| Applications of biotechnology to traditional fermented foods |
|I. Research priorities|
|Research Priorities in Traditional Fermented Foods|
|1 Upgrading Traditional Biotechnological Processes|
|2 Genetic Improvement of Microbial Starter Cultures|
|3 Sudan's Fermented Food Heritage|
|4 Lesser-Known Fermented Plant Foods|
|5 Lactic Acid Fermentations|
|6 Mixed-Culture Fermentations|
|III. Milk derivatives|
|7 Fermented Milks Past, Present, and Future|
|8 Lactobacillus GG Fermented Whey and Human Health|
|9 The Microbiology Ethiopian Ayib|
|10 Moroccan Traditional Fermented Dairy Products|
|11 Fermented Milk Products in Zimbabwe|
|IV. Plant derivatives|
|12 Cassava Processing in Africa|
|13 Improving the Nutritional Quality of Ogi and Gari|
|14 Solid-State Fermentation of Manioc to Increase Protein Content|
|15 Leaf and Seed Fermentations of Western Sudan|
|16 Continuous Production of Soy Sauce in a Bioreactor|
|V. Animal derivatives|
|17 Using Mixed Starter Cultures for Thai Nham|
|18 Starter Cultures in Traditional Fermented Meats|
|19 Fermented Fish Products in the Philippines|
|20 Fish-Meat Sausage|
|21 An Accelerated Process for Fish Sauce (Patis) Production|
|VI. Human health, safety, and nutrition|
|22 Nutrition and Safety Considerations|
|23 Mycotoxic Flora of Some Indigenous Fermented Foods|
|24 Commercialization of Fermented Foods in Sub-Saharan Africa|
|25 Biotechnology for Production of Fruits, Wines, and Alcohol|
|26 Future Directions|
|Board on Science and Technology for International Development|
Hamid A. Dirar
If we accept the idea that Africa is the birthplace of Man, it would seem logical that the first human or humanoid to consume a fermented food would have lived there. That fermented product could have been a piece of meat or some kind of berry picked up or stored by a hunter-gatherer. Later, and after those early men, or rather women, developed the taste for such goods they began to intentionally store fresh food items to undergo spontaneous fermentation.
Should this be the case, one would expect to find in Africa today a diverse array of fermented food products. Unfortunately, we know very little about African fermented foods because no genuine attempt has been made by any African scientist to document all the fermented foods of his or her country.
For at least one African country, the Sudan, I set out 6 years ago to collect, confirm, reconfirm, sift, and classify information on all fermented foods in the country. The major source of information was the elderly rural women of Sudan. The list of fermented foods and beverages, which now includes 60 different items, will make the basis for a book that should be ready for publication within a year. In the following sections I discuss some of the important aspects that came out of this personal initiative, which was not in any way sponsored by any agency, except perhaps some help from Band Aid of Britain.
The Sudanese seem to bring just about anything edible or barely edible to the forge of the microbe, to the extent that one could confidently say: food in Sudan is fermented. The raw materials to be fermented include the better-known products such as sorghum, millet, milk, fish, and meat. Also, a number of unorthodox raw materials are fermented: bones, hides, skins, hooves, gall bladder, fat, intestines, caterpillars, locusts, frogs, and cow urine.
The bulk of these foods is poured into the bowl of sorghum porridge' being either a sorghum (or millet) staple or its sauce and relish. The few remaining ones are alcoholic or nonalcoholic beverages, the most important of which are prepared from sorghum. In other words, every fermented food item orbits around the sorghum grain.
Sorghum fermented foods and drinks are the most sophisticated and are prepared by the most complicated procedures. Compared with similar sorghum products of Africa and indeed of the whole world, the Sudan's sorghum products stand out as unique in many respects:
· The Sudan seems to have the greatest number of fermented sorghum products. There are about 30 such products that are basically different from one another.
· There is a wide use of sorghum malt in the preparation of food and drink. Throughout Africa sorghum malt is more commonly used in the preparation of beers. In Sudan, however, while malt is used in three major beer types, it is also used to make some seven solid food products. This situation does not seem to hold true for other African countries, judging by the literature.
· The making of bread-type foods from sorghum is not common in Africa. The Sudan, however, has about 12 sorghum breads (discs, sheets, flakes). Close scrutiny of these breads reveals an influence from the Middle East; some of these breads carry names and are prepared by methods used for similar products in the Arab World.
