CHAPTER 2 CEREAL FERMENTATIONS IN AFRICAN COUNTRIES

INTRODUCTION

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.

Table 1. Production of Cereals (Thousand Metric Tons) in Sub-Saharan Africa

		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

Source: FAO 1997

CLASSIFICATION OF FERMENTED CEREALS

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.

Classification on the basis of raw cereal ingredients:

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

Classification on the basis of texture:

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

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.

FERMENTED CEREAL-BASED FOODS

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). 

Fermented Gruels and Non-Alcoholic Beverages

Ogi

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).

Table 2. Fermented Non-Alcoholic Cereal-Based Foods In Africa

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 UnknownLactobacillussp. and yeastsL. fermentum, L. cellobiosis, L. brevis, yeasts – Candida Krusei and S. cerevisaeL. delbrueckii, and L. bulgaricusLactobacillussp.Unknown Candida guilliermondii	Soft or stiff gel PorridgeDough Dough Liquid Liquid Dough Dough

Table 3: Alcoholic beverages produced from cereals in Africa 

Product name	Area of Production	Substrate	Starter	Mestrum
Burukutu PitoKaffir beer Busaa (maize beer) Malawa beer Zambian opaquemaize beer Merissa Seketeh Bouza Talla Kishk	Ethiopia Nigeria (north) Northern Ghana Nigeria (Bendel) Ghana South Africa East Africa Uganda Zambia Sudan Nigeria (south) Egypt Ethiopia Egypt	Guinea corn and cassava Guinea corn and maize Kaffir corn (or maize) Maize Maize Maize Sorghum Sorghum Maize Wheat or maize Sorghum Wheat and milk	Yeasts and lactic acid bacteria Moulds, yeast and Lactobacillus sp. Lactobacillus spp. and yeasts Yeasts and Lactobacillus spp. Candida krusei Yeasts Lactic acid bacteria, acetic acid bacteria Unknown Unknown Unknown Lactobacillus spp., yeasts and Bacillusspp.	Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid

Corn

 

Cleanfor 2 to 3 days

 

Wet mill

 

Sieve and discard pomace

Ferment filtrate and allow to sediment

 

for 1-3 days

 

OGI

Figure 1: Flow diagram for the preparation of ogi.

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

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. 

Kenkey

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.

Corn

 

Clean

Steep for 24 hr

Wet mill

Ferment for 3 days

Dough formation

Stir and knead

Cook

BANKU

Fig. 2 : Flow diagram for the preparation of Banku

Maize

Clean

Steep (24-48 hrs)

Mill

Dough formation

Ferment for 72 hr

Cooked dough                             Raw dough 

Mix (Aflatasation)

Mould into balls

Wrap with maize husks

Boil for about 3 hrs

KENKEY

Fig. 3: Flow chart for the traditional preparation of kenkey

Mahewu

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

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. 

Maize meal

Mix in warm water to give 8% solids content

Cook at 121^oC for 15 minutes

Cool

Inoculate

(5% wheat flour or an adapted pure culture of Lactobacillus delbrueckii)

Incubate at 30-50^oC for wheat innoculum, or at 45^oC for L. delbrueckii innoculum 

Ferment for 36 hrs with mixing only at the beginning of fermentation

Heat for 10-15 mins under pressure (7 psi)

Spray or drum dry

MAHEWU

Fig. 4: Industrial preparation of mahewu

	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)

Fig. 5: Main dishes prepared from mawe

Maize grains

Clean and wash

Crush

Screen and dehull; discard hull

Soak in water for 2-4 h and drain

Grind

Knead to form a dough

Ferment for 1-3 days

HOME-PRODUCED MAWE

Fig. 6: Flow diagram of the home process of mawe production

Maize grains

Clean and wash

Crush

Screen and dehull

Soak and wash; discard hull, and germ

Drain

Add water and allow to stand for 2-4 h

Grind

Add water and knead to form a dough

Ferment for 1-3 days

COMMERCIAL MAWE

Fig. 7: Flow diagram for the commercial production of mawe

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).

