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This article was submitted to Food Microbiology, a section of the journal Frontiers in Microbiology
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A rich variety of indigenous fruits and vegetables grow in Africa, which contribute to the nutrition and health of Africa’s populations. Fruits and vegetables have high moisture and are thus inherently prone to accelerated spoilage. Food fermentation still plays a major role in combating food spoilage and foodborne diseases that are prevalent in many of Africa’s resource disadvantaged regions. Lactic acid fermentation is probably the oldest and best-accepted food processing method among the African people, and is largely a home-based process. Fermentation of leafy vegetables and fruits is, however, underutilized in Africa, although such fermented products could contribute toward improving nutrition and food security in this continent, where many are still malnourished and suffer from hidden hunger. Fermentation of leafy vegetables and fruits may not only improve safety and prolong shelf life, but may also enhance the availability of some trace minerals, vitamins and anti-oxidants. Cassava, cow-peas, amaranth, African nightshade, and spider plant leaves have a potential for fermentation, as do various fruits for the production of vinegars or fruit beers and wines. What is needed to accelerate efforts for production of fermented leaves and vegetables is the development of fermentation protocols, training of personnel and scale-up of production methods. Furthermore, suitable starter cultures need to be developed and produced to guarantee the success of the fermentations.
Statistics show that hunger is still a dramatic problem facing humanity and that nearly 795 million people do not have enough food
Dietary micronutrient deficiencies include calcium, copper, iron, iodine, magnesium, selenium, zinc, and/or vitamin A deficiency (
While the world human population drastically increases, there is a corresponding reduction in availability of land for farming. To worsen this scenario, global warming has a deleterious impact on the agricultural productivity, with dire consequences on the food supply for both developed and developing countries (
Africa is rich in the provision of traditional fermented foods, particularly those based on plant materials as substrates. These are often produced using minimal technology and inputs (
Traditional methods of processing and value addition to vegetables and fruits have a long history throughout Africa (
The aim of this review is to describe different lactic fermented fruit and vegetable fermentations that are currently utilized in Africa and to identify possible novel production processes. The involvement of the different microorganisms associated with the fermentations will be assessed. The beneficial roles that traditional fermented foods may play in the diet and health of African consumers will also be addressed, as well as the development of concepts that could facilitate development of new products or process optimization which may lead to products with improved safety, quality or added value.
Fruits and vegetables produced in the different regions of Africa are classified in this chapter as foods that include leafy vegetables, fruits, and protein-oil seeds. The starchy vegetables are not considered in this review. Very high percentages of fruits and vegetables are consumed after harvest in Africa. In many countries, traditional processing of fruits and vegetables play important roles in the food supply, especially during off seasons and harvest.
Plant products including fruit and vegetables, cereals, legumes, seeds, roots, and tubers are an important source of fiber, carbohydrate, protein (
Proximate composition of some raw leafy African vegetables per 100 g fresh material.
Moisture (g) | Protein (g) | Fat (g) | Total ash (g) | Dietary fiber (g) | Carbohydrates (g) | |
---|---|---|---|---|---|---|
87.3 | 4.24 | 0.12 | 3.23 | |||
89.9 | 3.49 | 0.15 | 2.12 | |||
81 | 5.19 | 0.25 | 3 | |||
89.5 | 0.5 | 0.4 | 1.32 | 2.5 | 8.2 | |
82 | 4.2 | 0.3 | 2.38 | 6.7 | 11.2 | |
79.6 | 3.2 | 0.1 | 1.81 | 10.8 | 15.3 | |
82.4 | 4.7 | 0.6 | 1.76 | 5.8 | 10.5 | |
85.6 | 2.9 | 0.2 | 1.51 | 3 | 9.8 | |
81.3 | 3.5 | 0.4 | 1.66 | 3.8 | 13.1 | |
87.5 | 5 | 0.3 | 1.46 | 3.1 | 5.7 | |
85 | 6 | 0.5 | 4.91 | 2.81 | 6.09 | |
88 | 5 | 0.6 | 2.82 | 2.92 | 3.72 |
Mineral composition of some raw leafy African vegetables per 100 g fresh material.