· A comparison of the procedures followed in the preparation of some sorghum food products in Sudan with procedures for making similar products in other African countries suggests that the art of making these products traveled from Sudan to West Africa and perhaps to East Africa, too. In some cases the product travelled carrying the same Arabic-Sudanese name.
This suggests that sorghum food culture is more ancient than in other areas of Africa, and this food evidence may be taken to strengthen previous hypotheses that the origin of sorghum domestication is somewhere in northeast Africa.
The most common fermented milk product of Sudan is rob. Milk is fermented overnight, and the resulting sour milk is churned to give butter; the remaining buttermilk is rob. The principal aim behind rob production is the need to facilitate the extraction of butter from the milk. The butter (furssah) is later boiled to give butter oil or ghee, which can be stored for use in the lean season. Rob production is in the hands of animal-owning nomadic tribes, and the bulk of it is produced during the rainy season (July-October). Huge amounts of rob are thrown away during this season as useless after the butter has been removed. Some women, however, allow the souring process to proceed further after butter extraction until the curd is separated from the whey. They then collect the curd and sun dry it to give a kind of granular cheese called kush-kush that is turned into sauce for sorghum porridge in later months.
Another kind of sour milk is fermented camel milk, called gariss.
This is probably the only fermented food product invented by men. Gariss is prepared by camel boys who depend on it as their major nourishment when they roam with their herds into remote areas. The milk is fermented in a skin bag hitched to the saddle of a camel that is allowed to go about its business as usual - grazing, sleeping, walking, trotting, etc. This product, unlike rob, is fermented for consumption and no butter is removed from it.
A third indigenous dairy product is biruni, also called leben-gedim, which is a fermented unchurned milk ripened for up to 10 years! A related product, but not ripened, is mish, which is made by prolonged fermentation to the extent that maggots thrive in it. The product is consumed whole, with the maggots included. These two products are closely related to Egyptian mish (1).
Dairy products that have entered the Sudan from Egypt within the last century are jibnabeida (white cheese), zabadi (yogurt), and black cumin-flavored mish. These products are strictly confined to urban communities, where the Egyptian influence is more strongly felt.
Southeast Asia takes all the fame in the literature concerning the production of fermented fish products. But if one sorts out all the various products of that corner of the world carrying a confusing array of names, one finds that the products boil down to four major categories: sauces, pastes, dried fish, and whole salted fish. These four types of fermented fish products are also found in the Sudan, only they are all prepared from freshwater Nile fish. This situation has not been reported for other African or Arab countries. The Sudanese fish products include kejeik (large sun-dried split fish); fessiekh (salted fermented whole tiger fish); mindeshi (pounded small fish paste, fermented, and may be dried later); and terkin or meluha (fermented fish sauce or paste - not dried).
While some urban people in Sudan make very thin strips of red beef and dry them in the sun to give shermout, the traditional rural product is a truly fermented one. Thick strips of fat-bearing meat are hung on a rope indoors and left to undergo fermentation and slow drying to give a proteolytic product, shermout.
The Sudanese also ferment the sheath of fat surrounding the stomach to give the strongest-smelling product of all, miriss. Others ferment the small intestines to give musran. The clean small intestines may also first be sun dried together with strips of the lungs, heart, kidneys, liver, etc., and then all pounded together and mixed with some potash and molded into a fist-sized ball and allowed to slowly ferment and dry, to give twini-digla. The large intestine is cleaned and stuffed with fat and hung to ferment and dry for a month, to give the sausage called skin.
Beirta is prepared from he-goat meat. Small pieces of muscle meat, lungs, kidneys, liver, heart, etc., are mixed with milk and salt, packed into a clay pot, and allowed to undergo some sort of pickling, presumably.
Um-tibey is best prepared from gazelle's meat. The rumen is carefully emptied and then stuffed with the vertebrae of the neck, cut-up heart, kidneys, liver, etc. The rumen is next tied and hung high to undergo fermentation. The whole thing may then be cooked by burying it in hot ashes and embers.
Fresh bones may be fermented in a number of ways. The large bones, with pieces of attached meat and tendons, may simply be thrown on a thatched roof to ferment slowly for weeks or even months to give the product called adum (bone). The meshy ball bone endings of the ball and socket joints may be pounded fresh and fermented into a paste called dodery. The vertebrae of the backbone may be chopped into smaller pieces that are sun dried, pounded with stones, mixed with a little water and salt, molded into a ball, and allowed to ferment and dry to give kaidu-digla (bone ball).