Table 4: Chemical Characteristics of Mawe 

	Homez Produced Mawe	Commercially Produced Mawe
	(collected from homes) n = 20	(fresh from mill) n = 15	(sold at the market) n = 15
pH Titratable acidity (% w/w, as lactic acid) Moisture content (%) Crude protein (% dwb) Crude fat (% dwb) Crude fibre (% dwb) Ash (% dwb) Soluble carbohydrate (% dwb)	4.2 1.2 46.8 9.2 2.3 0.7 1.1 86.7	3.9 1.1 45.9 8.3 0.9 0.4 0.6 89.8	3.8 1.4 45.1 8.2 1.0 0.4 0.6 89.8

Bread and Pancakes

Injera

Injera is the most popular baked product in Ethiopia. It is a fermented sorghum bread with a very sour taste (Stewart and Getachew, 1962) and is the undisputed national bread of Ethiopia. The baked product is referred to by different names depending on the locality of production in Ethiopia. It is referred to as ‘bidena"in Oromigua, ‘taeta’ in Giragigua, and ‘solo’ in Walaytigna. According to a report by Gebrekidan and Gebrettiwat (1982) over 8% of total sorghum production in Ethiopia is used for ‘injera production. The sorghum grains are dehulled manually or mechanically and milled to flour which is subsequently used in the preparation of injera (Figure 8).

Sorghum flour

Mix with water, 4:1 w/v

Knead to form a dough

Mix with starter

(Fermented yellowish liquid saved from previously fermented dough)

Knead 

Add water 

Ferment for 48 h

Add water and allow to stand for 1 h

Bake on hot

greased clay griddle metal till holes begin to form on top

 

INJERA

Fig. 8: Flow diagram for the preparation of injera

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. 

Kisra

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).

Table 5: Nutritional Composition of Injera (per 100g.). Prepared from Different Cereals

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

* Source: Gebrekidam & Gebrelfiwat (1982)

Sorghum flour

Mix with water (60:40 w/v)

Ferment for 12 – 24h

Add water to form a thin slurry

Bake on hot oiled panKISRA

Fig. 9: Flow diagram for the preparation of kisra

Kishk

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

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*

Note: Dough fermented at 28°C for 18 h at pH 3.7.

* Source: El-Tinay et al. (1979)

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 togive a syrupy consistency
	Ferment for 24 h
	Mix and form into small balls
	Place on mats and sun dry
	KISHK

Fig. 10: Flow diagram for the preparation of kishk

Sorghum grains

Wash with water

Dehull (mechanical or manual)

Discard bran and grind to a coarse meal

Add Lukewarm water (1:1 w/v) to form a slurry

Allow to ferment in a closed environment for 24 h

Cook in boiling water for 12 – 15 min.

BOGOBE

Fig. 11: Flow diagram for the preparation of bogobe from sorghum

Alcoholic Beverages

Kunu-Zaki

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.

Dehulled millet grains

Clean

Steep

Wet mill with the addition of spices

Wet-sieve

Allow to settle

Decant supernatant and retain slurry

Slurry in cold water + Slurry in boiling water

Add sweetener and mix

Bottle

KUNU-ZAKI

Fig. 12: Flow Chart for the Traditional Process of Kunu-zaki

Burukutu

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

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. 

Merissa

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

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.

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FERMENTED CEREALS

Animal or plant tissues subjected to the action of microorganisms and/or enzymes to give desirable biochemical changes and significant modification of food quality are referred to as fermented foods (Campbell-Platt 1994). Fermentation is the oldest known form of food biotechnology; records of barley conversion to beer date back more than 5000 years (Borgstrom 1968). According to Steinkraus (1995), the traditional fermentation of foods serves several functions:

"1. Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates

  2. Preservation of substantial amounts of food through lactic acid, alcoholic, acetic acid, and alkaline fermentations

  3. Enrichment of food substrates biologically with protein, essential amino acids, essential fatty acids, and vitamins

  4. Detoxification during food fermentation processing

  5. A decrease in cooking times and fuel requirements"

Aside from alcoholic fermentations and the production of yogurt and leavened bread, food fermentations continue to be important primarily in developing countries where the lack of resources limits the use of techniques such as vitamin enrichment of foods, and the use of energy and capital intensive processes for food preservation. The technology of producing many indigenous fermented foods from cereals remains a household art in these countries (Chaven and Kadam 1989). Prospects for applying advanced technologies to indigenous fermented foods (Wood 1994) and for the production of value-added additive products, such as colors, flavors, enzymes, antimicrobials, and health products (Cook 1994) during food fermentations have been reviewed. 

Special mention should be made of the microbiological risk factors associated with fermented foods. The safety of fermented foods has been recently reviewed (Nout 1994). Cases of food-born infection, and intoxications due to microbial metabolites such as mycotoxins, ethyl carbamate, and biogenic amines have been reported in fermented foods. Major risk factors include the use of contaminated raw materials, lack of pasteurization, and use of poorly controlled fermentation conditions. On the other hand, non-toxigenic microorganisms can serve to antagonize pathogenic microorganisms and even degrade toxic substances such as mycotoxins (Nakazato et al. 1990) in fermented foods. 

Indigenous Fermented Cereal Foods

Most bacterial fermentations produce lactic acids; while yeast fermentation results in alcohol production. Many of the indigenous fermentation products of cereals are valued for the taste and aroma active components produced and are used as seasonings and condiments. A summary of flavor compounds formed in such products was compiled by Chaven and Kadam (1989). A number of fermented products utilize cereals in combination with legumes, thus improving the overall protein quality of the fermented product. Cereals are deficient in lysine, but are rich in cystine and methionine. Legumes on the other hand are rich in lysine but deficient in sulfur containing amino acids. Thus, by combining cereals with legumes, the overall protein quality is improved. The Chinese concept of "fan" (rice) and "tsai"(other vegetables) for a balanced and interesting diet is seen throughout the world (Campbell-Platt 1994).

Importance and Benefits of Fermented Cereals

Fermented foods contribute to about one-third of the diet worldwide (Campbell-Platt 1994). Cereals are particularly important substrates for fermented foods in all parts of the world and are staples in the Indian subcontinent, in Asia, and in Africa. Fermentation causes changes in food quality indices including texture, flavor, appearance, nutrition and safety. The benefits of fermentation may include improvement in palatability and acceptability by developing improved flavours and textures; preservation through formation of acidulants, alcohol, and antibacterial compounds; enrichment of nutritive content by microbial synthesis of essential nutrients and improving digestibility of protein and carbohydrates; removal of antinutrients, natural toxicants and mycotoxins; and decreased cooking times.

The content and quality of cereal proteins may be improved by fermentation (Wang and Fields 1978; Cahvan et al. 1988). Natural fermentation of cereals increases their relative nutritive value and available lysine (Hamad and Fields 1979) (Fig. 4). Bacterial fermentations involving proteolytic activity are expected to increase the biological availability of essential amino acids more so than yeast fermentations which mainly degrade carbohydrates (Chaven and Kadam 1989). Starch and fiber tend to decrease during fermentation of cereals (El-Tinay et al. 1979). Although it would not be expected that fermentation would alter the mineral content of the product, the hydrolysis of chelating agents such as phytic acid during fermentation, improves the bioavailability of minerals. Changes in the vitamin content of cereals with fermentation vary according to the fermentation process, and the raw material used in the fermentation. B group vitamins generally show an increase on fermentation (Chavan et al. 1989) (Fig. 5). During the fermentation of maize or kaffircorn in the preparation of kaffir beer, thiamine levels are virtually unchanged, but riboflavin and niacin contents almost double (Steinkraus 1994).

