Some of the bacteriocins produced by lactic acid bacteria (LAB)
Functional foods are defined as foods that, in addition to their basic nutrients, contain biologically active components, in adequate amounts, that can have a positive impact on the health of the consumer [1, 2, 3, 4]. Such foods should improve the general and physical conditions of the human organism and/or decrease the risk of occurrence of disease . Functional foods have also been referred to as medicinal foods, nutritional foods, nutraceuticals, prescriptive foods, therapeutic foods, super-foods, designer foods, foodceuticals and medifoods . These foods generally contain health-promoting components beyond traditional nutrients . Various criteria for defining functional foods have been mooted by  and a number of published reports have indicated the benefits of functional foods to the consumer [7, 8].
One way of creating a functional food is by inclusion of ingredients such as probiotics and prebiotics to levels that enable the consumer to derive optimal health benefits . Probiotics are defined as live microorganisms which upon ingestion in adequate numbers impart health benefits to the host animal beyond inherent basic nutrition [4, 9,10]. Most of the probiotic species belong to the genera
2. Fermentation of cereal based foods
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
The quality of some traditional African fermented products (see section 3.2) can be enhanced using beneficial cultures. ‘
Improved production of milk by nursing mothers has been attributed to consumption of fermented
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
2.1.2. Inhibition of pathogenic microorganisms in fermented foods.
Spontaneous fermentation may involve species of
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
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
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
|Bacteriocin||Bacterial Species||Active against|
|Bulgarican||Broad, including G (-).|
|N.N||Broad G (+) incl |
|Nisin||Broad G(+) incl |
|Reuterin||Broad G (+), G (-) and fungi|
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
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
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 .
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
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
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
|LAB isolate||Reduction of TI (mg)||Percent reduction|
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
2.1.5. Reduction, binding or detoxification of mycotoxins in fermented foods
Mycotoxins are secondary metabolites released into cereal grains and legume seeds by species of the genera
Bacterial and fungal (biological) decontamination is one of the mycotoxin-reducing strategies that have been and are being investigated .
|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|
Aflatoxin B1 could not be detected in fermented maize porridge (
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
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.
3. Cereal-based beverages with a probiotic potential
3.1. Selected non-African cereal foods
Most of the commercial products containing probotics and prebiotics available today are dairy-based . Several workers have, however, endeavoured to develop non-dairy, cereal-based probiotic and/or synbiotic products [4, 57, 70-76]. The following non-African fermented cereal beverages have a probiotic potential or in other words, the potential to be transformed into functional beverages.
Spontaneous fermentation involves LAB and yeasts . Lactic acid bacterial species isolated from
The predominant microorganisms in
Pozol is a traditional fermented maize dough consumed in South-eastern Mexico .
3.2. African traditional fermented foods
In Table 5 a number of African traditional lactic acid-fermented cereal-based foods and beverages and the major lactobacilli involved in fermentation are listed. Cereals including maize, sorghum and millet have been used individually or in combination in the preparation of a variety of fermented beverages in Africa .
|Ogi, Ogi-baba||Maize, millet||Paste as staple,||Nigeria,||[11, 26, 99]|
|or sorghum||breakfast or||W. Africa|
|Kwunu-Zaki||Millet,||LAB*||Paste used as||Northern|||
|Mahewu||Maize,||Gritty gruels,||S. Africa||[28, 99]|
|Mawe||Maize||LAB*||Basis of||S. Africa,|||
|or maize plus||Africa|
3.2.6. Mageu (mahewu)
Several studies have been conducted on
This is fermented maize dough consumed in the form of a variety of dishes in Togo, Benin and Nigeria . Making the
3.2.9. Obushera (bushera)
It was observed that use of
3.2.11. Poto poto
This is a traditional fermented maize dough used in homes by the people of the Congo for weaning and for other purposes [86, 100].
