Fermented cereals a global perspective. Chapter 2.

Africa is one of the lowest producers of cereals globally (Table 1). Major cereals grown in Africa include maize, rice, sorghum and millet (Table 1). Cereals are more widely utilized as food in African countries, than in the developed world. In fact, cereals account for as much as 77 % of total caloric consumption in African countries (Mitchell and Ingro, 1993), and contribute substantially to dietary protein intake in a number of these countries. A majority of traditional cereal-based foods consumed in Africa are processed by natural fermentation. Fermented cereals are particularly important as weaning foods for infants and as dietary staples for adults.

This Chapter reviews the production of a number of traditionally fermented cereals in African countries.

		1997	% of world production
Maize	24,798			4.2
Millet	10,950			38.9
Rice	11,321			2.0
Sorghum	17,400			28.2
Wheat	3,140			0.5

Fermented cereal-based food products produced in African countries can be classified on the basis of either the raw cereal ingredients used in their preparation, or the texture of the fermented product.

a) wheat-based foods e.g. bouza, kishk
b) rice-based foods e.g. busa
c) maize-based foods e.g. ogi, bread, kenkey
d) millet based foods e.g. kunuzaki
e) sorghum based foods e.g. pito, ogi, bogobe, kisra, burukutu, kisra, injera
f) barley based foods e.g. beer

a) liquid (gruel) e.g. ogi, mahewu, burukutu, pito, uji
b) solid (dough) and dumplings e.g. kenkey, agidi
c) dry (bread) e.g. kisra, injera

Pre-fermentation processing of cereals is largely dependent on the end product desired. In most cases, grains are sun-dried prior to fermentation. Treatments such as washing, steeping, milling and sieving are pre-fermentation processing steps applied in the preparation of fermented gruels, while milling and sieving are required as pre-fermentation processing steps in the production of dry fermented foods such as bread.

Indigenous fermented foods prepared from major cereals are common in many parts of Africa. Some are used as beverages and breakfasts or snack foods while a few are consumed as staples and weaning foods (Tables 2 and 3).

Ogi is a porridge prepared from fermented maize, sorghum or millet in West Africa. It is a staple of that region, and serves as a weaning food for infants. The traditional preparation of ogi (Fig.1) involves soaking of corn kernels in water for 1 to 3 days followed by wet milling and sieving to remove bran, hulls and germ (Odunfa 1985; Akinrele 1970). The pomace is retained on the sieve and later discarded as animal feed while the filtrate is fermented (for 2-3 days) to yield ogi, which is a sour, white starchy sediment. Ogi is often marketed as a wet cake wrapped in leaves or transparent polythene bags. It is diluted to a solids content of 8 to 10% and boiled into a pap, or cooked and turned into a stiff gel called "agidi" of "eko" prior to consumption.

Microbiological and nutritional studies by Akimrele (1970) showed that the lactic acid bacterium Lactobacillus plantarum, the aerobic bacteria Corynebacterium and Aerobacter, the yeasts Candida mycoderma, Saccharomyces cerevisiae and Rhodotorula and molds Cephalosporium, Fusarium, Aspergillus and Penicillium are the major organisms responsible for the fermentation and nutritional improvement of ogi. Odunfa (1985), determined that L. plantarum was the predominant organism in the fermentation responsible for lactic acid production. Corynebacterium hydrolysed corn starch to organic acids while S. cereviseae and Candida mycoderma contributed to flavour development.

Substantial nutrient losses occur during the various steps of ogi processing. According to Lagunna and Carpenter (1951), steeping, milling and sieving are the processing steps during which considerable nutrient losses take place. Much of the protein in cereal grains is located in the testa and germ which are usually sifted off during processing. These losses have been evaluated and reported by several workers (Hamad and Fields, 1979; Oke, 1967).

Product name	Area of production	Substrate	Microorganisms involved	Textural characteristics of product
Ogi BogobeKoko and kenkey Mawe Mahewu (magou) Uji Kisra Enjara	Nigeria, Benin BotswanaGhana Dahomey South Africa East Africa Sudan Ethiopia	Maize, sorghum or millet SorghumMaize, sorghum or millet Maize Maize sorghum or millet Maize, sorghum or milletSorghum Sorghum	Lactobacillus sp. and yeasts UnknownLactobacillus sp. and yeastsL. fermentum, L. cellobiosis, L. brevis, yeasts – Candida Krusei and S. cerevisaeL. delbrueckii, and L. bulgaricusLactobacillus sp.Unknown Candida guilliermondii	Soft or stiff gel PorridgeDough Dough Liquid Liquid Dough Dough

Efforts are currently underway in Africa to modify the processing of ogi with a view to enhancing its nutritive value, shelf-life and possible therapeutic qualities. A protein-enriched ogi containing 10% soya flour was developed by the Federal Institute of Industrial Research (FIIRO), Oshodi, Lagos, Nigeria (Akinrele, 1970; Akinrele et al., 1970). In Nigeria, Olukoya et al. (1994) reported the development of an ogi product (dogik) having therapeutic properties on the basis of its ability to control diarrhoea among infants. This finding is of great relevance since ogi is used as a popular weaning food for children in African countries.

