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Indigenous fermented-food technologies for small-scale industries
Keith H. Steinkraus
Professor of Microbiology, Institute of Food Science, Cornell
University, Geneva, New York, USA
INTRODUCTION
Hunger and poverty go hand in this world where vast millions must support their families on less than US$1 per day. Protein-calorie malnutrition is common in the developing world, and it leads not only to stunting of physical growth but to retardation of brain growth and mental development. Malnutrition also leads to lower resistance to infectious disease, higher death rates, and lower productivity in the work force. Vitamin A deficiency leads to xerophthalmia and tragic blindness in at least a million children every year (19, 6).
What can be done to alleviate the nutritional problems that face the developing world? The Green Revolution has resulted in a vast increase in world-wide productivity of rice and wheat and has enabled mankind to more or less continue to feed its burgeoning population until now. The Green Revolution, however, has not relieved the hunger and malnutrition of millions in the developing world. The basic problem remains essentially economic: Food is generally available if people have the money to buy it, and farmers the world over will produce more food if they can sell it for a profit. At present we have no way of improving the economic status of the millions of malnourished people, unless the world should unexpectedly decide to use the 350 billion dollars spent each year on armaments (100 billion of which is spent by the Third World countries) on improving the economic and nutritional status of humankind (13).
The indigenous fermented foods constitute a group of foods that are produced in homes, villages, and small cottage industries at prices within the means of a majority of the consumers in the developing world. Examination of these foods may, therefore, provide clues as to how food production and preservation can be expanded and thereby contribute to improved nutrition in the developing world in the future.
Some indigenous food fermentations such as soy sauce (shoyu), Japanese miso, Indonesian tempe, Indonesian tape ke ten, Japanese sake, Indian idli and dosai, and fish and shrimp sauces and pastes have been intensively studied to determine optimum conditions for fermentation, the essential micro-organisms, the biochemical, nutritive, and flavour/texture changes that occur during the fermentation, and possible toxicological problems that can arise (25).
The huge international enzyme industry today can be traced directly to the indigenous Chinese and Japanese soy-sauce and Japanese miso and sake fermentations. The monosodium glutamate (MSG) industry and the relatively recent but significant nucleotide flavour-enhancing industry also are outgrowths of soy-sauce fermentation. Soy sauce, miso, and sake have become giant, heavily commercialized industries. Fish and shrimp sauces and pastes are produced industrially in Burma, South Vietnam, Thailand, and the Philippines and on a smaller scale in other countries of SouthEast Asia. Tempe is produced commercially in Indonesia and Malaysia. It also is produced by at least 53 small factories in the United States (22), and it is destined to become an important meat substitute at least among the American vegetarian community, which numbers an estimated 15,000,000 at present.
CLASSIFICATION OF INDIGENOUS FOOD FERMENTATIONS
Indigenous food fermentations have been classified as follows
(26):
- fermentations involving proteolysis of vegetable proteins by
microbial enzymes in the presence of salt and/or acid with
production of amino acid and peptide mixtures with a meat-like
flavour (examples are soy sauce, Indonesian kocap, miso, and
Indonesian tauco);
- fermentations involving enzymic hydrolysis of fish and shrimp
or other marine animals in the presence of relatively high salt
concentrations to produce meatflavoured sauces and pastes;
- fermentations producing a meat-like texture in a
cereal-grain-legume substrate by means of fungal mycelium that
knits the particles together (examples are Indonesian and
Malaysian tempe kedela, Indonesian oncom (ontjom) kacano. oncom
tahoo. and tempe bonakrek);
- fermentations involving the koji principle, in which
microorganisms with desired enzymes are grown on a cereal-grain
or legume substrate to produce koji, a crude enzyme concentrate
that can be used to hydrolyse particular components in the
desired fermentation (this category includes soy sauce, miso,
kecap, tauco, tempe, oncom, tape, and rice wines such as sake);
- fermentation in which organic acids are major products (this
category includes Korean kimchi, sauerkraut, fermented milks and
cheeses, African ogi and uji, idli, dosai, tape, and also tempe,
in which acidification occurs during the initial soaking of the
soybeans),
- fermentations in which ethanol is a major product (this
category includes rice wines, palm toddies, sugar cane wines,
beers, and, very important nutritionally, tape ketan and tape
ketela).