When DNA bands from TTGE gels of
This is a non-alcoholic thin porridge drink prepared from sorghum in Malawi and is popularly consumed by people of all demographics in the country. It is important to note however, that there is an alcoholic version of the
Finely ground cereal is slurried with water at a concentration of about 30% w/v. The slurry is spontaneously fermented for two to five days at room temperature (25 C). During fermentation of
|Ethnic group||Local name of product|
4. Microorganisms involved in cereal-based food fermentations
4.1. Lactic acid bacteria (LAB) involved in African food fermentations
Microorganisms of major importance in lactic acid fermentations belong to the genera
|Product name||Dominant bacteria||Reference|
Pediococcus pentosaceus, Lactococcus lactis
Although most of the lactobacilli are generally poor starch fermenters ,
4.2. Other microorganisms and combinations of microbial species involved in cereal based food fermentations
Certain yeasts were important in producing enzymes such as lipase, esterase and phytase . The lipolytic activity resulted in fatty acids which are precursors of flavour while esterase activity determined aroma and flavour. On the other hand, phytase, produced by these organisms, lowers phytic acid which can form complexes with minerals that in turn can negatively affect protein digestibility . A mixture of
4.3. Safety concerns around the use of bacterial strains that could be used as probiotics
The cereal fermented foods and the predominant LAB are generally regarded as safe (GRAS, . Some of the LAB in the fermented food beverages are of human origin and have been used for centuries knowingly or unknowingly . The dominant microorganisms involved in the fermentation of cereal-based beverages have no reported health risk to human life . It was however, noted that some strains of
Most of the bacteria used as probiotics, such as
4.4. Concerns relating to the isomeric type of lactic acid produced by lactic acid bacteria
The organic acids contribute to preservation and food safety, however, it is important to note the concerns relating to L (+) and D (-) lactic acid isomers. The LAB predominantly found in spontaneously fermented African cereal beverages produce lactic acid as one of the major organic acids. Lactic acid contributes to preservation, taste and safety of the fermented foods and beverages . However, lactic acid can occur in two isomers namely L (+) and D (-) isomers and it is only the former isomer that can be degraded in the human system due to the presence of L-lactate dehydrogenase in the gastro-intestinal canal [27, 42, 94]. The genera
5. Probiotic cereal-based beverages
It is estimated that over 60 million people use sorghum and millet as part of their staple food in Africa in the fermented or unfermented form . This is in addition to maize which is a staple cereal for the majority of the people in Africa and elsewhere in the world. This extensive consumption of cereals is partially the basis for the mounting research into the development of non-dairy cereal-based probiotic beverages. Consumers are becoming more aware of the need to eat food for health reasons. This implies that apart from good taste and nutrients provided, food needs to impart additional health benefits to the consumer. Such benefits can be realized by processing the food in such a way that its functionality is improved, for example by incorporating ingredients such as prebiotics and probiotics.
Probiotic bacteria have several reported potential health benefits . Besides probiotics, prebiotic oligosaccharides also impart reported health benefits to the consumer . However, in terms of foods that are used to deliver probiotic bacteria to the consumer, milk and milk products are almost exclusively used for this purpose [4, 10]. Such dairy products however have limitations that include cost (especially in the developing world), allergens, cultural food taboos against milk consumption, requirement of cold-chain facilities, the need to use beverages that form part of the people’s daily diets as well as the need to maintain viability of the probiotic bacterial population in excess of the physiologically required therapeutic minimum of 106 -107 cfu/mL viable cells in the product when consumed .
Probiotic microorganisms need to be consumed regularly and adequately (106 cfu/mL per serving) to maintain the intestinal population and to ensure that health benefits will be derived by the consumer . The increasing need to eat food for health reasons, the demand for vegetarian probiotic foods, the growing lactose intolerance in the world population, and the arguable concern about the cholesterol content of fermented dairy products, are other factors that increase the need for the development of non-dairy cereal-based foods [4, 10, 105]. The following paragraphs illustrate the investigations that have been directed towards cereal- and/or legume-based probiotic beverage development.
5.2. Oats-based probiotic beverages
5.2.3. Other experimental probiotic oats products
Several workers have endeavoured to develop non-dairy cereal-based probiotic food products. An oats-based synbiotic functional drink made by fermenting an oats substrate with
It is important, however, to take the probiotic species into consideration when developing cereal based probiotic beverages. The probiotic bacterial population levels were studied in an envisaged synbiotic oats beverage consisting of 5% oats, 2% inulin, 0.5% whey protein concentrate and 4% sugar . After a storage period of 10 weeks at 4 °C the population levels for two probiotic species (
5.3. Probiotic beverages incorporating malted cereals and hidrolysates
The potential of four bifidobacterial species of human origin to ferment a barley malt hidrolysate similar to that obtained in the brewery was investigated . These species included
In another study relating to barley malt, the potential of using
The factors that influence the growth of selected potential probiotic lactobacilli (e.g.
5.4. Maize (corn)-based probiotic beverages
5.4.1. Synbiotic mahewu (mageu)
The viability of the probiotic strains, in terms of population level, in the fermented synbiotic maize-based beverages at the end of a 90-day storage period at 5 °C exceeded 7.5 log10 cfu/mL . This was well above the recommended therapeutic minimum of 6 log10 cfu/mL at the time of consumption [109, 110]. Intake of a portion of 200 – 300 ml of the experimental synbiotic
5.4.2. Mahewu (mageu) with bifidobacteria
The survival of probiotic
5.4.3. Fermented maize weaning porridge
In a fermented “maize porridge” (18.5% w/w maize meal) mixed with malted barley (1.5% w/w), the growth and metabolism of four strains of probiotic lactobacilli (
5.5. Probiotic soy-based probiotic beverages
Soybeans and rice fermentation media are also reported to be suitable substrates for the growth of certain probiotic lactobacilli and bifidobacteria . Soybean usage is however hampered by the presence of raffinose and stachyose, which can cause flatulence . The non-inactivated lipoxygenase enzyme in the soybean is the causative agent of the beany off-flavour (as perceived in Western societies) in soy-containing products . These limiting factors can, however, be significantly reduced by fermenting with technologically suitable LAB. Soy yoghurt and/or “sogurt” developed using soymilk, is characterized by a hard and coarse texture in addition to a beany “off-flavour”. Coupled with inadequate acid development, this has resulted in a lower sensory appeal of these products . Reports indicate that inclusion of fructose, calcium, cheese whey proteins, gelatin and lactose as well as probiotic bacteria improved the textural and sensory properties of sogurt .
