1.7 Fermentation
1.7.7 Fermentation in Africa
1.7.7.1 Food and health situation in Africa
According to the FAO, about 795 million people are undernourished globally. However, hunger and malnutrition are prevalent among majority of the poorest sub Saharan countries (FAO et al., 2015). Hunger is based on the lack of calories as result of insufficient or lack of consumption of enough food that supplements the body with the required energy and nutrition. Micronutrient deficiencies are the so-called ‘hidden-hunger’ and affect approximately 2 billion people worldwide (Burchi et al., 2011). Good nutritional status is vital for the proper functioning of the body immune system, however, malnutrition tends to weaken the natural immunity, hence increasing disease progression and even death. Children are mostly affected by chronic malnutrition, since they have increased nutritional requirements, concurrent with a less developed immune system. Due to this fact, simple infectious diseases, as a result of poor hygienic conditions, usually result in death (Black & Bryce, 2003). Malnutrition is suspected to contribute more than one third of worldwide deaths of all children (Bain et al., 2013; Kalipeni, 2000; Nannan et al., 2007). It is estimated that in 2013, about 6.3 million children under 5 years died, of which 2.9 million were from Africa (WHO, 2013).
1.7.7.2 African fermented foods
The African continent has a wide variety of traditional fermented foods; especially those based on plant substrate materials. In Africa, fermentation has an age old history with the richest
22 variety of fermentations being the lactic acid fermented foods. These foods usually have a large impact on the nutritional health and social economic status of the people (Franz et al., 2014). There are three different traditional food habits in the world that are based on staple cereal dietary cultures: i.e. the eastern food culture diets of cooked-riced, the Western and Australian food culture of wheat/barley-based breads/loaves and the African and south American culture of maize/sorghum/millet porridges (Fusco et al., 2017; Tamang & Kailasapathy, 2010). Fermentation of African foods is usually performed using minimal technology often on a small scale and household basis, characterized by the use of simple, non-sterile equipment, chance or natural inoculas, unregulated conditions, sensory fluctuations, poor durability and unattractive packing of the processed products, resulting in food of unpredictable quality (Oguntoyinbo et al., 2016; Wafula et al., 2016).
The variety of foods and diverse cultures encountered in Africa make it difficult to select a specific type of food for the whole population. Each area has its own regional favourite foods that depends on customs, tradition and religion (Adebayo et al., 2010). The fermentation processes for these foods constitute a vital knowledge for the indigenous food preservation, acquired from observations and experience, and passed on from generation to generation (Aworh, 2008; Chelule et al., 2010). Cereals and root tubers are the most important source of food in Africa, constituting over 80 % of the average diet (Onwueme & Sinha, 1991). With increasing industrialization and urbanization, efforts are presently geared towards the development of large-scale, factory production facilities for these foods, where the quality of the finished product will be assured (Agarry et al., 2010). The most popular African fermented raw foods are crops, cereals, oil seeds, roots and milk (Oyewole, 1997). Fish, meat and vegetables are also fermented in Africa, but not as frequently as in Europe and Asia (Lee, 1997; Oyewole, 1997). Milk fermentation in Africa is mostly practiced in the Savannah, Sahara, Northern, and in rift valleys of East Africa regions, usually with addition of wood ash, blood or leafy vegetables in fermentation vessels that are usually treated with wood smoke (Fusco et al., 2017). Fermentation of milk products (e.g., yoghurt, cheese) are not similar to those typically found in Europe or North America (Fusco et al., 2017; Olasupo et al., 2010).
