- Email: [email protected]
Sorghum and millets: protein sources for Africa
Trends in Food Science & Technology 15 (2004) 94–98
Viewpoint
Sorghum and millets: protein sources for Africa Peter S. Beltona*, John R.N. Taylorb a
School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK (Tel.: +44-1603-593-984; fax: +44-1603-592-003; e-mail: [email protected]) b Department of Food Science, University of Pretoria, 0002 Pretoria, South Africa
pics. Not only are sorghum and millet proteins nutritionally important, they appear to have unique functional characteristics and are potentially the sources of value added products such as biodegradable films. However, they are currently utilised less than optimally and the proteins themselves are relatively under researched compared to those of cereals used in Europe and the North America. The increasing need for an adequate and secure food supply in Africa requires a re-evaluation of these grains and their potential for improved exploitation as sources of energy and protein for the continent. Within this context a European Union funded conference entitled: ‘‘The Proteins of Sorghum and Millets: Enhancing Nutritional and Functional Properties for Africa (AFRIPRO)’’ was held in Pretoria in South Africa in April 2003.1 Representatives from sub Saharan Africa, Europe and the US attended the meeting. The objectives of the conference were: To use the conference to share information, results and ideas. To identify gaps in knowledge and needs and opportunities for new research. To develop proposals for the formation of network of scientists and research programmes between and within Europe and Africa. To identify gaps in knowledge and recommendations for new research.
Sorghum and millets are vitally important cereals for the maintenance of food security in Africa. They represent about half the total cereal production on the continent and as such are a major source of protein for the population. They are still under researched compared to other cereals. This paper reports on a conference recently held in Africa to explore the current state of knowledge on the proteins of these cereals and to suggest routes to the better exploitation for enhanced nutritional and functional properties # 2003 Elsevier Ltd. All rights reserved.
During the conference not only was there a considerable exchange of information and views but delegates reached a common point of view about what were the research needs in sorghums and millets and formulated them as a series of recommendations for action.
Introduction Sorghum, pearl millet and finger millet are indigenous African cereals that, unlike maize and wheat, are well adapted to African semi-arid and sub-tropical agronomic conditions. Some 49 and 55% of world’s millet and sorghum cultivation areas, respectively, are in Africa. These grains represent the major source of dietary energy and protein for some 1 billion people in the semi-arid tro-
The context of sorghum and millets Whilst sorghum which is one species (Sorghum bicolor (L.) Moench) accounts for most of the cultivation of these grains in Africa (Taylor, 2003), a number of millet species are grown. These are (Obilana 2003): Pearl millet—Pennisetum glaucum (L.) R.Br. (accounting for 76% of total production), finger millet—Eleusine 1
* Corresponding author. 0924-2244/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2003.09.002
The entire conference proceedings are available on the web at www.afripro.org.uk or are available on CD from the corresponding author of this article.
P.S. Belton, J.R.N. Taylor / Trends in Food Science & Technology 15 (2004) 94–98
coracana L. Gaertn. (19%), Teff—Eragrostis teff (Zucc.) Trotter (1.8%), and Fonio—Digitaria exilis Stapf. (acha) and Digitaria iburua Stapf. (black fonio) (0.8%). The productivity and cultivation data for sorghum and millets are given in Table 1. Although sorghum and millets account for about the same total production as maize they account for nearly twice the cultivated area. All cereals show low productivities but those for sorghum and millets are very low. Even though total production has been increasing in recent years this has only been achieved by cultivating more and more land. Fig. 1 shows the year on year changes in land cultivated and total sorghum yield (Taylor, 2003). However, where intensive agriculture is practised with improved varieties or hybrids, yields are much higher and comparable with other major cereals, for example in South Africa the average commercial yield in 2001 was 2.34 tonnes/ha compared to 2.49 tonnes/ha for maize. Obviously a continually increasing cultivation area is environmentally highly damaging and in the long-term unsustainable, and efforts must be intensified to improve sorghum agriculture in Africa. Higher yields are essential, not only for rural food security but also for increasing commercialisation. Table 2 gives an analysis of millets and sorghum compared to wheat. Like all cereals they are low in lysine but have protein contents comparable to other cereals and, in the case of some millets, somewhat higher. The storage proteins, which are the main protein Table 1. The areas under cultivation, yield and total production for sorghum, milllets and maize (data Quoted by Rorbach, 2003)
Sorghum Millets Maize
Area (million ha)
Yield (mt/ha)
Production (million mt)
21.8 20.0 21.0
0.8 0.7 1.3
18.1 13.1 27.2
95
components of seeds, are similar in sequence to those of maize (Shewry & Halford, 2003). They consist of three main forms. The alpha form has molecular weights in the range 22,000 and 19,000, and may consist of more than one subgroup. Beta and gamma kafirins, analogous to beta and gamma zeins of maize are present in sorghum, and similar species exist in millets. However the delta zein analogue in sorghum does not contain a methionine rich region but there is some indication that they do exist in millets.