Odunfa et al. (1994) investigated the possibility of improving the limiting lysine level in ogi. Fifty mutants from L. plantarum and seven mutants from a yeast strain were selected from thialysine-resistant cultures capable of overproducing lysine, and analysed for lysine production. Up to a 12-fold increase in lysine production was observed for L. plantarum and a 3 – 4 fold increase for yeasts was observed. Utilisation of the mutants as starter cultures resulted in a three-fold increase in the lysine content of ogi. The use of high lysine corn for improving the nutritional value of ogi was reported by Banigo et al. (1974) and Adeniji and Potter (1978).

Dehydration of ogi by drum or tray-drying has been shown to prolong its shelf-life (Plahar and Leung, 1983). Drum drying was however reported to destroy heat-sensitive nutrients in ogi (Labuza, 1972). Adeniji and Potter (1978) reported an appreciable loss in the available lysine content of ogi as a result of drum drying.

Recent studies have sought to optimize the role of Lactobacillus species in the safety of fermented foods. Olasupo et al. (1995) determined bacteriocin-producing Lactobacillus isolates to be active against common food-borne pathogens including Salmonella. This bacteriocin also improved the shelf-life of ‘jellied’ ogi, extending it by 10 days (Olasupo et al. 1997).

Banku is a popular staple consumed in Ghana. It is prepared from maize and/or from a mixture of maize and cassava (Owusu-Ansah et al. 1980). Preparation procedures for banku are summarized in Fig. 2. The preparation of banku involves steeping the raw material (maize or a mixture of maize and cassava) in water for 24 hrs followed by wet milling and fermentation for 3 days. The dough is then mixed with water at a ratio of 4 parts dough to 2 parts water; or 4 parts dough to 1 part cassava and 2 parts water. Continuous stirring and kneading of the fermented dough is required to attain an appropriate consistency during subsequent cooking. Microbiological studies of the fermentation process revealed that the predominant microorganisms involved were lactic acid bacteria and moulds (Beuchat, 1983). The development of a quick-cooking fermented ‘banku’ using a drum-drying process was reported by Owusu Ansah et al. 1988.

This is a fermented maize dough which is popularly consumed in Ghana. During the production of kenkey, the dough is divided into two parts: one part, the ‘aflata’ is cooked into a thick porridge, while the other uncooked part is later mixed with the ‘aflata’. The resulting mixture is moulded into balls and wrapped in dried maize husk or plantain leaves, after which it is steamed. It is interesting to note that kenkey varieties vary widely throughout Ghana. In northern Ghana, sorghum is sometimes used instead of maize for preparation of the dough.

Microbiological studies of kenkey production by Jespersen et al. (1974) highlighted the significance of yeasts and moulds in the production of the fermented maize dough. A mixed flora consisting of Candida, Saccharomyces, Penicillium, Aspergillus and Furasium species were found to be the dominant organisms during the preparation of this food product. Halm et al. (1993) concluded that a homogenous group of obligatively heterofermentative lactobacilli related to L. fermentum and L. reuteri play a dominating role during kenkey production.

This is a fermented maize meal commonly consumed as a staple among black South Africans. It is traditionally prepared by adding one part of maize meal to 9 parts of boiling water. The suspension is cooked for 10 minutes, allowed to cool and then transferred to a fermentation container. At this stage, wheat flour (about 5% of the maize meal used) is added to serve as a source of inoculum. Fermentation occurs in a warm sunny place within 24 hrs. Streptococcus lactis is the main fermenting organism in traditionally prepared mahewu (Hesseltine, 1979).

Mahewu is known to offer some advantages over ogi in that the initial wild fermentation by fungi, etc. is eliminated by boiling both the maize meal and water for steeping. Furthermore, it is pre-cooked and requires only mixing prior to consumption. Mahewu consists of coarse maize particles while ogi contains very fine pasty maize particles.