Fermented food in Africa can be classified on the basis of the substrate used for their preparation or the nature of the finished products (Oguntoyinbo et al., 2016; Olasupo et al., 2010) into the following: 1) fermented, non-alcoholic, cereal based products, 2) starchy root crops, 3)
23 fermented animal protein, 4) fermented vegetable proteins 5) alcoholic beverages and 6) fermented fruits and leafy vegetables Table 1.3 (Fusco et al., 2017). In the fermented non-alcoholic cereals, the main substrates used in fermentation are usually maize, millet and sorghum, which are fermented through natural/spontaneous fermentation (without addition of starter culture) or without backslopping (Fusco et al., 2017). They usually account for up to 80 % of the total energy consumption in many African countries. Fermented foods serve as a staple diet for adults and as weaning foods for infants (Fusco et al., 2017). Fermentation is usually carried out by lactobacilli, particularly Lb. plantarum, Lb. fermentum, Lb. delbrueckii, Pediococcus and Weissella spp., and occasionally yeast and moulds are involved (Tab.1.3). LAB fermented cereal-based African foods maybe classified based on two factors: i.e. the raw cereal ingredients used for preparation, examples include: maize-based foods such mahewu (South Africa), ogi (Nigeria / West Africa), kenkey (Ghana), uji (east Africa), potopoto (Congo), gowé and mawe (Benin); b) millet based foods such as kunu-zaki (Northern Nigeria), mbege (Tanzania), dégué and ben-saalga (Burkina Faso); c) sorghum based foods such as ogi-baba (West Africa), ting (Botswana), injera (Ethiopia) bogobe (Botswana), humulur (Sudan), kisra (Sudan) and hussuwa (Sudan);and d) wheat-based foods such as bouza, kishk or kishj Egypt (Tab.1.3), or the fermented product texture (Nout, 2009; Oyewole, 1997; Olasupo et al., 2010).
In the African fermented starchy roots, cassava (Manihot esculenta) is the main substrate for making a wide range of fermented products like gari, fufu and lafun, consumed commonly in West Africa and agbelima in Ghana (Caplice & Fitzgerald, 1999; Kostinek et al., 2007), kivunde and chikwangue in East Africa (Kimaryo et al., 2000; Padonou et al., 2009) (Tab.1.3). The common LAB associated with starchy roots fermentation usually are Leuconostoc, Lb. plantarum and Lb.
fermentum strains (Kostinek et al., 2008). Cassava fermentation facilitates a detoxification process by breaking down cyanogenic glucosides (linamarin and lotaustralin) which occurs by endogenous linamarase activity, resulting in safe final products (Kostinek et al., 2008) Fermentation of animal proteins in Africa is mostly associated with milk, although fish fermentation is also practiced at a lesser scale (Fusco et al., 2017). The common LAB associated with milk fermentation includes;
Lactococcus lactis, Streptococcus thermophilus, Lb. plantarum, Lb. paracasei, Lb. acidophilus, and Lb. delbrueckii and yeasts such as S. cerevisiae and Candida spp. (Franz et al., 2014; Gonfa et al., 2001; Mathara et al., 2004). In Africa, milk fermentation is done on a rural and tradition-based, small–scale level, to convert milk into varying products with extended shelf life. Different milk
24 products are produced from different parts of Africa, for example: Amasi is a traditional fermented milk consumed in South Africa and Zimbabwe and it’s prepared by fermenting raw milk for several days in calabashes made of gourd, or in stone jars (Chelule et al., 2010). In Ethiopia, raw milk is traditionally fermented into products such as ergo (fermented sour milk), ititu (fermented milk curd), kibe (local butter), neterkibe (kibe or traditional ghee), ayib (cottage cheese), and arera (sour defatted milk) ( Gonfa et al., 2001; Fusco et al., 2017). In Kenya, the Maasai consume kule naoto, a fermented product from Zebu cow milk (Mathara et al., 2004). Other African fermented animal protein products are shown in table 1.3 below.
Fermented legumes and oilseeds are usually fermented Africa vegetable proteins (Fusco et al., 2017). Bacillus spp. are commonly involved in fermentation via alkaline hydrolysis of the proteins to amino acids and ammonia (Olasupo et al., 2010). Alkaline-fermented food condiments in Africa are prepared from seeds from several wild trees (Achi, 1992; Ogunshe et al., 2007; Ouoba et al., 2004), as well as from various cultivated plant seeds. Raw materials used for vegetable protein fermentations in Africa include soy beans, roselle (Hibiscus sabdariffa) seeds, Bambara groundnut, melon (Citrullus vulgaris) cotton seeds (Gossypium hirsutum L.), castor oil bean (Ricinus communis), African locust bean (Parkia biglobosa), African mesquite (Prosopis Africana), cotton seed (Gossypium hirsutum) and African oil bean (Pentaclethra macrophyla), Saman tree (Albizia saman) and Baobab tree (Adansonia digitate) (Fusco et al., 2017) ) (Tab.1.3). Africa is rich in different fruits and leafy vegetables containing high amounts of nutrients and micronutrients (Oguntoyinbo et al., 2016). It is conceivable, therefore, that efforts for the fermentation of e.g.
cowpea, sorghum, spider plant, nightshade or kale leaves are intensified, in order to preserve the nutrients and prevent postharvest losses of such highly perishable products. Some examples of known African leaf fermentations are shown in table 1.3. The reported microorganisms associated with these fermentations were a mixture of a variety of yeasts and bacteria such as lactobacilli, micrococci, staphylococci and propionibacteria. This point to the fact that in these fermentations a predominating lactic acid microbiota cannot establish itself and that the microorganisms, which predominate in the fermentation, may possibly depend on which microorganisms were initially present on the raw materials.