Foods and beverages from sorghum and millets In Africa there is an almost bewildering variety of traditional sorghum and millet food products, including whole grain rice-type products, breads and pancakes, dumplings and couscous, porridges, gruels, non-alcoholic fermented beverages, opaque and cloudy beers (Taylor, 2003). An important characteristic of many of these foods is that they have undergone a lactic acid fermentation or a malting process, or both during their production. These simple technologies improve both the nutritional and functional properties of sorghum and millet. Lactic acid fermentation, using natural mixed cultures comprising mainly mesophilic, heterofermentative lactic acid bacteria, has been shown to improve the digestibility of sorghum proteins, probably through modification of their structure. Additionally, the low pH generated protects these foods against the growth of pathogenic bacteria. This is of great importance in Africa where many people still do not have access to safe water. An example of such a fermented sorghum or millet product is injera, the staple food of Ethiopia. It is a 50 cm diameter pancake with a honeycomb-like texture, rather like a giant crumpet (Fig. 2). Injera is unique in that despite the fact that it is not made from gluten-containing wheat, it is leavened. By cooking part of the dough to gelatinise the starch, the carbon dioxide produced by the fermentation is trapped and leavens the injera on baking as it escapes. Malting (sprouting) improves sorghum and millet protein quality through proteolysis and transamination. Table 2. Major nutrients of millets and sorghum in Africa (adapted from Obilana, 2003)
Fig. 1. The changes in cultivated area (squares) and total yield (circles) of sorghum from 1975 to 2001. The lines are the best fit to a linear model.
Major nutrients Cereal type (quantities are grams of nutrient Pearl Finger Teff millet millet per 100 grams of grain)
Fonio Sorghum Wheat
Protein Carbohydrate Fat Crude fibre Ash Food energy (KJ)
9.0 75.0 1.8 3.3 3.4 1541
11.0 70.0 4.8 2.3 1.9 1483
7.3 74.0 1.3 3.6 2.6 1403
9.6 73.0 2.0 3.0 2.9 1411
7.9 73.0 2.8 2.3 1.6 1142
7.8 71.0 1.1 2.0 1.6 1105
96
P.S. Belton, J.R.N. Taylor / Trends in Food Science & Technology 15 (2004) 94–98
Fig. 2. Removing an injera from the mitad (clay baking griddle).
Protein quantity is also increased as a result of carbohydrate respiration (Dewar, 2003). Alpha-amylase activity during malting also results in modification of the grain starch. Thus porridges made with malted grain have greatly improved carbohydrate digestibility and palatability. The use of malt in porridge making is referred to as Power Flour of Amylase Rich Flour (ARF) technology. Power Flour technology is of particular importance in weaning foods where the energy and nutrient density can be too low, resulting in infant malnutrition. An example of such a sorghum or millet product that combines the benefits of both malting and fermentation in its production is togwa, a Tanzanian thin porridge/gruel which is used as a food for children under five.
Current research Compared to cereals such as wheat, rice and maize, sorghum and millet are very under researched. Full analysis and sequencing of the main storage proteins has yet to be carried out and very little work exists on the functional properties of these proteins. One of the main problems with sorghum is the poor digestibility of its protein. On wet cooking the digestibility drops from a value comparable to other cereals in the raw state to a value significantly less (Duodo, 2003). This is a cause for concern since it means that the full nutritional potential of the protein is not realised. This can be particular problem when sorghum is used as a weaning food, in order to ensure enough protein intake a high solids food is required, however this results in high viscosity and makes the food unpalatable for an infant. One approach to this is to produce an extruded weaning food. This results in lower viscosities for high solids content foods as well as making the product nutritionally improved and palatable (Wambugu, Taylor, & Dewar, 2003).
