the pH (ie increases the acidity) to a level that prevents the growth of food poisoning organisms. The final product is slightly acidic in taste and has an attractive purple-red colour. After fermentation the drink is strained through fine muslin and has to be consumed within 3 or 4 days after which it goes bad. Each kg of grated carrot yields just over 7 litres of kanji (Berry, 1998), (Shah, 1986).

6.3.6 Fermented tea leaves

In South East Asia, tea leaves (Camellia sinensis) are fermented to make a sour-tasting snack. In Myanmar the product is called leppet-so, in Thailand it is known as miang.

6.4 Alkaline bacterial products

6.4.1 Kawal.

Location of production

Sudan

Product description

Kawal is a strong smelling Sudanese, protein-rich food prepared by fermenting the leaves of a wild African legume, Cassia obtusifolia and is usually cooked in stews and soups. It is used as a meat replacer or a meat extender. Its protein is of high quality, rich in sulphur amino acids which are usually obtained from either fish or meat (Dirar, 1992).

Raw material preparation

The Sickle Pod plant (Cassia obtusifolia) is a wild legume that grows in Sudan. The leaves are collected late in the rainy season when the plant is fully grown. All the stems, pods and flowers are removed. The leaves are not washed, since it is thought that natural micro-organisms on the leaves are important for the correct fermentation.

Process and principles of preservation

The leaves of the leguminous plant are pounded into paste without releasing the juice. The paste is placed in an earthenware jar and covered with sorghum leaves. The whole jar is sealed with mud and buried in the ground up to the neck in a cool place. Every three days the contents are mixed by hand.

The fermentation takes about fourteen days. The fermentation is extremely complex. The main micro-organisms are Bacillus subtilis and Propionibacterium spp. Lactic acid bacteria including Lactobacillus plantarum; yeasts including Candida krusei and Saccharomyces spp and moulds including Rhizopus spp are also involved.

After about fourteen days, the strongly smelling black fermented paste is made into small balls and sun-dried for five days. (Harper and Collins, 1992) , (Aidoo,1986).

Flow diagram

Select leaves
Remove stems and flowers
Grind leaves
Pound the leaves into a paste in a mortar and pestle
Place in jar
With sorghum leaves
Cover jar
 
Bury jar
Bury up to the neck
Mix
Every three days
Roll into balls
 
Sun dry
Three to five days

6.4.2 Ombolo wa koba

In Zaire cassava leaves are fermented to produce ombolo wa koba which is traditionally eaten with boiled cassava and plantain bananas. Cassava leaves are allowed to wilt and turn black. This takes about three to four days. The cassava leaves are then chopped up and placed in a pot of boiling water for about one hour. During this processing stage, a water soluble extract of ash is produced by placing the ash of burnt dried banana skins and palm tree flowers in a strainer and pouring water through it. The extract is then added to the boiled cassava leaves. The extract is alkaline and neutralises the cyanhydric acid liberated when the leaves are chopped up (Jones et al, 1996). Salt and dried fish or meat is also added. After allowing the cassava leaf mixture to cool a little, acid palm oil is then added. This reacts with the excess alkali and neutralises it. The product is now ready to be eaten (Menea and Bishosha).

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