Generally, fermentation is a food preservation method intended to extend shelf-life, improve palatability, digestibility and the nutritive value of food [22, 23, 24]. Lactic acid fermentation comprises of the chemical changes in foods accelerated by enzymes of lactic acid bacteria resulting in a variety of fermented foods [11, 25]. Lactic acid fermentation processes are the oldest and most important economical forms of production and preservation of food for human consumption ([11, 23, 26, 27]. It is, therefore, not surprising that fermented foods and beverages make a big contribution to people’s diets in Africa . It is reported that fermented foods globally contribute 20 to 40% of the food supply and usually, a third of the food consumed by man is fermented . This renders fermented foods and beverages a significant component of people’s diets globally. It is estimated that the largest spectrum of lactic acid fermented foods occurs in Africa [23, 30]. However, in Africa, fermented foods and beverages are often prepared by employing spontaneous fermentation processes at household level or by small-scale industries using maize, sorghum and millet as the main cereals [11, 31, 32]. In sections 3 and 4 of this chapter, a description will be given of acid-fermented cereal-based foods and beverages and the major bacteria involved in the fermentation of such foods. In section 5 of this chapter, probiotic cereal beverages will be dealt with.
2.1. Some beneficial attributes of African fermented cereal-based foods
Lactobacillus species are the predominant organisms involved in the fermentation of cereal-based foods and beverages in Africa (see section 4.1). These organisms are reported to have bacteriostatic, bactericidal, viricidal, anti-leukaemic and antitumor effects in the consumer [25, 28, 33]. Beneficial starter cultures are not usually used in the fermentation of traditional cereal-based foods and beverages. However, it is reported that fermented foods have a probiotic potential  due to the probiotic Lactobacillus species that may be contained in them, some of which are of human intestinal origin .
The quality of some traditional African fermented products (see section 3.2) can be enhanced using beneficial cultures. ‘Dogik’ for example is ‘ogi’ enhanced with a lactic acid starter culture reputed to have antimicrobial activities against diarrhoeagenic bacteria . Lactobacillus paracasei ssp. paracasei, a probiotic Lactobacillus species  was present together with other LAB in uji . Strains of Lb. acidophilus, which are probiotic, were also isolated from an African sorghum-based product in which accelerated natural lactic fermentation was observed .
Improved production of milk by nursing mothers has been attributed to consumption of fermented uji, one of the traditional fermented beverages in Africa. Kanun-Zaki, a fermented non-alcoholic cereal-based beverage widely consumed in Northern Nigeria is also popularly believed to enhance lactation in nursing mothers . Restoration of the normal blood level and resultant compensation for blood lost during traditional tribal circumcision operations in parts of Africa is attributed to drinking large quantities of fermented uji .
It is reported that several B vitamins including niacin (B3), panthothenic acid (B5), folic acid (B9), and also vitamins B1, B2, B6 and B12 are released by LAB in fermented foods. These vitamins are co-factors in some metabolic reactions, for instance, folates prevent neural tube defects in babies and provide protection against cardiovascular disease and some cancers .
2.1.1. Shelf-life extension and improved nutritional and sensory properties
Generally, shelf-life, texture, taste, aroma and nutritional value of food products can be improved by fermentation [11, 23, 25, 40, 41]. The metabolic activities of microbial fermenters are responsible for the improvement in taste, aroma, appearance and texture [23, 30]. During fermentation, there is production of lactic, acetic and other acids and this enhances the flavour and lowers the pH of the final product. The acids also prolong food shelf-life by lowering the pH to below 4 and this restricts the growth and survival of spoilage organisms and some pathogenic organisms such as Shigella, Salmonella and E. coli [11, 25, 28, 33, 42]. Fermented foods, unlike non-fermented foods, have a longer shelf-life, making fermentation a key factor in the preservation of such foods [23, 43]. Because fermentation improves keeping quality and nutritional value, it is a predominant food processing and preservation process [44, 45]. During fermentation, enzymes such as lipases, proteases, amylases and phytases are produced and these in turn hydrolyse lipids, proteins, polysaccharides and phytates respectively . The released nutrients contribute to the enhancement of sensory quality and nutritional value of the product [46, 47].
2.1.2. Inhibition of pathogenic microorganisms in fermented foods.
Spontaneous fermentation may involve species of Lactobacillus, Lactococcus, Pediococcus as well as certain yeasts and moulds . Lactic acid bacteria involved in fermentation are able to produce hydrogen peroxide, but lack the true catalase to break down the hydrogen peroxide. The hydrogen peroxide can, therefore, accumulate and be inhibitory to some harmful bacteria and to the LAB themselves .