However there is still lack of a full understanding of the fundamental mechanism of low digestibility in sorghum. The lack of lysine and relative lack of methionine, which are essential amino acids, is a problem with all cereals. One way of addressing this problem is by genetic enhancement. This may be done by the introduction of genes encoding the methionine-rich maize beta-zein and the lysine-rich barley chymotrypsin inhibitor CI-2 proteins. In this way transgenic sorghum plants may be produced which have elevated lysine and methionine contents. (Grootboom & O’Kennedy, 2003). Functional properties of sorghum proteins may be exploited to make bread and related products (Hugo, Rooney, & Taylor, 2003;, Hamaker & Bugu, 2003). They have also been used to make biodegradable films for packaging fruits and nuts (Stading, 2003). The plastics have the advantage that, apart from their biodegradability, they are produced from bran, which is a waste product. Extracting the protein content of this would mean a direct waste reduction of 1500 tons in the dry milling industry of South Africa alone. Further waste streams could be utilized e.g. from the sorghum brewery industry. The overall environmental impact could thus be very positive. Both sorghum and millet suffer something of an image problem in Africa, there often tends to be a preference for maize as the premier crop. Investigations into consumer preferences in Botswana (Kebakile et al., 2003) found that consumers defined quality in terms of colour, texture and taste, and these parameters were linked to sorghum varieties and the type of milling process. Consumers wanted ‘‘modern’’ products formulated from sorghum. Typical products named include bread, biscuits, pasta, ‘‘rice’’, breakfast flakes and fermented beverages (mageu). A possible route to these is suggested by work on pearl millet (Pelembe, Dewar, and Taylor, 2003) where malting may be a simple and readily achievable way of processing that produces a nutritionally enhanced material that could form the basis of a number of processed foods. In general increasing urbanisation is increasing the demand for convenience foods made from traditional produce, however there is a problem in both the consistency and quality of supply to the market, this inhibits investment since inadequate supply of suitable materials means that production capacity runs the risk of being left idle. The solutions to this problem lie less in scientific research than in addressing both physical and economic infrastructural problems.
Recommendations for new research It became clear during the conference that there was research activity both in Europe and Africa that was not being fully utilised because of the lack of effective networking between researchers. If a network were to be
P.S. Belton, J.R.N. Taylor / Trends in Food Science & Technology 15 (2004) 94–98
created the added value of research would be considerably enhanced. Seeking funds for creating such a network is therefore a high priority. However although the network will greatly facilitate exchange of information between scientists further work is needed to communicate results to the user community. This requires the formation of a database on sorghum and millet expertise for relevant stakeholders. Thus the language must be intelligible to real users such as farmers, processors and consumers. One of the problems of crop production and utilization is losses through moulds and in milling. Even though waste materials might be used in other ways, as discussed above, clearly efficient processing is desirable. Since the levels of technology available in Africa are very variable a better route to improved efficiency of milling might be to breed varieties with thinner pericarps. Breeding would also be route to improved mould resistance. However it is important in any breeding programme to recognise that it is the total utility of the crop that matters, thus improvements in any one parameter should not be at the expense of others of importance. Thus improved milling quality would be of no value if it results in poorer pest resistance and improved mould resistance must not be at the expense of milling or sensory quality. From the food production point of view the increasing urbanization of Africa offers considerable opportunity for the development of convenience forms of traditional foods. As has been pointed out above this opportunity does have non-scientific problems associated with it. However there is much research and development to be done especially with regard to nutritionally improved foods which are required for the young, the old and the immuno-compromised. A particular need for improvement of these cereals is in amino acid balance. One route to this might be through genetic enhancement, either by identifying key genes for assisting breeding programmes or through direct genetic manipulation. One particular millet, finger millet, seems to have better amino acid balance and mineral content this may therefore be of significant economic potential and export opportunities, but is very under researched.