25 Table 1.3: Types of African fermented food with the microorganisms involved in fermentation (alcoholic beverages are not included)
Fermented product
Region of
production Raw substrate Microorganisms involved in fermentation
African fermented cereal-based non-alcoholic foods
Ogi Nigeria, Benin Maize, sorghum or millet Ped. pentosaceus, Lb. fermentum Lb. plantarum, yeasts
Koko and Kenkey Ghana Maize, sorghum or millet Weissella confusa, Lb. fermentum, Lb. salivarius, Pediococcus spp., yeasts Mahewu (magou) South Africa Maize, sorghum or millet Lb. delbrueckii, Lb. bulgaris, Leuconostoc spp.
Uji East Africa Maize, sorghum or millet Lb. plantarum, Lb. paracasei, P. pentosaceus, Leuconostoc spp.
Kisra Sudan Sorghum Lactic acid bacteria
Injera Ethiopia Sorghum Candida guillermondii
Ting Botswana Sorghum Lb. fermentum, Lb. plantarum, Lb. rhamnosus
Obusera Uganda Millet Lactic acid bacteria
Mawe Benin Maize, sorghum or millet Lact. lactis, Ped. pentosaceus, Lb. plantarum
Hussuwa Sudan Sorghum Lb. fermentum, Ped. acidilactici
Bogobe Botswana Sorghum Unknown
Kunu-Zaki Nigeria Millet, sorghum Lb. fermentum, P. pentosaceus, W. confusa, Enterococcus faecalis
Potopoto Congo Maize
Lb. gasseri, Lb. plantarum, Lb. acidophilus, Lb. delbrueckii, Lb. reuteri, Lb.
casei, Bacillus spp., Enterococcus spp.
Dégué Burkina Faso Millet Lb. gasseri, Lb. fermentum, Lb. brevis, Lb. casei, Enterococcus spp.
Ben Saalga Burkina Faso Millet Lb. plantarum and other lactic acid bacteria
Fermented starchy root products
Gari West Africa Cassava
Lb. plantarum, Leuc. fallax, Lb. fermentum, W. paramesenteroides, Lb. brevis, Strep. lactis
Fufu Nigeria Cassava Ped. pentosaceus, Lb. fermentum, Lb. plantarum
Kivunde Tanzania Cassava Lb. plantarum, other LAB, yeast
Lafun Nigeria Cassava Lb. fermentum, Lb. plantarum, W. confusa, yeast
Chikawngue Zaire Cassava LAB, yeast
Cingwada East and Central Cassava Unknown
26 Africa
Kocho Ethiopia
Ensette or Abyssinian banana
(Ensette ventricosum) LAB, yeast
Agbelima Ghana Cassava
Lb. plantarum, Lb. brevis, Lb. fermentum, Leuc. mesenteroides, Bacillus sp., yeast
Fermented animal proteins
Nono (milk curd) N. West Africa Milk Lactic acid bacteria
Maziwa lala East Africa Milk Lactococcus lactis, Strep. thermophilus
Leban (sour milk) Morocco Milk
Lactic streptococci (lactococci), Leuc. lactis, Leuc. mesenteroides subsp.
Cremoris
Wara West Africa Milk Lac lactis, Lactobacillus spp.
Ergo Ethiopia Milk Lactobacillus spp., Lactococcus spp.