The organic acids released (e.g. lactic, acetic, propionic and butyric acids), as by-products during lactic acid fermentation, lower the pH to levels of 3 to 4 with a titratable acidity of about 0.6% (as lactic acid) [23, 40, 48]. The undissociated forms of the acetic and lactic acids at low pH exhibit inhibitory activities against a wide range of pathogens [23 48]. This improves food safety by restricting the growth and survival, in fermented cereal beverages, of spoilage organisms and some pathogenic organisms such as Shigella, Salmonella and E. coli [11, 25, 28, 33, 43, 47]. Fermented maize gruel and high-tannin sorghum gruel at pH 3.8 inhibited E. coli, Campylobacter jejuni, Shigella flexneri, Salmonella typhimurium and Staphylococcus aureus . When starter cultures were used to ferment sour maize bread, it was found out that Lb. plantarum lowered the pH to 3.05 . The fermented maize dough also showed growth inhibitory activity against Salmonella typhi, S. aureus, E. coli, and the aflatoxigenic Aspergillus flavus .
Although Koko sour water (KSW) fed to Ghanaian children did not seem to halt diarrhoea, improved well-being was claimed after 14 days of consumption of this product . Conflicting results about the efficacy of fermented beverages against pathogens and diarrhoea is attributed to the unpredictable nature of spontaneous fermentation. Spontaneous fermentation results in a variety of species and strains with varying degrees of antibacterial activity and ability to adhere to intestinal membranes . Other studies have however, reported positive outcomes of consuming fermented cereal beverages. It was reported that a fermented cereal gruel in Tanzania reduced diarrhoea by 40% in consuming children compared to those children that did not consume it over a period of 9 months [44, 48]. This was attributed to better beverage microbial safety as well as protection against intestinal enteropathogenic colonization . In a review by  information gathered revealed that fermented cereal-based products which contained Lactobacillus spp. and lactic acid had viricidal, anti-leukemic, antitumor and antibacterial activities..
Lactobacillus isolates including Lb. fermentum, and Lb. plantarum, from maize-based ogi (West Africa) and Lb. fermentum, Lb. paracasei and Lb. rhamnosus from maize-based boza (Eastern Europe) were active against potential pathogens such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis and Bacillus cereus due to the low pH in these products and the production of bacteriocins by the Lactobacillus spp .
2.1.3. Production of bacteriocins by lactic acid bacteria
Bacteriocinogenic lactic acid bacteria (LAB) isolated from fermented foods produce proteinaceous, antimicrobial substances (Table 1) called bacteriocins [23, 31, 50, 51]. It was reported that bacteriocinogenic LAB prevent the growth of pathogens such as Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus and Clostridium dificile .
Bacteriocins have the ability to form pores in the membrane of target bacteria, in this way exerting bactericidal and bacteriostatic effects against the growth of pathogens in the intestinal tract . Bacteriocins also reduce or prevent post-production microbial contamination of feed and food fermentation products in the food chain . It was observed that bacteriocins from Lb. plantarum and Lb. casei isolated from fermented maize products, kenkey and ogi respectively inhibited and acted against a number of food borne pathogens . However, bacteriocins have a narrow antimicrobial spectrum and of all bacteriocins, nisin produced by Lactococcus lactis is the only one generally used as a preservative by food manufacturers [46, 50]. A range of characterized bacteriocins that have potential benefits, have been reported to be produced by the Lactobacillus spp. and these are referred to in Table 1. While some LAB may show bacteriocin-linked inhibition of food spoilage and pathogenic bacteria in vitro in laboratory media, inhibitory activity in the food matrices may not be equally effective. This may be due to poorer diffusion of the bacteriocin into the cells of pathogenic bacteria in the food matrix or be the result of bacteriocin inactivation by nutrient components in the food .