Soymilk is suitable for the growth of lactobacilli and bifidobacteria and a probiotic soymilk and soybean yoghurt with added prebiotic oligofructose and inulin was developed . This was found to be the case with several lactobacilli that included
In summary it can be stated that generally speaking, cereals are good growth-substrates of probiotic bacteria . This is illustrated by the Yosa oats-based product, which to date is the only cereal-based commercial product known to contain both LAB and bifidobacteria. Since cereal-nutrient components vary, growth rates of probiotic organisms may also vary. Further research is therefore imperative to investigate the growth factors that may enhance the growth and survival of lactobacilli and bifidobacteria in cereal-based gruels. The indigestible variable fractions of the cereals can be utilised as prebiotics by probiotics in the GIT of the host upon ingestion of the fermented cereal-based beverage and these should also be defined and tested.
5.6. Therapeutic minimum levels of bacterial species in probiotic beverages
The therapeutic minimum population level for bacterial species in probiotic beverages is recommended to be 106 cfu ml-1. This is the lowest probiotic bacterial count in a probiotic product that may adequately impart prophylactic and therapeutic benefits to the host. In order to realize therapeutic effects of probiotic bacteria in a product, the bacterial counts should exceed 106 cfu ml-1 . Such a dose should be consumed regularly to ensure permanent colonisation in the small intestines. These high bacterial cell counts of probiotic bacteria are proposed to allow for the possible reduction in numbers during passage through the stomach and the intestines . The need to have live probiotic cultures in products claimed to be probiotic has resulted in the formation of regulatory bodies and food legislation in some countries.
The Swiss Food Regulation and the International Standard of FIL/IDF require probiotic products to contain at least 106 cfu ml -1 . The Fermented Milks and Lactic Acid Bacteria Beverages Association of Japan specifies a minimum of 107cfu ml -1 to be present in fresh probiotic dairy products [114, 115]. Japan has the FOSHU (Foods for Specified Health Use) programme for approving functional foods for marketing. A product with a “FOSHU” tag is defined as a food, which is expected to have certain functional benefits and has been licensed to bear a label to that effect . The USA’s National Yoghurt Association (NYA) specifies a population level of 108 cfu/g of lactic acid bacteria, at the time of manufacture, before placing a “Live and Active Culture” logo on the containers of the product . However, in the USA, no indication is given as to what the viable count should be at the end of shelf-life. In the South African context, the South African Food and Health Draft Regulation (regulation 63) stipulates that selected probiotic microbes must be present at levels of at least 106 cfu ml-1 of product in order to exert a beneficial effect .
6. Conclusions and recommendations
Cereals and fermented cereal beverages can be advocated for use as delivery vehicles of health-benefiting functional ingredients such as probiotics and prebiotics. However, it is important to note some of the challenges associated with cereal grains and how they may be circumvented in improving probiotic cereal food delivery to masses in Africa and the developing world. It was noted that there is no known distribution channel for starter cultures to small scale or household scale processers of cereal-based fermented beverages in Africa and the developing world . The other bottleneck is the fact that probiotic strains that have been technologically used successfully in dairy products may not exhibit similar acceptable growth and viability in cereal beverages. This accentuates the need for doing further screening . The developed plant-cereal-based synbiotic beverages may also not have the necessary acceptable sensory attributes [3, 105, 116]. In a recent study, the use of a strain of Lb. paracasei BGP1 in a maize based fermented synbiotic experimental product resulted in off-flavours detected by a trained sensory panel [70, 111].
The use of probiotic strains in a combination of cereals and legumes in fermented products needs to be based on a number of considerations including technological and functional properties; sensory properties, growth rate; capability to deal with antinutritional factors; reduction of toxic substances in cassava; reduction of mycotoxins in cereals; reduction of flatulence causing compounds in legumes; pathogen inhibitory capabilities; co-existence and growth in mixed cultures . These determinations however are hampered by the lack of facilities, expertise and the cost-benefit ratio that, in most cases, is not favourable to small scale and household scale cereal beverage producers in the developing world .