Conclusions Sorghum and millets are vital to food security in Africa because of their high levels of adaptation to African conditions. Sorghum and millets play and important role. With proper research they could play a more important role and will offer better long-term security than maize. In order to make the best use of the opportunities offered a programme of research and development is needed. Research and development alone, however, will not solve Africa’s food security problems. Technology needs to be allied to commercial developments As Africa
97
urbanises there is a growing demand for processed, value added, convenience food products that meet the needs of the urban consumer. This is resulting in the development of industries to commercially produce traditional African sorghum and millet foods. The development of the sorghum beer industry in southern Africa is an often-quoted example. More recent examples are the production of instant soy-ogi in Nigeria and fermented pearl millet flour in Namibia. A perhaps even more exciting development is the manufacture of ‘‘western’’ type products using sorghum. Notable examples are the manufacture of malted non-alcoholic beverages in Nigeria, e.g. ‘Milo’ and the brewing of stout and lager beer in Nigeria and also, very recently, in Uganda. The demand for these types of products offers great opportunities for entrepreneurs, but these can only be realised if there is a steady supply of good quality grain and reliable production facilities as well as the necessary scientific and technological infrastructure. These are not easy to achieve in much of Africa and such developments will need careful nurturing. Equally important is stable political and economic environment in which local business can flourish. Provided all these conditions are met sorghum and millets could be major contributors to wealth generation and food security in Africa. Such developments need to clearly address and involve all the stakeholders. Any developments must be sustainable and acceptable socially and culturally by all. This means that solutions cannot be imposed from the outside and it must be recognised that food is not agricultural produce, nor is it even processed produce in packaging, it is something that the consumer either wants, or is prepared, to eat. Research must therefore begin and end with the consumer and must take account of the farmer, the trader, the processor and retailer as well.
Acknowledgements Thanks are due to the European Union for funding the conference under contract number ICA4-CT-200250028.
References Dewar, J. (2003). Influence of malting on sorghum protein quality. http://www.afripro.org.uk/papers/Paper18Dewar.pdf cited 20/05/03. Duodu, K. G., Nunes, A., Delgadillo, I., & Belton, P. S. (2003). Low protein digestibility of cooked sorghum—causes and needs for further research. http://www.afripro.org.uk/papers/ Paper10Duodo.pdf cited 20/05/03. Grootboom, A., & O’Kennedy, M. M. (2003). Genetic enhancement of nutritional quality of grain sorghum. http://www.afripro.org.uk/ papers/Paper06Grootboom.pdf cited 20/05/03 Hamaker, B.R., & Bugu, B.A. (2003). Overview: sorghum proteins and food quality. http://www.afripro.org.uk/papers/Paper08Hamaker.pdf cited 20/05/03 Hugo, L. F., Rooney, L. W., & Taylor, J. R. N. (2003). Bread-making with malted and fermented sorghum. http://www.afripro.org.uk/ papers/Paper19Hugo.pdf cited 20/05/03.
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Kebakile, M. M., Mpotokwane, S. M., Motswagole, B. S., Lima de Faria, M., Santo, P., Domingues, M., & Saraiva, C. (2003). Consumer attitudes to sorghum foods in botswana. http://www.afripro.org.uk/papers/Paper12Kebakile.pdf cited 20/05/03. Obilana, A. B. (2003). Overview: importance of millets in Africa. http://www.afripro.org.uk/papers/Paper02Obilana.pdf cited 20/05/03. Pelembe, L. A. M., Dewar, J., & Taylor, J. R. N. (2003). Food products from malted pearl millet. http://www.afripro.org.uk/papers/ Paper21Pelemebe.pdf cited 20/05/03. Rohrbach, D. D. (2003) ‘Improving the Commercial Viability of Sorghum and Pearl Millet in Africa’ http://www.afripro.org.uk/ papers/Paper22Rohrbach.pdf cited 20/05/03.
Shewry, P. R., & Halford, N. G. (2003). The prolamin storage proteins of sorghum and millets. http://www.afripro.org.uk/papers/ Paper03Shewry.pdf cited 20/05/03. Stading, M. (2003). Environment-friendly packaging solutions for enhanced storage and quality of Southern Africa’s fruit and nut exports : the Enviropak Project. http://www.afripro.org.uk/papers/ Paper05Stading.pdf cited 20/05/03. Taylor, J. R. N. (2003). Overview: importance of sorghum in Africa. http://www.afripro.org.uk/papers/Paper01Taylor.pdf cited 20/05/03. Wambugu, S. M., Taylor, J. R. N., & Dewar, J. (2003). Effect of addition of malted and fermented sorghum flours on proximate composition, viscosity, pH and consumer acceptability of extruded sorghum weaning porridges. http://www.afripro.org.uk/papers/Paper20Wambugu.pdf cited 20/05/03.