Mahewu is currently produced on an industrial scale (Fig. 4) as a dry food product which is marketed as a pre-cooked ready-mix powder. The industrial production of mahewu therefore spurs the need for the development of starter cultures. Schwigart & Fellingham (1963) evaluated the use of various lactic acid bacteria as starters in mahewu fermentation and determined that Lactobacillus delbruckii and Lactobacillus bulgaricus produced the most acceptable mahewu at a temperature of 50⁰ C, which was determined to disallow the growth of unwanted microorganisms. Van Noort and Spence (1976) of Jabula Foods Limited, South Africa produced a more acceptable mahewu product at room temperature using a combination of starters including an acid-producing bacterium, a yeast and a non-acid producing bacterium. The identity of the various organisms used was not however disclosed by these workers.

Mawe is a sour dough prepared from partially dehulled maize meal which has undergone natural fermentation for a one to three-day period. Studies on mawe production were conducted by Houhonigan (1994). An estimated 14-16% of total maize production in Cotonou, Benin is used for mawe production. Quantitatively mawe is less important than ogi, but is suitable as a basis for the preparation of many dishes, including those prepared from ogi (Fig. 5). Mawe is produced using both a traditional (home) process (Fig. 6) and a commercial (Fig. 7) process. The commercial process for mawe production was developed to meet quality requirements of urban mawe consumers (Hounhouigan, 1994).

Traditional mawe production involves cleaning maize by winnowing, washing in water and crushing in a plate disc mill. The crushed maize is screened by sieving whereby grits and hulls are separated by gravity and the fine endosperm fraction collected in a bowl.

The grits are not washed but home dehulled, following which they are mixed with the fine fraction, moistened over a 2 to 4-hour period and milled to a dough. The kneaded dough is then covered with a polyethylene sheet and allowed to ferment naturally to a sour dough in a fermentation bowl, or wrapped in paper or polyethylene. In the commercial process which takes place entirely in a milling shop, the grits are washed by rubbing in water, following which the germ and remaining hulls are floated off and discarded along with the water. The sedimented endosperm grits are subsequently blended with the fine endosperm fraction.

The main difference between between the traditional and the commercial process of mawe production is that hulls and germs are removed during the commercial processing of mawe. Commercial mawe is whiter in appearance than home-produced mawe and has better swelling and thickening characteristics, but is of lower nutritional value. A compositional study of mawe resulting from both the traditional and commercial processes showed that average moisture contents varied between 45 and 47 % and did not differ significantly. The titratable acidity of home-made and commercial mawe samples was similar (1.2 – 1.4% w/w as lactic acid), but home-made mawe was of a slightly higher pH (Table 4). The crude protein, crude fat, crude fibre and ash contents of home-made mawe were higher than those of commercial mawe since more hulls and germs were retained during home production (Hounhouigan et al., 1993).

Dominant microorganisms in mawe preparation include lactic acid bacteria (mainly Lactobacillus fermentum and its biotype L. cellobiosis, L. brevis) and yeasts (Candida krusei and Saccharomyces cerevisiae (Table 3).

On the basis of production procedures three types of injera are distiguishable: (i) thin injera which results from mixing a portion of fermented sorghum paste with three parts of water and boiling to yield a product known as ‘absit’’ which is, in turn, mixed with a portion of the original fermented flour (ii) thick injera, which is reddish in color with a sweet taste, is a ‘tef’ paste that has undergone only minimal fermentation for 12-24 hours; (iii) komtata-type injera, which is produced from over-fermented paste, and has a sour taste. The paste is baked or grilled to give a bread-like product. Yeasts are the major microorganisms involved in the fermentation of the sweet type of injera (Beuchat, 1983).

The comparative chemical composition of injera prepared from different cereals (Gebrekidan and Babrettwat, 1982) is shown in Table 5. There is little variation in the nutrient composition of injera prepared from different cereals, which indicates the potential for the use of cereals other than sorghum in the production of injera.

This is a thin pancake-like leavened bread prepared from whole sorghum flour. It is a dietary staple in Sudan. This fermented sorghum bread has a very sour taste (Ejeta, 1982). It is prepared by mixing sorghum flour with water to give a thick paste which is allowed to ferment for 12-24 hours, following which the paste is thinned to a desirable consistency with water just prior to baking (Fig. 9).

Ejeta (1982), conducted an evaluation of the effect of sorghum variety on kisra quality. Cultivars with a white chalky pericarp and without a subcoat were judged to have the best sensory properties. El-Tinay et al., (1979), reported that there was a slight increase in protein and fiber and an appreciable decrease in carbohydrate (starch and sugars) during the fermentation of kisra. An amino acid analysis of kisra prepared from three different cultivars of sorghum indicated slight differences in the levels of the various amino acids (Table 6).