|Bacteriocin||Bacterial Species||Active against|
|Bulgarican||Lb. delbrueckii subsp. bulgaricus||Broad, including G (-).|
|N.N||Lb. fermentum||Broad G (+) incl Listeria spp|
|Acodophillin||Lb. acidophilus DDS 1||Disease-causing M/Os|
|Lactocidin||Lb. acidophilus||Disease-causing M/Os|
|Acidolin||Lb. acidophilus||Disease-causing M/Os|
|Lactobacillin||Lb. acidophilus||Disease-causing M/Os|
|Lactacin B||Lb. acidophilus||LAB|
|Nisin||Lactococcus lactis||Broad G(+) incl Listeria spp|
|Caseicin 80||Lb. casei||Lb. brevis|
|Plantaricin A||Lb. plantarum||LAB|
|Reuterin||Lb. reuteri||Broad G (+), G (-) and fungi|
Some of the bacteriocins produced by lactic acid bacteria (LAB)
2.1.4. The effect of fermentation on toxic, antinutritional and indigestible compounds in cereal foods
During fermentation, microbial activity may lead to the elimination of toxic compounds from food products [28, 31]. For example it was reported that fermentation with Lb. plantarum starter cultures significantly reduced the cyanogenic glucoside content of cassava . High cyanide content in a diet can cause acute poisoning, tropical ataxic neuropathy and konzo (a paralytic disease). It may also exacerbate iodine deficiency resulting in goitre and cretinism . During ‘gari’ and ‘lafun’ production from cassava, the cyanogenic glucoside, linamarin, is hydrolysed by the linamarinase enzyme to glucose and cyanohydrin. The latter product is then broken down to acetone and hydrocyanic acid by hydroxynitrile lyase at pH 5-6 and the free cyanide is released faster by gentle heating [25, 55]. If the cyanogenic glucoside linamarin were to be hydrolysed in the gastro-intestinal tract (GIT), the released cyanide anion would be absorbed and halt the functioning of cytochrome oxidase enzymes in the body [23, 29].
Legumes and cereals contain indigestible oligosaccharides such as stachyose, verbascose, and raffinose which cause flatulence, diarrhoea and digestion problems . The α-D-galactosidic bonds in the above-mentioned sugars are relatively heat-resistant, but they can be degraded by the galactosidase enzymes of some LAB including strains of Lb. fermentum, Lb. plantarum, Lb. salivarius, Lb. brevis, Lb. buchneri and Lb. cellobiosus . During fermentation, the microorganisms disintegrate these flatulence-causing and indigestible oligosaccharides into utilisable di- and mono-saccharides [25, 29, 53].
Phytic acid, tannins and phenolic acids are polyphenols that are considered to be antinutritional factors (ANFs) and are found in cereals and legumes and the foods prepared therefrom . The ANFs contribute to malnutrition and reduced growth rate due to the promotion of poor protein digestibility and by limiting mineral bioavailability [23, 46, 56, 57]. Phytic acid in cereals and legumes, for example, (Table 2) affects the nutritional quality due to chelation of phosphorus and other minerals such as Ca, Mg, Fe, Zn, and Mo [41, 56, 58, 59]. The resultant low mineral bioavailability can result in mineral deficiency [47, 59]. Deficiency in a mineral such as iron can result in anaemia, a decrease in immunity against disease and impaired mental development. Poor calcium bioavailability on the other hand prevents optimal bone development and can cause osteoporosis in adults. Insufficient zinc brings about recurring diarrhoea and retarded growth .
Approximate phytate content of sorghum, maize, millet and cowpeas
Other negative effects of the presence of phytate in the diet, include the reduction of the activity of digestive enzymes such as trypsin, alpha-amylase and beta-galactosidase in the GIT. This is due to the formation of complexes of phytate with the enzymes and other nutrients that negatively affect digestive processes [57, 58]. Similarly tannins and polyphenols are enzyme inhibitors of plant origin that form complexes with proteins, resulting in deactivation of digestive enzymes, reduction in protein solubility and digestibility and reduction of absorbable ions [57, 60, 61]. The enzymes inhibited by tannins and/or polyphenols include pepsin, trypsin, chymotrypsin, lipases, glucosidase and amylase [57, 62]. Inhibition of the amylase enzymes results in low starch breakdown and hence, less sugar release in the GIT . In fermented products this amylase inhibition by tannins impairs microbial proliferation . This in turn decelerates pH decrease and acidity production in the medium .
Fermentation, by certain LAB and yeasts, removes or reduces the levels of antinutritional factors such as phytic acid, tannins and polyphenols present in some cereals meant for weaning purposes [23, 31, 41, 47, 53, 56, 59, 63]. During fermentation, optimal pH conditions prevail for enzymatic degradation of the antinutritional factors. This results in better bioavailability of minerals such as iron, zinc and calcium [11, 23]. Strains of Lb. plantarum degraded phytic acid in the cereals after incubation at 37 °C for 120 hours . This degradation can be ascribed to the hydrolysis of the phosphate group by phytases from the raw cereal substrate and produced by the fermenting microorganisms [46, 47, 57]. Fermentation alone reduced the phytate content by 39%. The combined effect of fermentation plus the addition of exogenous phytase, resulted in a reduction of 88% of the phytates in tannin sorghum gruel .
