ABSTRACT

Protein digestibility of sorghum is generally low. Malting is one of the processing methods which can be applied to improve this digestibility. It is a method whose technology is well known by local communities in Kenya. The objective of this study was to investigate the effect of malting on the digestibility of some varieties of sorghum grain grown in Kenya. Protein digestibility in the grain and malt was determined using porcine pepsin. In raw unmalted sorghum, the protein digestibility ranged from 0% in the high tannin varieties of Essuti, IS 8613, Nakhadabo and Seredo to 66.4% in the low tannin IESV 91022. Cooking decreased the digestibility of all the sorghum grain whose digestibility was above 0%, mostly the low tannin varieties. When the sorghum grain was malted, the digestibility ranged from a minimum of 45.5% in Essuti to 88.7% in KM 1 in the raw sorghum. In the cooked malted sorghum, the digestibility ranged from 23.7% in Seredo to 100% in the low tannin varieties of KM1, IESV 91022 and KAT 386. There were significant differences (P<0.001) in digestibility due to variety. The protein digestibility of very high tannin sorghum varieties increased with germination period between 72 and 144 hours during malting. Further investigation is required on the mechanisms through which malting influences protein digestibility.

Keywords: sorghum, malting, protein digestibility

L'EFFET DU MALTAGE SUR LA DIGESTIBILITE PROTEINIQUE DE CERTAINES VARIETES DE SORGHO (Sorghum bicolor) CULTIVÉES AU KENYA

RÉSUMÉ

La digestibilité protéinique du sorgho est généralement basse. Le maltage est l'une des méthodes de traitement qui peut être appliquée pour améliorer cette digestibilité. Il s'agit d'une méthode dont la technologie est bien connue par les communautés locales au Kenya. L'objectif de cette étude était de chercher l'effet du maltage sur la digestibilité de certaines variétés de graines de sorgho cultivées au Kenya. La digestibilité protéinique dans la graine et le malt a été déterminée en utilisant la pepsine porcine. Dans du sorgho cru sans malt, la digestibilité protéinique variait de 0% dans les variétés de haut tannin d'Essuti, IS 8613, Nakhadabo et Seredo à 66,4% de bas tannin IESV 91022. La cuisson a diminué la digestibilité de toutes les graines de sorgho dont la digestibilité était au-dessus de 0%, surtout les variétés de bas tannin. Lorsque les graines de sorgho étaient maltées, la digestibilité variait d'un minimum de 45,5% en Essuti à 88,7% en KM 1 dans le sorgho cru. Dans le sorgho cuit et malté, la digestibilité variait de 23,7% en Seredo à 100% dans les variétés de bas tannin de KM1, IESV 91022 et KAT 386. Il y avait de grandes différences (P<0,001) dans la digestibilité selon la variété. La digestibilité protéinique des variétés de sorgho de très haut tannin augmentait avec la période de germination entre 72 et 144 heures pendant le maltage. Des recherches plus approfondies sont nécessaires sur les mécanismes par lesquels le maltage influence la digestibilité protéinique.

Mots clés: sorgho, maltage, digestibilité protéinique.

INTRODUCTION

Digestibility of sorghum protein is of immense interest, particularly to communities in Kenya and elsewhere who depend on sorghum as their staple food. In such situations, the cereal is often also the main source of dietary protein. Of even more importance, sorghum and finger millet porridge is widely used in Kenya as a weaning food for children, where it is again the main source of protein for such children. Improving protein digestibility in such situations is one way of alleviating protein-energy malnutrition, which is relatively high.

Sorghum's protein content is more variable than maize protein and can range from 7 to 15 % [1]. As is the case with other cereals, sorghum protein is generally low in lysine, which is its first limiting amino acid. To be of adequate nutritional quality for human beings, it therefore needs supplementing with lysine. For growing children, it may additionally require supplementation with threonine and methionine [2]. The average protein content of 522 varieties from world sorghum collection was found to be 12.61% [3]. Lysine was the limiting amino acid and its average content was found to be 2.1% of protein [3]. Threonine was found to be the second limiting amino acid [4]. This deficiency in essential amino acids (AA) is not unique to sorghum, but common to all cereals.