There is considerable overlap among the various categories of fermentation, but the classification does facilitate description and analysis of the potential usefulness of the various fermentations.
Examination of the various classifications indicates that food fermentations could be used to establish the following small-scale food-processing operations:
- production of meat-like flavours from vegetable proteins
(soy sauce and miso),
- production of meat-like flavours from fish and shrimp and other
marine animals (fish and shrimp sauces and pastes),
- production of meat-like textures in cereal-legume substrates
(tempe and oncom),
- production of highly starchy foods with improved protein
content (tape ketan and tape ketela),
- production of foods with improved vitamin content (tape, tempe,
and oncom),
- production of leavened bread-type foods without the use of
wheat or rye (idli and dosai),
- production of quick-cooking food (tempe and oncom).
PRODUCTION OF MEAT-LIKE FLAVOURS FROM VEGETABLE PROTEINS
Foods are generally sought after and consumed on the basis of their desirable aromas, textures, and flavours. People like foods that taste good. Meats have high prestige and are expensive, but excellent, sources of proteins and other nutrients. There is not at present enough meat in the world to supply the world's nutritional needs for protein at prices the consumer can afford to pay. Even in Australia, which is noted for its high consumption of meat, Marmite and Vegemite, acid-hydrolysed yeast products with a meatlike flavour, are widely consumed as a spread for bread and as an ingredient in soups. In the United States, where meat dishes are the mainstay of the diet, nearly every home now has its bottle of soy sauce used to add meat flavour to various dishes. In Africa, where meats are a minor part of the diet, bouillon and Maggi cubes are consumed by the billions. There is a considerable need for meat flavours and the amino acids and peptides in meatflavoured sauces and pastes for modifying and formulating foods in the diets of people in the developing world. A small-scale industry can be based on the production of meat-like flavours.
Soy Sauce (Shoyu) and Miso Fermentations
The Chinese thousands of years ago showed the world how to produce meat-like flavours from vegetable protein, which was one of the great discoveries in food science and which may become of even greater importance in the future. The soy sauce and miso fermentations were originally household fermentations, and they continue to be so in parts of the Orient today even though the products are also manufactured industrially in very targe quantities (21, 3337).
Miso has been made in the home and on the farm since A.D. 1600 in Japan (20). Indigenous miso manufacture is a very interesting process. Soybeans are soaked, cooked, mashed, and then formed into balls. The balls are tied together with rice straw and suspended above a stove or heater for about 30 days, during which time the balls become overgrown with moulds naturally present in the environment. The balls are then brushed, mixed with water and salt, and packed into crocks where fermentation continues for a year or longer. The resulting meat-flavoured paste is a primitive miso. Free liquid is used as a soy sauce.
At present, the Japanese use a koji for the manufacture of both soy sauce and miso. For soy sauce, the koji is prepared by overgrowing soaked, cooked, cooled soybeans coated with ground roasted wheat with moulds belonging to the Aspergillus oryzee species. Production of the koji is essentially a solid-state fermentation. The soy-sauce koji contains proteases, amylases, and lipases that hydrolyse their respective substrates in the subsequent submerged fermentation in 18 per cent weight per volume salt brine. During the submerged fermentation, Pediococcus cerevisiae, Lactobacillus delbruekii, and salt-tolerant Saccharomyces rouxii develop.