Fermentation reduced phenolic compounds and tannins in finger millet by 20% and 52% respectively . Fermentation coupled with methods such as decortication, soaking and germination reduced the tannins in sorghum, other cereals and in beverages made from these cereals [57, 60, 61, 62, 83]. Fermentation of porridges from whole and decorticated tannin sorghum led to significant reduction of total phenols .
The use of Rhizopus oligosporus to ferment cooked soybean in tempe production reduced residual trypsin inhibitor activity (TIA) by 91% in addition to the 86.4% reduction attributed to steaming . The reduction of the TIA was ascribed to hydrolysis of the trypsin inhibitor by the fungi fermenting the tempe . In another study , Lb. brevis, Lb. fermentum, Streptococcus thermophilus and Pediococcus pentosaceus were observed to have improved the nutritional quality of fermented sorghum products. Table 3 shows that some strains of LAB significantly degraded trypsin inhibitors. This illustrates the possibility that using carefully selected probiotic bacteria to ferment cereal foods may reduce the antinutritional factors in such products.
Fermentation can also decrease the activity of the proteinase and amylase inhibitors in cereals resulting in an increase in the availability of starch and essential amino acids such as lysine, leucine, isoleucine and methionine [23, 46, 53]. The protein quality and nutritive value of fermented products such as kenkey; iru; and ugba  and ogi  was improved during fermentation due to either microbial protein synthesis or loss of non-protein material. In support of the above,  reported that fermenting with Lb. plantarum OG 261-5 significantly improved the levels of tryptophan, lysine and tyrosine even though other amino acids such as isoleucine, leucine, valine and phenylalanine decreased.
|LAB isolate||Reduction of TI (mg)||Percent reduction|
|Lb. plantarum 91||2.41||48.0|
|Lb. fermentum 103||1.22||24.4|
|Pediococcus sp. 90||0.89||17.8|
|Pediococcus sp. 19||1.08||21.6|
|Leuconostoc sp. 106||2.68||53.6|
|Lactobacillus sp. 41||0.65||13.0|
|Lactobacillus sp. 17||1.86||37.2|
|Lactobacillus sp. 62||1.34||26.8|
Degradation of trypsin inhibitor (TI) by lactic acid bacteria isolated from *aflata in Ghana
Fermentation in many instances results in an increased vitamin content of the final product . Lactobacilli involved in fermentation may require vitamins for growth, but several of them are capable of bio-synthesizing B-vitamins in excess. It is reported that several B vitamins including niacin (B3), panthothenic acid (B5), folic acid (B9), and also vitamins B1, B2, B6 and B12 are released by LAB in fermented foods . Cereal-based products such as ogi; mageu; and kenkey have thus been reported to have an improved B-vitamin content [25, 29]. Fermentation therefore improves the nutritive value of cereal foods.
2.1.5. Reduction, binding or detoxification of mycotoxins in fermented foods
Maize (Zea mays), sorghum (Sorghum vulgare), pearl millet (Pennisetum glaucum) and finger millet (Eleusine coracana) constitute the most important cereals for the preparation of fermented foods in the developing world [41, 65, 66, 67]. These cereal grains are however, exposed to pre- and post-harvest mycotoxin contamination which end up in the fermented foods [23, 54. 67]. Among the cereals, maize is the most prone to mycotoxin contamination .
Mycotoxins are secondary metabolites released into cereal grains and legume seeds by species of the genera Aspergillus, Fusarium and Penicillium [54, 66]. Aflatoxins and fumonisins are the mycotoxins, in cereals, of major health and economic concern in the developing world [23, 24, 48, 54, 66, 68, 69]. Table 4 shows the deaths linked to mycotoxins in foods. Aflatoxin B1 (AFB1) is toxic, carcinogenic, mutagenic and teratogenic [45, 69]. Fumonisins have been linked to oesophageal cancer in South Africa and liver cancer in China [66, 68]. Kwashiorkor in children is aggravated by long term exposure to aflatoxin . The development and propagation of cereal-based probiotic and/or synbiotic (prebiotics and probiotics combined) beverages may consequently, to some extent, be hampered by mycotoxin-contamination of the cereals used in making such beverages.