Reddy and Pierson (1994), reviewed the effect of fermentation on antinutritional and toxic components in plant foods. Fermentation of corn meal and soybean-corn meal blends lowers flatus producing carbohydrates, trypsin inhibitor and phytates (Compreeda and Fields 1981; Chompreeda and Fields 1984). However, fermentation of cereals with fungi, such as Rhizopus oligosporus, has been reported to release bound trypsin inhibitor, thus increasing it’s activity (Wang et al. 1972). Fungal and lactic acid fermentations have also been reported to reduce aflatoxin B₁, sometimes by opening of the lactone ring which results in complete detoxification (Nout 1994).

Another benefit of fermentation is that frequently the product does not require cooking or the heating time required for preparation is greatly reduced (Steinkraus 1994).

Figure 4 – Influence of natural fermentation of cereals on available lysine. 

Data from Hamad and Fields (1979)

 

Figure 5 – Influence of natural fermentation of cereals on the thiamine content. 

Data from Chavan and Kadam (1989)

Need for Additional Research

Some advantages of traditional fermentations are that they are labor-intensive, integrated into village life, familiar, utilize locally produced raw materials, inexpensive, have barter potential and the subtle variations resulting, add interest and tradition to local consumers. From this perspective, research leading to new fermentation technologies should be sensitive to social and economic factors in developing countries. Rapid displacement of traditional foodstuffs in developing countries with technologies developed in more affluent countries may result in centralised production, distribution problems, less local involvement in food processing, less employment in some areas, less nutritionally adequate substitutions in raw materials, displacement of traditional arts, loss of unique local know-how, dependence on importation of equipment and materials, initially require the use of outside consultants, and may otherwise not meet local needs as fully as traditional fermented products. On the other hand, indigenous fermentations may have a number of problems, i.e., they are uncontrolled and often unhygenic, labor intensive, seen as primitive by some people, are normally not integrated into the economic mainstream, difficult to tax, have limited export potential (Wood 1994) and in some cases, the impact on nutritive value and safety is questionable.

Specific microflora involved with indigenous fermentations is, in many cases, not known at this time. Specific information on microflora appears to be lacking for several indigenous fermented cereal products. The microbiology of many of these fermentations is undoubtedly quite complex. Many indigenous cereal fermentations involve the combined action of bacteria, yeast and fungi. Some microflora may participate in parallel while others may participate in a sequential manner with a changing dominant flora during the course of the fermentation. The specific microflora involved may vary somewhat from village to village and from family to family within the same village. The identification of specific microflora involved is needed to amplify and control such positive factors as the excretion of lysine by strains of Lactobacillus plantarum (Newman and Sands 1984) and the metabolic detoxification of mycotoxins by Rhizopus oryzae (Nout 1994); as well as to minimize or prevent negative factors such as growth and metabolism of pathogenic and toxinogenic bacteria, e.g., bongrek acid and toxoflavin formation by Pseudomonas cocovenenans (Ko 1985). Identifying and providing a practical means of using appropriate starter cultures is advantageous due to the competitive role of microorganisms and their metabolites in preventing growth and metabolism of unwanted microorganisms. A strong starter may reduce fermentation times, minimise dry matter losses, avoid contamination with pathogenic and toxigenic bacteria and molds, and minimize the risk of incidental microflora causing off-flavor, etc. According to Nout (1994) optimization of starter cultures may be achieved by either conventional selection and mutation, or by recombinant-DNA techniques to result in increased levels of safety. Relatively litle is known of the contribution of microflora to the formation of desired flavor notes during such fermentations. Genes for flavor and other beneficial enzymes that come from incidental microflora may be incorporated into starter bacteria to facilitate more subtle and ancillary aspects of the fermentation along with primary events such as lactic acid production, thus preserving the distinctive nature of products made in different regions.