For miso, the koji is prepared from rice, barley, or soybeans. The fermenting organism again is Aspergillus oryzee. Following overgrowth of the mould, the koji is mixed with hydrated, cooked soybeans and salt. Miso is essentially in a solid state during its entire fermentation. Hesseltine and Shibasaki (9) demonstrated that the only micro-organism essential for the miso fermentation (in addition to the mould Aspergillus oryzee) was Saccharomyces rouxil, which develops when the pH of the mash has fallen to below 5.0. However, miso from an earlier fermentation can be used to inoculate a new fermentation (at the time of mixing the koji with salt and soybeans).
The satt content in various misos varies from 5.5 to 13 per cent weight per volume in fresh miso (20). Sweetness depends on the proportion of cereal koji added to the soybeans (4). Colour depends in part on the total cooking time given the soybeans and the length and temperature of fermentation. The higher the salt content, the slower the proteolytic hydrolysis and the better the miso keeps (31).
Both soy sauce and miso are highly industrialized in Japan. Yet, by their nature, both fermentations can be conducted on a small scale at the cottage-industry level or even in the home. In the miso-dame process, the fermentation depends on moulds naturally present in the environment and on the straw used to tie the soybean-mash balls. In some places in the Orient soy-sauce manufacturers today rely on the moulds present in wheat flour to produce a soy-sauce koji.
More recently, soy sauce has been manufactured by hydrolysing soybeans with concentrated hydrochloric acids and neutralizing the product with sodium hydroxide. While this does yield a meat-like flavour, the alcohols, organic acids, and esters produced by the fermentation process are lacking and the acid-hydrolysed sauce does not have the aroma and flavour of the genuine fermented sauce. Also, tryptophan is destroyed during acid hydrolysis, resulting in a loss of nutritive value.
The soy-sauce-miso process is used to produce meat-like flavours from soybeans, wheat, rice, and barley substrates. It could probably be adapted to other substrates, such as coconut and yeast, which yield meat-like flavours by acid hydrolysis. These meat-flavoured sauces and pastes could improve the nutrition and diets in many developing countries. The demand would support small-scale factories in most countries.
FISH AND SHRIMP SAUCES AND PASTES
While soy sauce was developed in northern Asia, the South East Asians made an equally great discovery concerning how to convert small, surplus fish and shrimp into meat-flavoured sauces and pastes. In fact, the soy-sauce and fish sauce fermentations both depend on proteolytic enzymes to hydrolyse the proteins in the substrate to the constituent amino acids and peptides. In soy sauce, fungal enzymes are used, while in fish sauce, enzymes in the fish tissues, particularly the gut tissues, are involved. Both fermentations are carried out in concentrated salt brine (18 per cent for soy sauce; 23 per cent or higher for fish sauce). In their highest qualities, soy sauce and fish sauce are quite comparable in flavour: both are similar to beef broths. The processes are amenable to the use of surplus marine animals of many types (non-commercial) and could serve as a base for small-scale factories.
Over the past few years a number of accelerated processes for manufacturing fish sauces and pastes have been developed. Some of these involve the addition of vegetable proteases such as bromeli or papain to the fermenting fish (1). Ismail (11, 12) developed a "rapid" process for fish sauce in which he produced a koji by growing selected strains of Aspergillus oryzee on soybeans and then mixing the koji with an equal weight of fish, thus effectively producing a fish-soy sauce.
Many new products are technologically possible by combining known fermentations with new substrates or new microorganisms. Much of the world has not as yet adopted fishshrimp sauces or pastes to its diet, although they present an excellent opportunity to utilize surplus marine animals as substrates. The processes offer an opportunity to entrepreneurs who wish to start new businesses wherever surplus marine animals are available.
MEAT SUBSTITUTES (ANALOGUES)
Large Western food companies have invested millions of dollars in developing processes by which soybean protein is extracted and concentrated to purities above 90 per cent and then by chemical modification and extrusion through platinum dies spun into protein strands which can be formed into pieces with meat-like texture. With added fats and meat flavors, the products are called meat analogues (a sophisticated name for imitation meats) and there is no doubt that these vegetable protein products will be an important part of "meat" consumption in the Western world in the future. Several products are already on the market (8, 18, 23, 30).