Bacterial and fungal (biological) decontamination is one of the mycotoxin-reducing strategies that have been and are being investigated . Flavobacterium aurantiacum (Nocardia corynebacterioides), Corynebacterium rubrum, Saccharomyces cerevisiae, Candida lipolitica, Candida krusei, Aspergillus niger, Mucor spp., Rhizopus spp., Nurospora spp., Amillariella tabescens, and Trichoderma viride are bacterial and fungal species reported to have the capability to degrade mycotoxins enzymatically ([23, 24, 45, 69]. Extracellular extracts of Rhodococcus erythropolis reduced Aflatoxin B1 (AFB1) by 66.8% after 72 hours of incubation . Fermentation by R. oryzae and R. oligosporus was reported to reduce aflatoxins to aflatoxicol A which, under conditions created by organic acids, gets permanently converted to aflatoxicol B . It was claimed that aflatoxin B1 is 18 times more toxic than aflatoxicol B and it is also possible that the former, during lactic acid fermentation to pH < 4.0, gets transformed into a less toxic isomer, aflatoxin B2 .
A heat-treated Saccharomyces yeast species was said to absorb more than 90 % (w/w) of ochratoxin A in grape juice while live cells could only bind 35 % (w/w) [24, 45]. Other workers have indicated that binding of Aflatoxin B1 was better at low pH and when cells were subjected to acid or heat treatment . The implication is that food beverage preparation, which involves cooking after fermentation, together with the highly acidic conditions of the fermented food beverage, may physically alter the microbial cell structure thereby increasing the binding sites for AFB1 . This provides a way of reducing aflatoxins in African fermented foods and beverages. However, some of the microorganisms indicated in the above paragraphs may not necessarily be GRAS (generally recognised as safe) in the human GIT.
|Country||Year||Food source||Mycotoxin content||Percentage of samples contaminated||Mycotoxin||Deaths||Case patients|
|Kenya||NA||3 maize brands||0.4-2.0 µg/Kg||NA||Aflatoxins||NA||NA|
|South Africa||NA||Peanut butter||< 300 ppb||NA||Aflatoxin B1||NA||NA|
|Togo, Benin||NA||Household maize||NA||30%||Aflatoxin B1||NA||NA|
|Nigeria||NA||Maize samples||NA||33%||Aflatoxin B1||NA||NA|
|Benin||NA||Agro-zone sample||"/> 5 µg/Kg||9.9 - 32.2%||Aflatoxins||NA||NA|
|Ghana||NA||Maize silos||20-335 µg/Kg||NA||Aflatoxins||NA||NA|
|Togo, Benin||NA||Maize samples||"/> 100 ppb||50%||Aflatoxins||NA||NA|
Deaths and ill health linked to mycotoxin contamination of samples in African countries
Aflatoxin B1 could not be detected in fermented maize porridge (amahewu) that had been made from maize meal samples containing 0.55 and 0.84 µg/g aflatoxin B1. In the same study, the levels of fumonisin B1, in contaminated maize meal samples containing 12.1, 24.6, 4.1, 20.6, 47.2 µg/g of this mycotoxin, were drastically reduced in fermented maize porridge to levels of 1.4, 1.4, 0, 6.9, 6.3 µg/g respectively . This exemplifies the detoxification potential for cereal beverages by lactic acid fermentation. The mechanism of mycotoxin removal from fermented food matrices is not clear.
Without forgetting the above paragraph relating to the effect of probiotic fermentation on mycotoxin levels, some reports on fermentation-linked reduction of aflatoxins in cereal food matrices are controversial. There are reports indicating no significant aflatoxin reduction during fermentation . It was observed that fermentation only enabled a reduction of 18% and 13% of aflatoxin and fumonisin respectively in ogi . It was reported that under acidic conditions, aflatoxins persist due to aflatoxin precursors and on the other hand, aflatoxin only undergoes reformation but not reduction under acidic conditions created by organic acid metabolites of LAB . There are also fears that fumonisin binds with starch to form an undetectable complex and besides this, they may react with reducing sugar (D-glucose) to form sugar adducts or are hydrolysed to aminopolyols AP1 and AP2 .
The foregoing findings indicate that mycotoxin-reduction in fermented cereal food matrices has not yet been properly elucidated. It is therefore necessary to screen probiotic microbial isolates to find those strains that have a definite potential to degrade aflatoxins during fermentation in food matrices. Such mycotoxin-degrading species need to be fully compatible with the human GIT ecosystem. Some workers recommended the use of probiotic microorganisms with high aflatoxin B1 binding capability in fermented foods . However, binding is not degradation and the binding probiotic cells are consumed along with the food matrix. The fate of bound toxins in fermented food matrices needs to be investigated. Probiotics and/or LAB suitably screened for their biological mycotoxin degradation, among other technological and health benefits could be better applied in human food fermentation, even though, prevention of mycotoxin contamination is the better option. Besides fermentation and contamination-preventive measures, it was noted that processing operations including sorting, winnowing, washing, crushing and dehulling  significantly reduced mycotoxin levels in several cereal foods.