Viewpoint
Sorghum and millets: protein sources for Africa Peter S. Beltona*, John R.N. Taylorb a
School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK (Tel.: +44-1603-593-984; fax: +44-1603-592-003; e-mail: [email protected]) b Department of Food Science, University of Pretoria, 0002 Pretoria, South Africa
pics. Not only are sorghum and millet proteins nutritionally important, they appear to have unique functional characteristics and are potentially the sources of value added products such as biodegradable films. However, they are currently utilised less than optimally and the proteins themselves are relatively under researched compared to those of cereals used in Europe and the North America. The increasing need for an adequate and secure food supply in Africa requires a re-evaluation of these grains and their potential for improved exploitation as sources of energy and protein for the continent. Within this context a European Union funded conference entitled: ‘‘The Proteins of Sorghum and Millets: Enhancing Nutritional and Functional Properties for Africa (AFRIPRO)’’ was held in Pretoria in South Africa in April 2003.1 Representatives from sub Saharan Africa, Europe and the US attended the meeting. The objectives of the conference were: To use the conference to share information, results and ideas. To identify gaps in knowledge and needs and opportunities for new research. To develop proposals for the formation of network of scientists and research programmes between and within Europe and Africa. To identify gaps in knowledge and recommendations for new research.
Sorghum and millets are vitally important cereals for the maintenance of food security in Africa. They represent about half the total cereal production on the continent and as such are a major source of protein for the population. They are still under researched compared to other cereals. This paper reports on a conference recently held in Africa to explore the current state of knowledge on the proteins of these cereals and to suggest routes to the better exploitation for enhanced nutritional and functional properties # 2003 Elsevier Ltd. All rights reserved.
During the conference not only was there a considerable exchange of information and views but delegates reached a common point of view about what were the research needs in sorghums and millets and formulated them as a series of recommendations for action.
Introduction Sorghum, pearl millet and finger millet are indigenous African cereals that, unlike maize and wheat, are well adapted to African semi-arid and sub-tropical agronomic conditions. Some 49 and 55% of world’s millet and sorghum cultivation areas, respectively, are in Africa. These grains represent the major source of dietary energy and protein for some 1 billion people in the semi-arid tro-
The context of sorghum and millets Whilst sorghum which is one species (Sorghum bicolor (L.) Moench) accounts for most of the cultivation of these grains in Africa (Taylor, 2003), a number of millet species are grown. These are (Obilana 2003): Pearl millet—Pennisetum glaucum (L.) R.Br. (accounting for 76% of total production), finger millet—Eleusine 1
* Corresponding author. 0924-2244/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2003.09.002
The entire conference proceedings are available on the web at www.afripro.org.uk or are available on CD from the corresponding author of this article.
P.S. Belton, J.R.N. Taylor / Trends in Food Science & Technology 15 (2004) 94–98
coracana L. Gaertn. (19%), Teff—Eragrostis teff (Zucc.) Trotter (1.8%), and Fonio—Digitaria exilis Stapf. (acha) and Digitaria iburua Stapf. (black fonio) (0.8%). The productivity and cultivation data for sorghum and millets are given in Table 1. Although sorghum and millets account for about the same total production as maize they account for nearly twice the cultivated area. All cereals show low productivities but those for sorghum and millets are very low. Even though total production has been increasing in recent years this has only been achieved by cultivating more and more land. Fig. 1 shows the year on year changes in land cultivated and total sorghum yield (Taylor, 2003). However, where intensive agriculture is practised with improved varieties or hybrids, yields are much higher and comparable with other major cereals, for example in South Africa the average commercial yield in 2001 was 2.34 tonnes/ha compared to 2.49 tonnes/ha for maize. Obviously a continually increasing cultivation area is environmentally highly damaging and in the long-term unsustainable, and efforts must be intensified to improve sorghum agriculture in Africa. Higher yields are essential, not only for rural food security but also for increasing commercialisation. Table 2 gives an analysis of millets and sorghum compared to wheat. Like all cereals they are low in lysine but have protein contents comparable to other cereals and, in the case of some millets, somewhat higher. The storage proteins, which are the main protein Table 1. The areas under cultivation, yield and total production for sorghum, milllets and maize (data Quoted by Rorbach, 2003)
Sorghum Millets Maize
Area (million ha)
Yield (mt/ha)
Production (million mt)
21.8 20.0 21.0
0.8 0.7 1.3
18.1 13.1 27.2
95
components of seeds, are similar in sequence to those of maize (Shewry & Halford, 2003). They consist of three main forms. The alpha form has molecular weights in the range 22,000 and 19,000, and may consist of more than one subgroup. Beta and gamma kafirins, analogous to beta and gamma zeins of maize are present in sorghum, and similar species exist in millets. However the delta zein analogue in sorghum does not contain a methionine rich region but there is some indication that they do exist in millets.