Similarly, large meat packers have developed processes in which soybeans are flaked, tempered, formulated, and extruded so that the products are subjected to high pressure and temperature for a short time and emerge from the extruder as chewy, protein-rich, meat-like nuggets that supply the flavour, texture, and nutritive value of meats in a number of Western dishes. In England, Rank, Hovis, and McDougall developed a process wherein mould mycelium is grown on low-cost carbohydrate, recovered by filtration, and formulated with added fat, flavour, and other components to produce meat analogues in which the mould mycelium provides the fibrous texture (24). This process entails modern sophisticated food science and technology.
It is interesting that the Western world, which consumes so much meat, has developed these advanced processes for manufacturing vegetable-protein meat substitutes.
Indonesian Tempe Kedele
The Indonesians centuries ago, without modern chemistry and microbiology, developed a fermentation process for making meat analogues from soybeans in which the mould mycelium provides the meat-like texture. The product, called tempe kedele, is manufactured by small-scale cottage industries, which could be established in any developing country where soybeans are available.
Tempe kedele is a white, mould-covered cake produced by fungal fermentation of dehulled, hydrated (soaked), and partially cooked soybean cotyledons. The mould grows throughout the bean mass, knitting it into a compact cake that can be sliced thin and deep-fat fried or cut into chunks and used as a protein-rich meat substitute in soups. The essential moulds belong to the genus Rhizoous; Rhizoous oligosporus is the species identified as most characteristic and best adapted for production of tempe (7, 27).
The essential steps in the production of tempe are the following:
- cleaning the soybeans,
- hydration and acid fermentation,
- dehulling dry or following hydration,
- partial cooking,
- draining, cooling, surface drying,
- placing the soybean cotyledons in suitable fermentation
containers,
- inoculating with tempe mould (before or after placing in the
fermentation container),
- incubating until the cotyledons are completely covered with
mould mycelium,
- harvesting and selling,
- cooking for consumption, either by frying in deep fat or by use
as an ingredient in soups in place of meat.
Traditional Tempe Fermentation
The soybeans are washed and soaked in water overnight, during which time they undergo bacterial acid fermentation reducing the pH to 5.0 or lower. An alternate process is to place the soybeans in water, bring it to a boil, and then allow the beans to soak overnight. The general purpose of the boiling is to facilitate removal of the hulls. The hulls are loosened by rubbing the soaked beans between the hands or stamping them with the feet and are then floated away with water. The cotyledons are then given a short boil, cooled, surface-dried by winnowing, and inoculated with tempe mould either from a previous batch of sound tempe or from mould grown and dried on leaves. Traditionally, the inoculated cotyledons are then wrapped in small packets using wilted banana or other large leaves and are incubated in a warm place for two or three days, during which time they are competely overgrown by the mould mycelium. The tempe is then ready for cooking (27).
Industrial Production of Tempe
Twenty years ago most tempe was prepared for sale using the traditional process described above. Then research in the United States resulted in some improvements in medium-scale processing of tempe. Steinkraus et al. (28) described a pilot-plant process in which the soybeans were dehulled dry by passing them through a properly adjusted burr mill. Preceding the burr mill, the beans were given a short heat treatment at 104°C (220°F) to shrivel the cotyledons. The hulls were then removed from the cotyledons by passing them through an aspirator or over an Oliver gravity separator. Alternatively, the beans were soaked and dehulled wet by passing them through an abrasive vegetable peeler. Acidification of the beans, considered to be an essential step, particularly in large-scale processing, where invasion by foodspoilage organisms could ruin large batches, was accomplished by adding 1 per cent weight per volume of lactic acid to the soak and cook water. The partially cooked beans were then drained, cooled, and inoculated with powdered, pure-culture tempe mould grown on sterilized soybeans and freeze-dried. The inoculum was mixed with the drained, cooled cotyledons in a Hobart mixer. The inoculated beans were then spread on dryer trays (35 x 81 x 1.3 cm), covered with a layer of wax paper, and incubated at 37°C (98.6°F) and 90 per cent relative humidity. By this procedure, fermentation was complete in less than 24 hours. The tempe was cut into 2.5 cm squares, and the dryer trays were placed in a circulatinghot-air dryer at 104°C (220 F), dehydrated to less than 10 per cent moisture, and packaged in polyethylene bags for distribution.