The fresh hide, skin, or hoof may be buried in mud or moist ash to undergo fermentation. The fermented product can then be cut into strips or pieces and sun dried and stored. The gall bladder is removed full with its gall juice. Some sorghum flour or grains are added to the juice to absorb it and then hung to undergo slow drying. The product, itaga, is later pounded into a sort of spice usually consumed with fatty meat dishes.
A number of fermented vegetable products are produced in rural Sudan. Interestingly, these products can be grouped into either meat substitutes or sour milk (rob) substitutes, the two major flavors of sauces in the country. Kawal (2,3) is the major meat substitute. It is a strong-smelling product derived by fermentation of the pounded green leaves of the wild legume Cassia obtusifolia, which grows during the rainy season. The product is used in the preparation of sauces to completely replace meat or for use as a meat extender. Its protein is of high quality, rich in the sulfur amino acids. Furundu, a similar meat substitute, is prepared from the seeds of red sorrel Hibiscus sabdariffa. Sigda is another meat substitute and is prepared by fermentation of sesame oilseed presscake. All these products are dried after fermentation in the form of hard, irregular, small balls and may keep for a year or so. Other ill-defined but related products are kerjigil (from a mixture of pumpkins, sesame, and cowpea) and teshnuti (from okra seeds).
Sour milk (rob) substitutes are made from oil-bearing seeds in a manner analogous to the use of soybeans to give dairy product analogs. Rob-heb is made from the seeds of the watermelon. Rob-ful is made from peanuts. In either case the seeds are pounded into a paste that is allowed to undergo a souring fermentation. When mixed with water and turned into sauce the product has the color (off white) and taste (sour) of the sour milk sauce called mulah-rob. A related product is um-zummatah, obtained by the souring fermentation of watermelon juice. The same name is sometimes given to the sour steep water, also called mayat-aish, of fermented whole sorghum or millet grain.
Opaque beers are commonly brewed in Africa but procedures vary. The brewing of merissa in Sudan is probably the most complicated and advanced of all (4,5). The unique features of this brewing method include the use of only a small amount (5 percent) of sorghum malt as an enzyme preparation, rather than a substrate. Malt constitutes 25 to 100 percent of the substrate in the brewing of most African and European beers. Another unique feature is the use of a caramelized sorghum product, called surij, in the process. Third, there is a special starter activation step during the process that is lacking from other African brewing procedures. Also, the brewer women seem to be aware of the properties of enzymes and microbes as well as those of the acids produced during fermentation. This explains the unique treatment of the substrate, where parts of it are half cooked, others fully cooked, and yet others overcooked to meet enzyme requirements for a mixture of raw and gelatinized starch and to effect sterilization of products when needed. The merissa process has been well recognized as a complex process that deserves further investigation.
Clear beers are not common in Africa, and the literature gives reports only on otika of Nigeria and amgba of Cameroon (6,7). The Sudan has a clear sorghum (or millet) beer called assaliya (or um-bilbil). A look at the production of these three beers reveals that the assaliya process, involving some 40 steps, is far more complicated than the otika or amgba procedures, which involve fewer than 20 steps. It is suggested that the art of brewing clear beers traveled to West Africa from Sudan. Amgba of Cameroon is even called bilbil.
In Sudan there are perhaps 30 to 50 opaque beer types with different but related brewing methods. The area seems to be a center of diversity of sorghum beers, and perhaps the art of brewing of opaque beers traveled to East Africa from this region.
The traditional wines of Sudan are the date wines. The palm wine of West Africa is not known in Sudan - nor is lagmi, the wine obtained by fermentation of the sap of the date palm as practiced in northwest Africa. Only the fruit of the date palm is fermented in the Sudan, and the bulk of wines thus made are produced and consumed in the Northern Province where most of the date palms exist. At least 10 different date wines are produced, the most important of which are sherbot, nebit, and dakkai (8).
In the Southern Sudan a kind of mead is produced by fermentation of diluted wild bee's honey. The product, called duma, is primed by a specially prepared starter culture called duma-grains (iyal-duma).
FERMENTED FOODS AND SURVIVAL STRATEGIES
A careful examination of fermented food products of Sudan would immediately suggest a close link between food fermentation and food shortage in this part of the world. First, about 80 percent of these foods, particularly the marginal ones using bones, intestines, fat, etc., are found in western Sudan in the Kordofan and Darfur regions, the traditional famine areas. Second, most of the foods are preserved by both fermentation and drying, which means that they are intended for long storage and that food shortages or even famine are anticipated. In other words, the inventors of such foods have the experience of repeated famines.