Foods and beverages from sorghum and millets In Africa there is an almost bewildering variety of traditional sorghum and millet food products, including whole grain rice-type products, breads and pancakes, dumplings and couscous, porridges, gruels, non-alcoholic fermented beverages, opaque and cloudy beers (Taylor, 2003). An important characteristic of many of these foods is that they have undergone a lactic acid fermentation or a malting process, or both during their production. These simple technologies improve both the nutritional and functional properties of sorghum and millet. Lactic acid fermentation, using natural mixed cultures comprising mainly mesophilic, heterofermentative lactic acid bacteria, has been shown to improve the digestibility of sorghum proteins, probably through modification of their structure. Additionally, the low pH generated protects these foods against the growth of pathogenic bacteria. This is of great importance in Africa where many people still do not have access to safe water. An example of such a fermented sorghum or millet product is injera, the staple food of Ethiopia. It is a 50 cm diameter pancake with a honeycomb-like texture, rather like a giant crumpet (Fig. 2). Injera is unique in that despite the fact that it is not made from gluten-containing wheat, it is leavened. By cooking part of the dough to gelatinise the starch, the carbon dioxide produced by the fermentation is trapped and leavens the injera on baking as it escapes. Malting (sprouting) improves sorghum and millet protein quality through proteolysis and transamination. Table 2. Major nutrients of millets and sorghum in Africa (adapted from Obilana, 2003)
Fig. 1. The changes in cultivated area (squares) and total yield (circles) of sorghum from 1975 to 2001. The lines are the best fit to a linear model.
Major nutrients Cereal type (quantities are grams of nutrient Pearl Finger Teff millet millet per 100 grams of grain)
Fonio Sorghum Wheat
Protein Carbohydrate Fat Crude fibre Ash Food energy (KJ)
9.0 75.0 1.8 3.3 3.4 1541
11.0 70.0 4.8 2.3 1.9 1483
7.3 74.0 1.3 3.6 2.6 1403
9.6 73.0 2.0 3.0 2.9 1411
7.9 73.0 2.8 2.3 1.6 1142
7.8 71.0 1.1 2.0 1.6 1105
96
P.S. Belton, J.R.N. Taylor / Trends in Food Science & Technology 15 (2004) 94–98
Fig. 2. Removing an injera from the mitad (clay baking griddle).
Protein quantity is also increased as a result of carbohydrate respiration (Dewar, 2003). Alpha-amylase activity during malting also results in modification of the grain starch. Thus porridges made with malted grain have greatly improved carbohydrate digestibility and palatability. The use of malt in porridge making is referred to as Power Flour of Amylase Rich Flour (ARF) technology. Power Flour technology is of particular importance in weaning foods where the energy and nutrient density can be too low, resulting in infant malnutrition. An example of such a sorghum or millet product that combines the benefits of both malting and fermentation in its production is togwa, a Tanzanian thin porridge/gruel which is used as a food for children under five.
Current research Compared to cereals such as wheat, rice and maize, sorghum and millet are very under researched. Full analysis and sequencing of the main storage proteins has yet to be carried out and very little work exists on the functional properties of these proteins. One of the main problems with sorghum is the poor digestibility of its protein. On wet cooking the digestibility drops from a value comparable to other cereals in the raw state to a value significantly less (Duodo, 2003). This is a cause for concern since it means that the full nutritional potential of the protein is not realised. This can be particular problem when sorghum is used as a weaning food, in order to ensure enough protein intake a high solids food is required, however this results in high viscosity and makes the food unpalatable for an infant. One approach to this is to produce an extruded weaning food. This results in lower viscosities for high solids content foods as well as making the product nutritionally improved and palatable (Wambugu, Taylor, & Dewar, 2003).