Within a few years, the commercial tempe industry in Indonesia had adopted wooden trays with dimensions similar to those used above. They lined the trays with plastic sheeting perforated to allow access of air to the mould.
Martinelli and Hesseltine (16) developed a new method of incubating the tempe in plastic bags with perforations at 0.25 to 1.3-cm intervals to allow access to oxygen. In this method the soybean cotyledons are inoculated with the mould and placed in the plastic bags or in plastic tubes similar to sausage casings. They can be incubated immediately or stored in a refrigerator until fermentation is desired. Then the mould overgrows the soybeans in a day or less. The plastic-bag process has been widely adopted in Indonesia and is also being used commercially in new tempe factories in the United States.
According to Shurtleff and Aoyagi (22), there are 53 tempe factories in the United States, the largest of which produces 7,000 pounds of tempe per day; the largest operation in Indonesia produces 1,760 pounds of tempe per day (20). Thus, tempe production is still a relatively small commercial operation. It offers many opportunities for new factories in countries where protein-rich meat substitutes at relatively low cost are needed by the consumers.
During tempe fermentation, not only is texture introduced into the soybean cotyledons: the proteins are partially hydrolysed; the lipids are hydrolysed to their constituent free fatty acids; stachyose, a tetrasaccharide indigestible by human beings, is reduced; riboflavin is nearly doubled; and niacin increases seven times. Also, vitamin B12, usually lacking in vegetarian foods, is synthesized by a bacterium that grows along with the essential mould (15). The bacterium has been identified as Klebsiella pneumoniae (a non-pathogenic strain) (3). Thus, tempe with its high protein content (about 40 per cent on a dry basis) can supply the consumer not only with the essential protein requirements but also with the requirements for vitamin B12
The tempe fermentation has been applied to a wide variety of bean types (5). A new type of tempe in which wheat and soybeans are combined was developed by Wang and Hesseltine (10, 31).
The tempe process is a resource of considerable potential industrial value as it can be used to introduce meat-like textures into cereal-legume substrates. It also decreases the total cooking time required for soybeans from about five or six hours to about 40 minutes boiling (30 minutes precooking and 10 minutes following fermentation). It is one of the world's first quick-cooking foods-a quality highly prized in modern food science.
Tempe has been rapidly adopted by American vegetarians and is becoming increasingly available in health-food stores and even large supermarkets in the eastern and western United States. Tempeburgers are available on the West Coast and will likely become a staple in the diet. It will probably become an accepted food in developing countries at present unfamiliar with its desirable characteristics.
A PROCESS FOR RAISING THE PROTEIN CONTENT OF HIGH-STARCH SUBSTRATES
Millions of people in the world today, particularly the poor, use cassava (manioc, yuca) as a stapte in the diet. It is an excellent source of calories but is entirely too low in protein to provide the needs of the consumer. The Indonesians centuries ago developed a fermentation process whereby the protein content of cassava or any other substrate rich in starch can be increased, improving its overall nutritive value. The product is called tape ketan when rice is the substrate and tape ketela when cassava is the substrate.
The essential micro-organisms are Amylomyces rouxli and a yeast of the Endomycoosis burtonii type (2, 14). The organisms are available in the markets of most South East Asian countries as a ragi cake. Glutinous rice is steamed, cooled, and inoculated with powdered ragi. Incubated in a warm place, the rice becomes a delicious sweet/sour alcoholic food within two or three days. The micro-organisms utilize a portion of the starch, and the protein content of the tape ketan reaches approximately 16 per cent (dry basis) - about double the initial protein content of the rice. Of considerable nutritional importance, Iysine-the first limiting amino acid in rice-is selectively synthesized, increasing about 15 per cent, and thiamine, which is very low in polished rice, increases 300 per cent, reaching a level close to that found in unpolished rice.