Kule naoto Kenya Milk
Lb. plantarum, Lb. fermentum, Lb. paracasei, Lb. acidophilus, lactococci, leuconostocs and enterococci
Sethemi South Africa Milk Lactobacilli, lactococci, yeast
Guedj Senegal Fish Lac. lactis
Bonome (stink
fish) Ghana Fish Unknown
Fermented vegetable proteins Dawadawa or iru West Africa
African locust bean (Parkia
biglobosa), Soybean Bacillus subtilis, B. licheniformis
Ogiri Nigeria Melon (Citrullus vulgaris) Bacillus spp., (predominant), Proteus, Pediococcus Ogiri-nwan Nigeria
Fluted pumpkin bean (Telfaria
occidentalis) Bacillus spp.
Ogiri-igbo Nigeria
Castor oil seed (Ricinus
communis) Bacillus subtilis, B. megaterium, B. firmus Ogiri-saro.(sigda) Sierra Leone, Sudan Sesame seed Bacillus spp.
Ogiri-okpec/okpehe Nigeria Mesquite (Prosopsis africana) Bacillus spp.
Ugba.(Apara) Nigeria
African oil bean (Pentaclethra
macrophylla) Bacillus subtilis, Micrococcus spp.
27
Owoh Nigeria
Cotton seeds (Gossypium
lursutum) Bacillus spp.
Bukalga
Niger, Mali, Sudan, Burkina Faso
Kartade, red sorrel (Hibiscus
sabradiffa) Bacillus subtilis
Fermented fruits and leafy vegetables
Kawal Sudan
Fresh leaves of Cassia obtusifolia
Bacillus subtilis and Propionibacterium spp. (dominant), Lb. plantarum, Candida krusei and Saccharomyces spp.
Ntoba mbodi Congo
sun-drying cassava leaves and papaya leaves
Micrococcus varians, Bacillus macerans, Bacillus subtilis, Staphylococcus sciuri and Staphylococcus xylosus
Agadagidi Nigeria
ripe plantain (Musa paradisiaca)
pulp Leuconostoc and Streptococcus (dominant) Bacillus, Micrococcus and yeast
mudetemwa Zimbabwe
fruits of the sand apple (Parinari curatellifolia
palm wine Africa
palm sap of Rafia guinensis and Borassus akeassii
Micrococcus, Leuconostoc, Streptococcus, Lactobacillus, Acetobacter, Serratia, Aerobacter (Klebsiella), Bacillus, Zymomonas and Brevibacterium and yeasts
Masau fermented
fruit pulp Zimbabwe
Ziziphus mauritiana fruit (locally called masau)
Lactobacillus agilis, Lb. plantarum (dominant), Lactobacillus bifermentans, Lactobacillus minor, Lactobacillus divergens, Lactobacillus confusus,
Lactobacillus hilgardii, Lactobacillus fructosus, Lb. fermentum, Streptococcus spp. and yeasts
28
29 1.7.7.3 Fermentation of African leafy vegetables
1.7.7.3 Fermentation of African leafy vegetables
There is limited information on the use of LAB starter cultures in the fermentation of AILVs in SSA. There are, however, various studies on the development of starter cultures for other fermented foods consumed in other countries, such as uji (Mbugua et al., 1984), gari (Kostinek et al., 2008), kivunde (Kimaryo et al., 2000) and ogi (Teniola & Odunfa, 2001). The fresh leafy vegetables are usually processed immediately and consumed. Sun drying is the common preservation method in Africa for leafy vegetables. However, this method results in the loss of vital nutrients. The study by Muchoki et al. (2007) fermented cowpea leaves, using the plants naturally occurring microbiota as source of starter microorganisms for 21 days. The fermentation showed a positive effect in the maintenance of various nutrients. There are recent studies involving prevention and control of postharvest losses of AILVs. Such studies included the fermentation of African kale (Brassica carinata), cowpea (Vigna unguiculata) and African nightshade (Solanum scabrum) leaves with previously isolated LAB from other fermented African food products as starter cultures. The results showed that controlled fermentation of kale, cowpea and nightshade offers a promising avenue to prevent spoilage and to improve the shelf life and safety (Wafula et al., 2015; Oguntoyinbo et al., 2016).
A generalised scheme for vegetable fermentation entails the harvesting of the vegetables followed by sorting and destemming, proper washing to remove soil and insects, and cutting of the vegetables into small pieces, or using it whole (Fig.1.4). Fermentation can be performed in three ways, i.e. either with 2.5-10 % salt, in non-salt solution, or with a mixture of 3-5 % salt-sugar brined solution. The vegetables are fermented in vessels, with addition of the brine solution pre-warmed at 60 oC. Fermentation of vegetables occurs spontaneously by the natural LAB surface microbiota, such as autochthonous Lactobacillus, Leuconostoc and Pediococcus spp. (Steinkraus, 2002) at 25-30 oC for up to 30 days (Fig.1.4). Lactic acid fermentation represents the easiest and the most suitable way for increasing the daily consumption of fresh vegetables (Swain et al., 2014;
Wafula et al., 2016).