K (mg) | P (mg) | Ca (mg) | Mg (mg) | Mn (μg) | Fe (mg) | Cu (mg) | Zn (mg) | |
---|---|---|---|---|---|---|---|---|
119 | 383 | 142 | 15.9 | 0.9 | ||||
70.6 | 232 | 141 | 16.2 | 0.8 | ||||
136 | 585 | 80,9 | 6.3 | 0.8 | ||||
257 | 36 | 199 | 92 | 2080 | 7.2 | 0.16 | 0.56 | |
459 | 81 | 443 | 242 | 2340 | 5.1 | 0.17 | 0.7 | |
407 | 118 | 310 | 87 | 790 | 3.6 | 0.19 | 0.57 | |
238 | 51 | 398 | 62 | 2690 | 4.7 | 0.14 | 0.42 | |
351 | 102 | 177 | 67 | 540 | 9.2 | 0.21 | 0.75 | |
260 | 119 | 212 | 59 | 760 | 6.4 | 0.2 | 0.74 | |
374 | 138 | 232 | 76 | 580 | 2.1 | 0.25 | 1.04 | |
106 | 401 | 224 | 4.1 | 4 | 0.3 | 3.1 | ||
60 | 162 | 79 | 2.5 | 2 | 1.2 | 2.6 |
Selected vitamins of some raw leafy African vegetables per 100 g fresh material.
Carotene (mg) | Vitamin A (μg) RAE | Ascorbic acid (mg) | B1 (mg) | B2 (mg) | |
---|---|---|---|---|---|
1.7 | 0.12 | ||||
1.6 | 0.03 | ||||
3.67 | 0.07 | ||||
5.57 | 422 | 5 | 0.08 | 0.17 | |
7.14 | 537 | 2 | 0.04 | 0.05 | |
4.3 | 329 | 1 | 0.02 | 0.03 | |
7.03 | 537 | 9 | 0.07 | 0.08 | |
4.25 | 325 | 2 | 0.04 | 0.1 | |
4.96 | 375 | 10 | 0.01 | 0.1 | |
5.94 | 434 | 2 | 0.06 | 0.21 |
Antioxidants play a role also in the prevention of development of chronic diseases such as cancer, cardio vascular disease (hypertension) and pathogenesis of immune deficiency virus (
Fermentation used as a traditional food processing technique, contributes to human energy food requirement, protein intake, fatty acids, and micronutrient intake. It has been well reported, that especially lactic acid fermentations used as traditional food processing techniques are based on general methods such as mechanical de-hulling of seeds, peeling of tubers, grating, boiling, soaking, and pressing the starting material in order to prepare the substrate for fermentation. This is followed then by the common fermentation stage, where microbial biochemical changes are brought about by wild-type lactic acid bacteria (LAB) that originate from the raw materials (
Cereals (
The tropical climate and agricultural land in Africa supports the growth of different leafy vegetables. Some ALV plants that are traditional to Africa and only successfully grow in this continent are listed in
Distribution of some regional and common African leafy vegetables.
All over the sub-continent | West/East and Central Africa | West and Southern Africa | East/Central and Southern Africa |
---|---|---|---|
In the Congo,
Apart from the effect of lactic preservative influence, reduction of cyanogenic acid in the leaves and mineralization, further beneficial changes are brought about by the fermentation process (
In Kenya, African kale leaves are also processed in a fermentation-like manner, by soaking the vegetables in milk for a few days to achieve the removal of the bitter taste. However, little is known about the fermentation of kale and studies on which bacteria are important for the fermentation and on the dynamics of the fermentation are required.
A significant proportion of the protein intake in African countries is vegetal-plant-protein sources, notably the proteinaceous seeds (oil seeds), many of which are consumed in form of fermented vegetable proteins (
African fermented vegetable proteins with reported microorganisms involved.
Fermented food product | Country | Vegetal Substrate | Microorganisms | Reference |
---|---|---|---|---|
Nigeria | ||||
Nigeria | ||||
Burkina Faso | ||||
Burkina Faso | ||||
Nigeria |
The climatic condition in Africa favors a wide diversity and distribution of plants of the family
Traditional processing of these seeds includes wet de-hulling, boiling and fermentation. There are similar fermented vegetables proteins bearing different names in Africa, also the processing techniques often follow a similar methodology. The common examples of fermented vegetable proteins reported in Africa are shown in
Examples of mixed lactic, acetic acid and alcoholic fermented vegetal starch beverages in Africa.