The contribution of specific enzymes to indigenous cereal fermentations is perhaps even less understood than that of microorganisms. It is likely that there is considerable synergy between complimentary enzymes from the cereal itself and from the microorganisms. One known example of this is the reduction of phytates resulting from 6-phytases of cereal origin and 3-phytases of microbial origin (Reddy and Pierson 1994). Another is the synergy of cereal enzymes and yeast in bread making (Fox and Mulvihill, 1982). It is interesting that fermentation of cereals (e.g. breadmaking and brewing) in the Western world was adversely affected in some ways by the introduction of modern dehydration and storage techniques that minimized fungal contamination and incipient germination. Partial germination of cereal in the field and contamination with otherwise innocuous fungal contaminants contribute enzymes, notably a-amylase and proteases, that aid these fermentations. Today, essentially all beer production and continuous breadmaking in the West is achieved with the aid of added enzymes (Tucker and Woods 1995). A similar situation may occur in developing countries, i.e. as improvements in cereal handling are introduced to minimise postharvest losses and mycotoxin formation, the otherwise improved crop may be less suitable in some ways for traditional fermentations. Hence, basic information is need on the contribution of cereal enzymes and other constituents to indigenous fermentations. With this information in hand, consideration can then be given to use of enzyme supplements and other additives to improve the rate and quality of fermentations.

Another consideration for future research is the contribution of the aforementioned enzyme inhibitors in cereal fermentations. In addition to their already discussed significance as antinutrients in the finished product; protease, amylase and other enzyme inhibitors are expected to influence the rate and extent of important bioconversions that occur during indigenous fermentations. The concentration and spectrum of enzyme inhibitors varies considerably between cereal cultivars (Izquirdo-Pulido et al. 1994). Not withstanding the benefits of the continual introduction of new cereal varieties (Meikle and Scarisbrick 1994), given the genes for enzyme inhibitors are part of the defensive system of plants against insects and other pests, it is possible that introduction of "improved" cereal cultivars in developing countries may adversely affect the utility of cereals for indigenous fermentation. For this reason, basic research on the participation of cereal enzyme inhibitors in the process may provide useful insights on the need for including tests for inhibitors prior to introducing new varieties in areas that extensively utilise cereal fermentations to produce staple foodstuffs.

As pointed out by Wood (1994), there is a possible backlash if consumers in developing countries abandon traditional fermented foods for "smart," sophisticated products popularized in Europe and America. For example, the replacement of indigenous fermented cereal drinks with cola beverages could have a significant negative impact on daily nutrition of many consumers in developing countries. Study of traditional fermentations will undoubtedly yield new information that will expand our global knowledge of science and impact technology throughout the world. Thus, basic research of indigenous cereal fermentations will lead to "inward" as well as "outward" technology transfer.

CONCLUSIONS

Traditional fermentations are likely to remain an important part of global food supply; many may evolve into fermentations involving the use of starter cultures, enzyme additives and controlled environmental conditions, and others may benefit from genetic modification of the cereal or starter bacteria.

Further research should be directed towards identifying the benefits and risks associated with specific indigenous fermented cereals; elucidating the contributions of microorganisms, enzymes and other cereal constituents in the fermentation process; and developing starter cultures, unique microbial strains for nutritive improvement and detoxification, and testing of new cereal varieties for their suitability as fermentation substrates.

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NUTRITIONAL QUALITY OF CEREALS

Cereals, together with oil seeds and legumes, supply a majority of the dietary protein, calories, vitamins, and minerals to the bulk of populations in developing nations (Chaven and Kadam 1989). Some components of cereal nutritive value are summarized in Table 9. The following synopsis of cereal nutrition has been adopted from a review by Chavan and Kadam (1989). Cereal grains are low in total protein compared to legumes and oilseeds. Lysine is the first limiting essential amino acid for man; although rice, oats and barley contain more lysine than other cereals. Corn protein is also limiting in the essential amino acid tryptophan, while other cereals are often limiting in threonine. The annual global yield of essential amino acids from major cereals has been compared to a hypothetical population of 3 billion adults and 2 billion children (Phillips 1997) (Table 10). Accordingly, if all cereals were effectively and fully utilized for human consumption they would more than meet man’s needs for essential amino acids.