Kishk is a fermented product prepared from parboiled wheat and milk (Fig. 10). It is consumed in Egypt and in most Arabian countries (Morcos et al., 1973a). During the preparation of kishk, wheat grains are boiled until soft, dried, milled and sieved in order to remove the bran. Milk is separately soured in earthenware containers, concentrated and mixed with the moistened wheat flour thus prepared, resulting in the preparation of a paste called a hamma. The hamma is allowed to ferment for about 24 hrs, following which it is kneaded and two volumes of soured salted milk are added prior to dilution with water. Alternatively, milk is added to the hamma and fermentation is allowed to proceed for a further 24 hours. The mass is thoroughly mixed, formed into balls and dried.

Kishk is a highly nutritious food, having a protein content of about 23.5%. It is of a high digestibility, and high biological value. Microorganisms responsible for fermentation include Lactobacillus plantarum, L. brevis, L. casei, Bacillus subtilis and yeasts (Beuchat, 1983; Odunfa 1985). Kishk is usually over-heated to improve its keeping quality.

Bogobe is a sorghum porridge prepared in Botswana from fermented and non-fermented sorghum (Figure 11). Fermented bogobe is a soft porridge, known as ting while the non-fermented bogobe is a thick porridge called monokwane (Boising and Nancy, 1982). Information relevant to microorganisms involved in the ferementation of bogobe, and the nutritional changes which occur during fermentation is still scanty.

Table 6: Essential amino acid profiles for flour, fermented dough, and kisra produced from Three Sorghum Cultivars*

This is a millet-based non-alcoholic fermented beverage widely consumed in the Northern parts of Nigeria. This beverage is however becoming more widely consumed in southern Nigeria, owing to its refreshing qualities. Adeyemi & Umar (1994), described the traditional process for the manufacture of kunu-zaki. This process involves the steeping of millet grains, wet milling with spices (ginger, cloves, pepper), wet sieving and partial gelatinization of the slurry, followed by the addition of sugar, and bottling (Figure 12). The fermentation which occurs briefly during steeping of the grains in water over a 8-48 hr period is known to involve mainly lactic acid bacteria and yeasts.

Sopade and Kassum (1992) highlighted the significance of rheological characteristics in processing, quality control, sensory evaluation and structural analysis of kunu-zaki. Increasing temperatures reduced viscosity but did not alter the rheological characteristics of the product. The time of shear (up to 1 hr) did not appreciably alter the viscosity.

Storage studies conducted by Adeyemi and Umar (1994) revealed that the product had a shelf-life of about 24 hrs at ambient temperature, which was extended to 8 days by pasteurization at 60⁰ C for 1 hr and storage under refrigeration conditions. Studies are currently underway at the Federal Institute of Industrial Research Oshodi (FIIRO) Lagos, Nigeria to produce kunun-zaki of improved shelflife. FIIRO has been able to preserve kunun-zaki effectively for 90 days, with the use of chemical preservatives.

This is a popular alcoholic beverage of a vinegar-like flavour, consumed in the Northern Guinea savanna region of Nigeria, in the Republic of Benin and in Ghana. The preparation of burukutu involves steeping sorghum grains in water overnight, following which excess water is drained. The grains are then spread out on to a mat or tray, covered with banana leaves and allowed to germinate. During the germination process, the grains are watered on alternate days and turned over at intervals. Germination continues for 4-5 days until the plumule attains a certain length. The malted grains are spread out in the sun to dry for 1-2 days, following which the dried malt is ground into a powder. Gari, (a farinaceous fermented cassava product) is added to a mixture of the ground malt and water in a ratio of one part gari to two parts malt and six parts water. The resulting mixture is allowed to ferment for 2 days, following which it is boiled for approximately 4 hrs and allowed to mature for a further 2 days. The resulting product is a cloudy alcoholic beverage.

Sorghum malt contains primarily yeasts and moulds as the indigenous microflora. Microorganisms associated with the fermentation include yeasts mainly Saccharomyces cerevisiae and S. chavelieri and the bacteria, Leuconostoc meseteroides.

The pH of the fermenting mixture decreases from about 6.4 to 4.2 within 24 hrs of fermentation and decreases further to 3.7 after 48 hrs. At the termination of the 2-day maturing period Acetobacter sp. and Candida sp. (Faparusi et al., 1973) are the dominant microorganisms. Boiling prior to maturation eliminates lactics and other yeasts. Fully matured burukutu beer has an acetic acid content which varies between 0.4 and 0.6%.