30
`
Figure 1.4: Generalised scheme for vegetable fermentation processes (Swain et al., 2014).
1.7.7.4 Importance of vegetable fermentation in Africa
Food fermentation plays an important role in most developing countries from nutrition, health, social and economic perspectives. The climatic conditions in many parts of Africa are usually not optimal for long-term storage and stability of fresh foods (Caplice & Fitzgerald, 1999).
Therefore, fermentation is the simplest way of improving the nutritional, shelf life, sensory and functional qualities (Blandino et al., 2003).
Although most vegetables, especially the grains and legumes, are rich in dietary nutrients, their nutritive value is limited by the presence of several anti-nutritional and toxic substances, including oligosaccharides (especially raffinose, stachyose and verbascose) that are the main cause of
Soaking in brine solution Raw African leafy vegetables
Sorting and destemming
Washing and cutting (5mm thickness)
Salted (2.5-10 %) Mixed 3-5 % salt-sugar
or with other ingredients Non-salted
Soaking in brine Solution Sun drying
Fermentation 1-2 weeks at 10-25 oC Fermentation 5-30 days
at 25-30 oC
Fill into vessels
Drying or freezing
Fermentation 1-2 weeks at 2-10 oC
Drying or freezing
Sun drying or pasteurization Packaging and storage at 18-32 oC
31 flatulence problems. Therefore, legume fermentation results to nutritional benefits as result of LAB breakdown of flatulence causing, indigestible oligosaccharides into absorbable organic acids that are of health benefit to the human body (Granito et al., 2005).
Certain probiotic LAB have been shown to prevent human diarrheal diseases, since they can temporarily modify the composition of intestinal microbiota and strengthen the host immune system (Franz et al., 2014; Mathara et al., 2004), thus preventing the growth of pathogenic enterobacteria. LAB also produce antifungal inhibitory compounds, which are mainly organic acids (Sauer et al., 2013). Research has shown that LAB fermentation is an effective way of removing Gram-negative bacteria from food products, since they are more sensitive to fermentation processing, i.e. to organic acids and low pH (Oguntoyinbo et al., 2016; Mensah, 1997; Motarjemi, 2002; Wafula et al., 2015). LAB thus play a defining role in the preservation and microbial safety of fermented foods, promoting the microbial stability of the final products of fermentation. In most African countries, where resources for cooking and food preservation are scarce, fermentation is highly recommended technique, especially in rural areas. This process is known to alter the composition of food and to soften its texture in such a way, that cooking will need minimal time and energy (Holzapfel, 1997).
Muchoki et al. (2007) fermented cowpea leaves in 16 kg batches for 21 days and then heat treated and solar dried the fermented leaves. The fermentation, heat-treatment and drying were shown to retain substantial levels of β-carotene and ascorbic acid. Kasangi et al. (2010) also fermented cowpea leaves and studied the fermentation kinetics. By adding 3 % glucose to the leaves, a fermentation with the highest concentration of lactic acid of 0.6 % and with a low pH of 4.7 could be obtained. The study concluded that fermentation, in conjunction with solar drying, has potential for small-scale farmers to enhance the product keeping quality, as well as nutrient quality (Kasangi et al., 2010). Cowpea, African nightshade and kale leaves were fermented in 1 litre beakers for 5 days to determine the role of the starter cultures Lb. plantarum BFE 5092 and Lb.
fermentum BFE 6620 to inhibit the growth of pathogens Listeria monocytogenes and Salmonella Enteritidis. Fermentation was conducted on 100 g of the leaves and 3 % salt + 3 % sugar brine solution and inoculated with 1 x 107 cfu/ml starter cultures and 1 x 103 cfu/ml pathogens. The results showed that fermentation of African indigenous vegetables with selected starter cultures
32 inhibits the growth of pathogens within the first 3 days of fermentation (Wafula et al., 2015;
Oguntoyinbo et al., 2016).