Table 9. Comparative nutritive value of cereal grains ¹

FACTOR	Wheat	Maize	Brown rice	Barley	Sorghum	Oat	Pearl millet	Rye
Available CHO (%)	69.7	63.6	64.3	55.8	62.9	62.9	63.4	71.8
Energy (kJ/100 g)	1570	1660	1610	1630	1610	1640	1650	1570
Digestible energy (%)	86.4	87.2	96.3	81.0	79.9	70.6	87.2	85.0
Vitamins (mg/100 g)
Thiamin	0.45	0.32	0.29	0.10	0.33	0.60	0.63	0.66
Riboflavin	0.10	0.10	0.04	0.04	0.13	0.14	0.33	0.25
Niacin	3.7	1.9	4.0	2.7	3.4	1.3	2.0	1.3
Amino acids (g/16 g N)
Lysine	2.3	2.5	3.8	3.2	2.7	4.0	2.7	3.7
Threonine	2.8	3.2	3.6	2.9	3.3	3.6	3.2	3.3
Met. & Cys.	3.6	3.9	3.9	3.9	2.8	4.8	3.6	3.7
Tryptophan	1.0	0.6	1.1	1.7	1.0	0.9	1.3	1.0
Protein quality (%)
True digestibility	96.0	95.0	99.7	88.0	84.8	84.1	93.0	77.0
Biological value	55.0	61.0	74.0	70.0	59.2	70.4	60.0	77.7
Net protein utilil.	53.0	58.0	73.8	62.0	50.0	59.1	56.0	59.0
Utilization protein	5.6	5.7	5.4	6.8	4.2	5.5	6.4	5.1

¹ Adapted from Chavan & Kadam (1989)

Table 10. Annual Global Yield of Essential Amino Acids From Major Cereals and Global Human Requirements¹

AMINO ACID	Wheat kg x 1000	Rice kg x 1000	Maize kg x 1000	Sorghum kg x 1000	Total kg x 1000	Human Requirement kg x 1000	% Provided
Lysine	130	85	104	8	327	223	147
Met. & Cystine	162	78	135	11	386	158	244
Threonine	132	90	140	13	376	138	272
Isoleucine	219	85	143	14	461	158	292
Tryptophan	60	26	27	4	118	34	347
Valine	209	127	189	16	540	148	365
Leucine	313	189	484	47	1033	230	449
Phen. & Tyr.	404	199	339	30	972	164	593

¹ Adapted from Phillips (1997). Yield of amio acid from cereals is global production x amino acid profile x digestibility; human requirement is based on hypothetical population of 3 billion adults and 2 billion children; % provided is the calculated global production from wheat, rice, maize and sorghum divided by estimated global requirement by the hypothetical human population.

Barley, sorghum, rye and oat proteins have lower digestibilities (77-88%) than those of rice, maize and wheat (95-100%). The biological value and net protein utilization of cereal proteins is relatively low due to deficiencies in essential amino acids and low protein availability (Chaven and Kadam 1989). The digestible energy of rice is significantly better than that of other cereals (Table 9). 

Cereals also provide B-group vitamins and minerals, although refining results in losses of these nutrients (Miller 1996) (Table 11). The endosperm of wheat contains only about 0.3% ash. Phosphorous, potassium, magnesium, calcium and traces of iron and other minerals are found in cereals (Bowers 1992). Barley and wheat provide 50 and 36 mg Ca/100 g respectively. Barley provides 6 mg of iron per 100 g; millet provides 6.8; oats, 4.6 and wheat, 3.1. In contrast, soybeans provide more of these nutrients, i.e., Ca (210 mg/100 g) and Fe (7 mg/100 g) (Haard and Chism 1996). Some grains, notably barley, sorghum, and oats, contain appreciable amounts of crude fiber (Table 2) and are referred to as coarse grains. The nutritive and sensory value of cereal grains and their products are, for the most part, inferior to animal food products. Methods that can be employed to improve the nutritive value of cereals include traditional genetic selection, genetic engineering, amino acid and other nutrient fortification, complementaion with other proteins (notably legumes), milling, heating, germination and fermentation.