If cassava is the substrate, the tubers are peeled and steamed and inoculated with the powdered ragi cake. The tubers become sweetlsour and alcholic. Again a portion of the starch is utilized, and the protein content on a dry basis can reach as high as 3 per cent, or even higher if the microorganisms use a higher proportion of the starch in the tuber. The product can be sun-dried and used as an ingredient in soups.
The tape fermentation, which provides a means of raising the protein content of high starch substrates and also increases the Iysine and thiamine content of starchy substrafes, is a potentially valuable industrial resource. It should be noted that tape ketan would very likely be a highly acceptable new food in many developing countries if it were produced by small factories and distributed in an attractive preserved form.
LEAVENED BREAD-LIKE FOODS WITHOUT USE OF WHEAT OR RYE
Wheat and rye breads are staples in much of the Western world, and there has been considerable interest in developing leavened breads in countries where wheat or rye flours are unavailable. Moreover, the Indians long ago developed a process whereby leavened breads, called idli when steamed and dosai when fried, can be made from rice and black-gram dahl or other legumes. The process is a home industry. The housewife soaks rice and black-gram dahl separately during the day. In the evening she grinds them separately in a mortar and pestle; the rice is coarsely ground and the dahl finely ground for idli, and both are finely ground for dosai. She then combines them with water and a small amount of salt for seasoning to make a thick batter. This mixture is incubated overnight, during which time Leuconostoc mesenteroides grows, producing both lactic acid, which lowers the pH, and carbon dioxide, which leavens the batter. The batter is then steamed in the form of small white cakes in the morning or fried as a pancake. Idli is a type of sourdough bread. Soybeans can be substituted for the black-gram dahl. It is likely that other cereal grains and perhaps even cassava could be substituted for the rice (17, 29). Idli-like foods are low-cost and could contribute to adequate nutrition in many developing countries if they were manufactured either in the home or in small factories.
SUMMARY
The developing world is rich in indigenous food fermentations that can contribute significantly to world small-scale food processing and consumption over the next 20 to 50 years as population reaches six to eight billion. The world needs low-cost methods of providing nutritious protein rich meat analogues for its millions of consumers. The Indonesian tempe fermentation can serve as a model. A bacterium present in commercial tempe can be used to add vitamin B12 to other vegetarian foods. Fuel requirements for cooking can be decreased by applying a fungal fermentation of the tempe/ontjom type to legume substrates. The world needs high-quality meat flavours derived from vegetable protein. The soy-sauce (kecap)/miso (tauco) processes and the fishlshrimp sauce and paste processes can be modified to yield a wide variety of meat-like flavours for use in formulating new foods. The protein content of high-starch substrates can be increased by applying the Indonesian tape fermentation. Leavened sourdough bread like products can be produced without the use of wheat or rye flours, using the Indian idli-dosai fermentation process. Production of such foods by small-scale food processors will contribute both to the economy of the country and to the nutritional improvement of consumers.
REFERENCES
Summaries of the papers marked with an asterisk in the following list are included in reference 25.
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ANNOUNCEMENT: Home-Garden Research Programme
The UNU is planning to develop a research programme on indigenous tropical home-garden systems. The objective is to support projects that will gather and disseminate data on home-garden systems as a means of improving the use and management of land resources, of increasing food supply and nutrition, and of augmenting family income. Several comparative studies identifying the more effective practices from different tropical regions (South and South-East Asia, Latin America, Africa, and the Pacific islands) are planned.
Institutions interested in participating in research of this type are invited to submit a statement of interest and background to: Development Studies Division United Nations University 15-1 Shibuya 2-chome, Shibuya-ku Tokyo 150, Japan