Pito is the traditional beverage drink of the Binis in the mid-western part of Nigeria. It is now very popularly consumed throughout Nigeria owing to its refreshing nature and low price. Pito is also widely consumed in Ghana. The preparation of pito involves soaking cereal grains (maize, sorghum or a combination of both) in water for 2 days, followed by malting, and allowing them to sit for 5 days in baskets lined with moistened banana leaves. The malted grains are ground, mixed with water and boiled. The resulting mash is allowed to cool and later filtered through a fine mesh basket. The filtrate thus obtained is allowed to stand overnight, or until it assumes a slightly sour flavour, following which it is boiled to a concentrate. A starter from the previous brew is added to the cooled concentrate which is again allowed to ferment overnight. Pito, the product thus obtained, is a dark brown liquid which varies in taste from sweet to bitter. It contains lactic acid, sugars, amino acids and has an alcohol content of 3% (Ekundayo,1969). Organisms responsible for souring include Geotrichum candidum and Lactobacillus sp. while Candida sp. are responsible for the alcoholic fermentation.

This is an alcoholic drink which is widely consumed in Sudan. It is prepared from sorghum and millet by a relatively complex process. Brewing takes place in three distinct phases (i) ‘ajeen’ fermentation, a lactic souring of sorghum, (ii) ‘debosa’ fermentation, a starter activating phase and (iii) merissa fermentation, an alcoholic fermentation.

The fermentation of merissa is similar to that applied in the preparation of other African alcoholic beverages. Ajeen fermentation is accomplished by lactic acid and acetic acid bacteria and yeasts at a pH of about 4.0, an alcoholic content of 1% and lactic acid content of 2.5%. At the final stage of merissa fermentation, however, the alcoholic content increases to about 6 %.

Bouza, a fermented alcoholic beverage produced from wheat in Egypt, has been known by the Egyptians since the days of the Pharaohs (Morcos et al., 1973). It is a thick, pasty yellow beverage with an agreeable taste and produces a sensation of heat when consumed. It is prepared by coarsely grinding wheat grains, placing a portion of them (3/4) in a wooden basin and kneading them with water into a dough. The dough is cut into thick loaves which are very lightly baked. Meanwhile, the remainder of the grains (approximately ¼ of the total amount of wheat grains) is moistened with water, germinated for 3-5 days, sun-dried, ground and mixed with the loaves of bread which are soaked in water in a wooden barrel. Bouza from a previous brew is added to serve as an inoculum. The mixture is allowed to ferment at room temperature for a 24-hour period, following which the product is sieved to remove large particles and diluted with water to a desired consistency.

Like other opaque beers, bouza has a very short shelf-life and is expected to be consumed within a day. Its pH increases to between 3.9 and 4.0 and its alcoholic content to between 3.8-4.2% within a 24-hour period.

	Akassa (Makume, a gelatinized dough)
	Ablo (Steamed-cooked bread)
	Akpan (Pre-gelatinized yogurt-like product)
MAWE	Massa (Fritter)
	Paté (Fritter)
	Yeke-yeke (Couscous)
	Aklui (Granulated porridge)
	Koko (Porridge)

Nutrient	Sorghum	Tef	Corn	Finger Millet	Barley	Wheat
Energy (cal)	193	162	185	172	167	172
Moisture (%)	52.0	59.8	54.0	56.1	58.0	57.4
Protein (g)	7.1	4.2	5.0	3.8	3.5	5.4
Fat (g)	0.6	0.6	0.7	0.3	0.3	0.9
Carbohydrates (g)	39.8	33.9	39.6	38.4	37.5	35.6
Fiber (g)	0.9	1.7	0.7	4.0	0.9	0.9
Ash (g)	0.5	1.5	0.7	1.4	0.7	0.7
Calcium (mg)	10	64	27	169	16	28
Phosphorus (mg)	111	129	120	103	128	155
Iron (mg)	3.5	30.5	2.1	17.3	4.2	3.3
ß-Carotene equiv. (ug)	0	0	Trace	Trace	0	0
Thiamin (mg)	0.17	0.21	0.14	0.14	0.12	0.14
Riboflavin (mg)	0.08	0.07	0.06	0.01	0.05	0.09
Niacin (mg)	1.7	0.8	0.7	0.2	3.0	2.4
Ascorbic acid (mg)	0	1	2	1	0	1

Wheat grains covered with water
Heat slowly to boiling and simmer until soft
Wash with cold water	Sour milk by churning in skin bags
Dry on mats	Concentrate
Grind
Remove seed coats by sieving
Place in pots and moisten with lightly salted boiling water	Mix to form a paste
	Ferment for 24 h
	Mix and add whey
	Dilute with milk or water to give a syrupy consistency
	Ferment for 24 h
	Mix and form into small balls
	Place on mats and sun dry
	KISHK

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