Table 11. Influence of milling on the trace mineral content of wheat ¹

MINERAL	Whole wheat mg/100 g	White Flour mg/100 g	Wheat Germ mg/100 g	Wheat bran mg/100 g	Loss %
Iron	4.3	1.1	6.7	4.7-7.8	76
Zinc	3.5	0.8	10.1	5.4-13.0	78
Manganese	4.6	0.7	13.7	6.4-11.9	86
Copper	0.5	0.2	0.7	0.7-1.7	68
Selenium	0.06	0.05	0.11	0.05-0.08	16

¹ Adapted from Miller (1996)

ANTINUTRIENTS AND TOXIC COMPONENTS IN CEREALS

Cereals and other plant foods may contain significant amounts of toxic or antinutritional substances. In this regard, legumes are a particularly rich source of natural toxicants including protease inhibitors, amylase inhibitors, metal chelates, flatus factors, hemagglutinins, saponins, cyanogens, lathyrogens, tannins, allergens, acetylenic furan and isoflavonoid phytoalexins (Pariza 1996). Most cereals contain appreciable amounts of phytates, enzyme inhibitors, and some cereals like sorghum and millet contain large amounts of polyphenols and tannins (Salunkhe et al. 1990). Some of these substances reduce the nutritional value of foods by interfering with mineral bioavailability, and digestibility of proteins and carbohydrates. Since legumes are often consumed together with cereals, proper processing of cereal-legume mixtures should eliminate these antinutrients before consumption (Chaven and Kadam 1989; Reddy and Pierson 1994). Relatively little is known about the fate of antinutrients and toxicants in traditional fermented foods.

Phytates

Phytic acid is the 1,2,3,4,5,6-hexaphosphate of myoinositol that occurs in discrete regions of cereal grains and accounts for as much as 85% of the total phosphorous content of these grains. Phytate reduces the bioavailability of minerals, and the solubility, functionality and digestibility of proteins and carbohydrates (Reddy et al. 1989). Fermentation of cereals reduces phytate content via the action of phytases that catalyze conversion of phytate to inorganic orthophosphate and a series of myoinositols, lower phosphoric esters of phytate. A 3-phytase appears to be characteristic of microorganisms, while a 6-phytase is found in cereal grains and other plant seeds (Reddy and Pierson 1994). 

Tannins

Oligomers of flavan-3-ols and flavan-3,4-diols, called condensed tannins, occur widely in cereals and legumes (Haard and Chism 1996). These compounds are concentrated in the bran fraction of cereals (Salunkhe et al. 1990). Tannin-protein complexes can cause inactivation of digestive enzymes and reduce protein digestibility by interaction of protein substrate with ionizable iron (Salunkhe et al. 1990). The presence of tannins in food can therefore lower feed efficiency, depress growth, decrease iron absorption, damage the mucosal lining of the gastrointestinal tract, alter excretion of cations, and increase excretion of proteins and essential amino acids (Reddy and Pierson 1994). Dehulling, cooking and fermentation reduce the tannin content of cereals and other foods.

Saponins

These sterol or triterpene glycosides occur widely in cereals and legumes (Shiraiwa et al. 1991). Saponins are detected by their hemolytic activity and surface active properties. Although the notion that they are detrimental to human health has been questioned (Reddy and Pierson 1994), they have been reported to cause growth inhibition (Cheeke 1976).

Enzyme Inhibitors

Protease and amylase inhibitors are widely occurent in seed tissues including cereal grains. Trypsin-, chymotrypsin-, subtilisin-inhibitor, and cysteine-protease inhibitors are present in all major rice cultivars grown in California, although the individual inhibitor amounts are quite varaiable and are concentrated in the bran fraction (Izquerdo-Pulido et al. 1994). They are believed to cause growth inhibition by interfering with digestion, causing pancreatic hypertrophy and metabolic disturbance of sulfur amino acid utilization (Reddy and Pierson 1994). Although these inhibitors tend to be heat stable, there are numerous reports that trypsin inhibitor, chymotrypsin inhibitor, and amylase inhibitor levels are reduced during fermentation (Chaven and Kadam 1989; Reddy and Pierson 1994).

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