Fermented food product | Country | Vegetal Substrate | Microorganisms | Reference |
---|---|---|---|---|
Ethiopia | Sorghum | Yeast and LAB | ||
Ethiopia Nigeria, Ghana | Guinea corn and cassava | |||
Nigeria, Ghana | Guinea corn and maize | |||
South Africa | Kaffir corn or maize | |||
East Africa | Maize | |||
Uganda | Maize | Unknown | – | |
Zambia | Maize | Unknown | – | |
Sudan | Sorghum | LAB, yeast | ||
Nigeria (south) | Maize | |||
Egypt | Wheat and maize | Unknown | ||
Egypt | Wheat and milk | |||
Benin | Sorghum | Yeast and LAB |
The ecology of microbes predominantly responsible for the important biochemical changes occurring during traditional fermentation of vegetal proteins was shown to involve diverse bacterial species. Starter cultures are generally not used, and natural fermentation is dominated by different bacteria with enzymatic activities, including
Different fruits are grown in Africa and are harvested annually in different regions of the continent. Fruits used in Africa include banana, papaya,
Examples of mixed lactic, acetic acid and alcoholic fermented fruit beverages in Africa.
Fermented food product | Country | Fruit and vegetable | Fermentation | Microorganisms | Reference |
---|---|---|---|---|---|
Nigeria | Plantain | Alcoholic | |||
Cashew wine | Nigeria | Cashew | Alcoholic | Unknown | – |
Cocoa wine | Nigeria | Cocoa | Alcoholic | Unknown | – |
Palm wine |
Africa | Palm sap | Lactic, later alcoholic and acetic acid | ||
Kenya | Banana | Alcoholic and lactic | Unknown | – | |
East and South Africa | Bamboo | Alcholic and lactic | Unknown | – | |
Kenya | Alcholic and lactic | Uknown | – |
Banana beer is a beverage popular throughout Africa and is made by fermenting banana juice with cereal flour, often sorghum flour (
In Zimbabwe, wild fruits from the buffalo thorn (
In Zimbabwe, an alcoholic beverage called
Recently, a fortified lactic acid fermented probiotic dairy product with a 14% (wt/vol) concentrated baobab fruit pulp,
The fermented juice from palm sap of both
Wine is also produced from the fruits of the
Fruit processing into wine is well developed at an industrial scale in South Africa. Grapes are commonly used for wine production, and LAB play an important role for instance in the malolactic fermentation important for biological de-acidification of wine. This is a decarboxylation process by which malic acid, a dicarboxylic acid naturally present in grape, is converted to lactic acid with concurrent liberation of carbon dioxide. This fermentation plays an important role in de-acidification and aroma development of specific wines. LAB such as
In Africa, different indigenous fruits are also processed into vinegar, however, at a very small scale. Fruit vinegars are made from fruit wines that are processed from fruits such as plum, mango, apple cider,
Fermentation is accompanied by a decomposition of macromolecules. Proteases are active during the alkaline fermentation of vegetable proteins, while amylases and pectinases are important in the macromolecule degradative processes of starchy vegetables. The enzymatic degradative processes result in the breakdown of proteins, carbohydrates and oligosaccharides and thus contribute to the release of important compounds essential to human nutritional requirements (
From a health point of view, African vegetables and fruits contain significant levels of micronutrients, as well as high concentrations of bioactive compounds such as carotenoids, flavonoids, phenolic constituents, alkylresorcinols, glucosinolates and saponins which are present in many fruits and vegetables consumed in Africa and may contribute to the consumer’s health. Furthermore, the dietary fiber and vitamins in African fruits and vegetables, whose levels vary with cultivar, pre- and post-harvesting, processing and storage conditions (
Yeast activity in the fermentation may also increase the vitamin content of vegetables and fruits, such as the availability of riboflavin, vitamin B12 and niacin. Riboflavin and niacin concentrations increased in alcoholic fermented vegetal starch products such as sorghum beer, a popular drink in South Africa, which has been shown to significantly reduce incidences of pellagra (
The multiple problems that are still rampantly occurring on the African continent include problems of infrastructure, water supply, sanitation, and hygiene during processing. These, however, often still compromise the safety and quality of many traditional lactic fermented foods. Home and cottage sized, small-scale food processing endeavors, using crude techniques and rudimentary utensils, are mainly adopted and these are relatively uncontrolled processes, thereby exposing many of these foods to inconsistent quality or to different pathogenic microbes (
Processing using fermentation for value addition to fruits and vegetables is still majorly done in small scale and at household levels. Apart from supporting family nutritional intake, it also contributes to the economic activities, especially by increasing the income of women, who are the major processors and traders. Many of these fermented vegetal foods face safety or quality challenges and the strategies to ameliorate these challenges for sustainable industrial processing is further discussed.