However there is still lack of a full understanding of the fundamental mechanism of low digestibility in sorghum. The lack of lysine and relative lack of methionine, which are essential amino acids, is a problem with all cereals. One way of addressing this problem is by genetic enhancement. This may be done by the introduction of genes encoding the methionine-rich maize beta-zein and the lysine-rich barley chymotrypsin inhibitor CI-2 proteins. In this way transgenic sorghum plants may be produced which have elevated lysine and methionine contents. (Grootboom & O’Kennedy, 2003). Functional properties of sorghum proteins may be exploited to make bread and related products (Hugo, Rooney, & Taylor, 2003;, Hamaker & Bugu, 2003). They have also been used to make biodegradable films for packaging fruits and nuts (Stading, 2003). The plastics have the advantage that, apart from their biodegradability, they are produced from bran, which is a waste product. Extracting the protein content of this would mean a direct waste reduction of 1500 tons in the dry milling industry of South Africa alone. Further waste streams could be utilized e.g. from the sorghum brewery industry. The overall environmental impact could thus be very positive. Both sorghum and millet suffer something of an image problem in Africa, there often tends to be a preference for maize as the premier crop. Investigations into consumer preferences in Botswana (Kebakile et al., 2003) found that consumers defined quality in terms of colour, texture and taste, and these parameters were linked to sorghum varieties and the type of milling process. Consumers wanted ‘‘modern’’ products formulated from sorghum. Typical products named include bread, biscuits, pasta, ‘‘rice’’, breakfast flakes and fermented beverages (mageu). A possible route to these is suggested by work on pearl millet (Pelembe, Dewar, and Taylor, 2003) where malting may be a simple and readily achievable way of processing that produces a nutritionally enhanced material that could form the basis of a number of processed foods. In general increasing urbanisation is increasing the demand for convenience foods made from traditional produce, however there is a problem in both the consistency and quality of supply to the market, this inhibits investment since inadequate supply of suitable materials means that production capacity runs the risk of being left idle. The solutions to this problem lie less in scientific research than in addressing both physical and economic infrastructural problems.
Recommendations for new research It became clear during the conference that there was research activity both in Europe and Africa that was not being fully utilised because of the lack of effective networking between researchers. If a network were to be
P.S. Belton, J.R.N. Taylor / Trends in Food Science & Technology 15 (2004) 94–98
created the added value of research would be considerably enhanced. Seeking funds for creating such a network is therefore a high priority. However although the network will greatly facilitate exchange of information between scientists further work is needed to communicate results to the user community. This requires the formation of a database on sorghum and millet expertise for relevant stakeholders. Thus the language must be intelligible to real users such as farmers, processors and consumers. One of the problems of crop production and utilization is losses through moulds and in milling. Even though waste materials might be used in other ways, as discussed above, clearly efficient processing is desirable. Since the levels of technology available in Africa are very variable a better route to improved efficiency of milling might be to breed varieties with thinner pericarps. Breeding would also be route to improved mould resistance. However it is important in any breeding programme to recognise that it is the total utility of the crop that matters, thus improvements in any one parameter should not be at the expense of others of importance. Thus improved milling quality would be of no value if it results in poorer pest resistance and improved mould resistance must not be at the expense of milling or sensory quality. From the food production point of view the increasing urbanization of Africa offers considerable opportunity for the development of convenience forms of traditional foods. As has been pointed out above this opportunity does have non-scientific problems associated with it. However there is much research and development to be done especially with regard to nutritionally improved foods which are required for the young, the old and the immuno-compromised. A particular need for improvement of these cereals is in amino acid balance. One route to this might be through genetic enhancement, either by identifying key genes for assisting breeding programmes or through direct genetic manipulation. One particular millet, finger millet, seems to have better amino acid balance and mineral content this may therefore be of significant economic potential and export opportunities, but is very under researched.