Further, practically all fermented sauce ingredients are produced during the late months of the rainy season, which shows that, unless a person secures all of his or her food requirements from this short season, he or she will probably suffer greatly in the remaining 9 months of the year. The harsh environment has actually dictated the need to ferment and dry anything that might prevent starvation. To live on the edge of the desert must have been a great force in sharpening the sense for survival and creativity.
The strong link between many fermented foods and food shortages is also revealed by the fact that if a family became rich it would drop a number of fermented foods from its menu, not because of social pressure but because there was no longer any need for them now that ample supplies of meat, milk, poultry, etc., were available. Poor people who ferment bones, hides, locusts, etc., do so not because they relish these foods but because it is part of the coping strategy they follow to deal with the vagaries of a capricious environment.
The first victims of any famine are the children, among whom death exacts a great toll. Babies and children die in the laps of women more than they do in the laps of men. Maternal compassion must be the greatest impetus behind the rural woman's desperate attempts to save her child that propel her to look for an insect, a piece of hide, a frog, or a bone as savior. Many fermented foods are thus famine foods, and rural women must be credited with their invention. These women must have saved thousands of children from certain death during famines. Their vital role must be recognized and hailed.
BIOTECHNOLOGY AND FERMENTED FOODS
This relationship has not been discussed widely in the literature. One can imagine, however, that biotechnology can be of help in the improvement of fermented foods at three levels:
· Raw materials. Fermented foods are produced from either animal or plant starting materials, and the availability of these substrates will of course aid in the production of fermented foods. Biotechnological methods to improve animal and plant production have been dealt with by experts in those fields on many occasions.
Only a special reminder should be made not to neglect certain wild plants and marginalized crops - the so-called lost crops of Africa (e.g., sorrel and okra). Attempts to restore the forest cover should give some attention to trees that bear fruits used during famines or even trees that host caterpillars.
· Fermentation engineering. Recent developments in biotechnology have given rise to great innovations in bioreactor designs. Most of these designs deal with liquid reaction media, but it should not be forgotten that a great number of fermented foods are produced through a solid-substrate fermentation in which the fermenting paste is frequently hand mixed. Bioreactors to simulate such a process are needed for the modernization of such traditional fermented foods.
· Microbiology and enzymology. There are many opportunities for biotechnological innovations in the microbiology of fermented foods.
First, all the microorganisms involved should be isolated, characterized, and preserved as a germplasm collection. Second, the metabolic role of each of the strains involved should be clearly identified, and their full potential, even in other fields of biotechnology, should be studied. The powerful technique of monoclonal antibodies for the characterization of different strains of the same species can be of great help in this area.
Many of these organisms have the enzyme complement to produce vitamins and amino acids in fermented foods. This potential can be improved through the technique of recombinant DNA technology to produce strains that are capable of producing and releasing the required amino acid or vitamin into the food.
To avoid food losses due to spoilage-causing organisms and to avoid possible development of food-poisoning microbes, it is possible to genetically engineer a strain required for a process as a pure culture. Such a strain may bring about all the changes required in the food and grow at a convenient temperature.
1. Abdel-Malek, Y. 1978. Traditional Egyptian dairy fermentations. Global Impacts of Applied Microbiology 5:198-208.
2. Dirar, H. A. 1984. Kawal, a meat substitute from fermented Cassia obtusifolia leaves. Economic Botany 38:342-349.
3. Dirar, H. A., D. B. Harper, and M. A. Collins. 1985. Biochemical and microbiological studies on kawal, a meat substitute derived by fermentation of Cassia obtusifolia leaves. Journal of the Science of Food and Agriculture 36:881-892.
4. Dirar, H. A. 1976. The art and science of merissa fermentation. Sudan Notes and Records 57:115-129.
5. Dirar, H. A. 1978. A microbiological study of Sudanese merissa brewing. Journal of Food Science 43:1683-1686.
6. Ogundiwin, J. O. 1977. Brewing otika ale from guinea corn in Nigeria. Brewing and Distilling International 7(6):40-41.
7. Chevassus-Agnes, S., J. C. Favier, and A. Joseph. 1976. Technologie traditionelle et valeur nutritive des "bieres" do sorgho du Cameroon. Cahier de Nutrition et de Dietetique 11(2):89-104.
8. Ali, M. Z., and H. A. Dirar. 1984. A microbiological study of Sudanese date wines. Journal of Food Science 49:459-460, 467.