Fermented vegetables and fruit face different microbial deterioration and safety issues. This is mainly a result of contamination during handling or post processing and cross contamination. Inadequate sanitation, inadequate and uninterrupted water supply and lack of good manufacturing practices are challenges to processors in developing countries. As mentioned above, potentially pathogenic bacteria such as
Small scale traditional processing of vegetable and fruits is improving in term of scale-up technology. The processes now utilize specialized, mechanical equipment for grating and milling as well as fermentation tanks, cookers, and hydraulic presses. This has improved processing time and has aided in process scale-up. However, there is still a need for the development of techniques for larger scale industrialization, including peeling and de-hulling systems for seeds and tubers, pressure cookers and boilers, as well as industrial dryers. Optimized packaging and storage of fermented vegetables and fruits may also affect keeping quality and may improve attractiveness. There is ample opportunity for small business development in this sector, but this will depend on a close collaboration of small scale-producers with academic institutions who can provide the training in fermentation technology and who can develop and provide starter cultures. Food microbiologists and food technologists could work hand with women’s groups and local entrepreneurs, while local stakeholders and financial institutions could help to initiate small startup initiatives.
Nutritional value addition to fermented vegetal and fruits would contribute to the dietary status of consumers and thus toward a healthy population, and would also improve product acceptability. Such value addition may arise from the use of multifunctional starter cultures with high potential to increase the bio-availability of especially minerals, different vitamins and antioxidants. Thus, lactic fermentation could play an important role in the improvement of not only shelf life, but also the nutrient availability of fermented vegetal products. An open question which needs to be addressed is that of consumer acceptability of the local population. While lactic fermented foods are common in Africa, the fermentation of leafy vegetables is not common and studies would be required on the sensory acceptability of these products to local consumers.
The research and marketing potential for ALV fermentation should be given high priority. A high variety of indigenous vegetables rich in micronutrients occur in Africa and these should be utilized in order to minimize post-harvest losses. Fermentation is a likely post-harvest processing method that can prevent losses and which contributes to food security and safety. Fermentation of indigenous ALVs with selected starter cultures may lead to improved bio-availability and preservation of trace elements, vitamins and anti-oxidants. Advanced techniques for the production of locally fermented vegetables should be encouraged by local communities, local academic institutions, non-governmental organizations and other stakeholders. Age-old traditions of vegetable fermentation are typical for Europe (e.g.,
In addition, the potential for production of wines and vinegars from fruits should be intensified. Africa has a rich diversity of fruits in its gardens, which could be microbiologically enhanced to high quality vinegars or wines, as to obtain high value products. There certainly could be a good market in Africa or elsewhere for high quality, new juice products and vinegar products for example from indigenous fruits such as cactus pears, marula, Mobola plum (
FO, VF, CF, WH, AG, and HA wrote the main text regarding malnutrition, hidden hunger, and food processing in Africa. G-SC, WB, LF, and BT wrote the parts on nutrition contents and antioxidant activities of the vegetables. BB, JK, HN, NB, and MH wrote the parts on existing fermentations and improving the safety by fermentation, as well as the microbiology of the fermentations.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The responsibility for the article content lies solely with the authors.