Conclusions Sorghum and millets are vital to food security in Africa because of their high levels of adaptation to African conditions. Sorghum and millets play and important role. With proper research they could play a more important role and will offer better long-term security than maize. In order to make the best use of the opportunities offered a programme of research and development is needed. Research and development alone, however, will not solve Africa’s food security problems. Technology needs to be allied to commercial developments As Africa
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urbanises there is a growing demand for processed, value added, convenience food products that meet the needs of the urban consumer. This is resulting in the development of industries to commercially produce traditional African sorghum and millet foods. The development of the sorghum beer industry in southern Africa is an often-quoted example. More recent examples are the production of instant soy-ogi in Nigeria and fermented pearl millet flour in Namibia. A perhaps even more exciting development is the manufacture of ‘‘western’’ type products using sorghum. Notable examples are the manufacture of malted non-alcoholic beverages in Nigeria, e.g. ‘Milo’ and the brewing of stout and lager beer in Nigeria and also, very recently, in Uganda. The demand for these types of products offers great opportunities for entrepreneurs, but these can only be realised if there is a steady supply of good quality grain and reliable production facilities as well as the necessary scientific and technological infrastructure. These are not easy to achieve in much of Africa and such developments will need careful nurturing. Equally important is stable political and economic environment in which local business can flourish. Provided all these conditions are met sorghum and millets could be major contributors to wealth generation and food security in Africa. Such developments need to clearly address and involve all the stakeholders. Any developments must be sustainable and acceptable socially and culturally by all. This means that solutions cannot be imposed from the outside and it must be recognised that food is not agricultural produce, nor is it even processed produce in packaging, it is something that the consumer either wants, or is prepared, to eat. Research must therefore begin and end with the consumer and must take account of the farmer, the trader, the processor and retailer as well.
Acknowledgements Thanks are due to the European Union for funding the conference under contract number ICA4-CT-200250028.
References Dewar, J. (2003). Influence of malting on sorghum protein quality. http://www.afripro.org.uk/papers/Paper18Dewar.pdf cited 20/05/03. Duodu, K. G., Nunes, A., Delgadillo, I., & Belton, P. S. (2003). Low protein digestibility of cooked sorghum—causes and needs for further research. http://www.afripro.org.uk/papers/ Paper10Duodo.pdf cited 20/05/03. Grootboom, A., & O’Kennedy, M. M. (2003). Genetic enhancement of nutritional quality of grain sorghum. http://www.afripro.org.uk/ papers/Paper06Grootboom.pdf cited 20/05/03 Hamaker, B.R., & Bugu, B.A. (2003). Overview: sorghum proteins and food quality. http://www.afripro.org.uk/papers/Paper08Hamaker.pdf cited 20/05/03 Hugo, L. F., Rooney, L. W., & Taylor, J. R. N. (2003). Bread-making with malted and fermented sorghum. http://www.afripro.org.uk/ papers/Paper19Hugo.pdf cited 20/05/03.
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Kebakile, M. M., Mpotokwane, S. M., Motswagole, B. S., Lima de Faria, M., Santo, P., Domingues, M., & Saraiva, C. (2003). Consumer attitudes to sorghum foods in botswana. http://www.afripro.org.uk/papers/Paper12Kebakile.pdf cited 20/05/03. Obilana, A. B. (2003). Overview: importance of millets in Africa. http://www.afripro.org.uk/papers/Paper02Obilana.pdf cited 20/05/03. Pelembe, L. A. M., Dewar, J., & Taylor, J. R. N. (2003). Food products from malted pearl millet. http://www.afripro.org.uk/papers/ Paper21Pelemebe.pdf cited 20/05/03. Rohrbach, D. D. (2003) ‘Improving the Commercial Viability of Sorghum and Pearl Millet in Africa’ http://www.afripro.org.uk/ papers/Paper22Rohrbach.pdf cited 20/05/03.
Shewry, P. R., & Halford, N. G. (2003). The prolamin storage proteins of sorghum and millets. http://www.afripro.org.uk/papers/ Paper03Shewry.pdf cited 20/05/03. Stading, M. (2003). Environment-friendly packaging solutions for enhanced storage and quality of Southern Africa’s fruit and nut exports : the Enviropak Project. http://www.afripro.org.uk/papers/ Paper05Stading.pdf cited 20/05/03. Taylor, J. R. N. (2003). Overview: importance of sorghum in Africa. http://www.afripro.org.uk/papers/Paper01Taylor.pdf cited 20/05/03. Wambugu, S. M., Taylor, J. R. N., & Dewar, J. (2003). Effect of addition of malted and fermented sorghum flours on proximate composition, viscosity, pH and consumer acceptability of extruded sorghum weaning porridges. http://www.afripro.org.uk/papers/Paper20Wambugu.pdf cited 20/05/03.