Sorghum protein is also unusually high in the nutritionally valueless prolamine [2]. This is an alcohol soluble cross-linked form of protein that humans cannot easily digest. It has been reported that prolamine accounts for 59 % of the total protein in normal sorghum [2]. This is higher than in major cereals, and it considerably lowers the protein digestibility and food value of sorghum considerably.

The protein digestibility of sorghum grain has been reported to be lower than that of other cereals such as maize, rice and wheat [5]. It has also been reported that cooking may further lower the protein digestibility of sorghum grain [6]. Some workers have concluded that the lower digestibility of cooked sorghum was due to the formation during cooking of a starch fraction that is resistant to digestion and to the content of the endosperm protein, kafirin, that binds with tannin [7].

Though differences in protein digestibility between sorghum grain and other cereal grains in man has been evident, it was observed that there was no measurable difference between the digestibility of any of these cereal proteins for laboratory animals such as weanling rats [5]. An in-vitro digestibility method using porcine pepsin was developed that gave results which were more similar to human feeding test results than were those from weanling rats [8].

A few varieties of sorghum that have relatively low prolamine levels have been identified. Some of these are grown in Ethiopia and Sudan. Two varieties found in Ethiopia contained over 30% protein, and had about twice the normal level of lysine [9]. The grains of these sorghum varieties were roasted over a fire, and they were then eaten like peanuts. In Sudan, a remarkable sorghum variety called Karamaka also has high protein content, and its protein is of high nutritional value [1]. Its lysine content is 62 % above that of ordinary sorghum. Its protein has a chemical score of 62 rather than the 30 to 40 figure of regular sorghum protein [3].

The existence of these high protein quality sorghum grain types provides an opportunity of selecting and breeding for this type of grain on a larger scale. There could also be the opportunity of improving the protein content and quality through biotechnology.

The problem of low protein digestibility can, however, be partly solved through processing. Several ways of improving sorghum protein digestibility have been reported [5]. One such method involves cooking sorghum in the presence of an appropriate reducing agent. This method increased protein digestibility by 25% [10]. In contrast, there was no improvement in the digestibility of barley, rice or maize when cooked in this way. The reducing agents found suitable included 2-mercaptoethanol, sodium bisulphite and L-cysteine.

The use of decortication and low cost extrusion processing has also been reported to markedly improve sorghum protein digestibility [11]. Similarly, fermentation also improved the pepsin digestibility of the sorghum protein, though the effect varied with different varieties of sorghum [12]. Unfermented ugali (a thick paste prepared by mixing maize, sorghum, millet or cassava flour in hot water) in East Africa is of comparatively low digestibility [13]. Aliya and Geervani [14] found that the digestibility of fermented sorghum increased significantly, but not that of finger millet or pearl millet. Another report stated that fermentation of sorghum raised its protein digestibility from 59% to 65.5%, while it raised that of pearl millet protein from 74.8% to 85.5% [7].

Malting has been reported to be effective in raising the protein digestibility in sorghum [15]. One simple method practised in Ugandan villages is described by Mukuru [16]. It involves use of equal amounts of clean wood ash and water to make a slurry which is alkaline (pH 11). About one kilogram of grain is mixed with 150 ml of the wood ash slurry in a basket. The basket is then submerged in a well for 12 - 15 hours. Thereafter, the grain is then covered with grass, under which it germinates for 3 - 4 days. When the radicals are 2.5 - 4 cm long, the grain is dried in the sun, then pounded in a traditional way using a mortar and pestle. Winnowing is then used to remove the dry ash and other chaff, while the remaining grain is ground to flour. This flour can be used to make thin porridge or beer. In both products, the tannin level is considerably reduced, and the digestibility increased.

Malt flour with the highest levels of digestibility as measured by soluble nitrogen, soluble sugars and thiamine was obtained from wheat, followed by maize, while sorghum had the lowest digestibility [17]. Dreyer [18], however, reported that malting increased the digestibility of sorghum protein by 7%. There was no comparable improvement shown on malting maize. Effect of malting on sorghum was attributed to the fact that the corneous protein matrix of the endosperm is more effectively digested by the phytoenzyme liberated during the malting than by the enzymes of the gastro-intestinal tract (GIT).

This study aimed at determining the effect of malting on the digestibility of some of the varieties of sorghum grown in Kenya, using the in vitro porcine pepsin method. It also aimed at investigating the effect of germination period during malting on the protein digestibility of high tannin sorghum.

MATERIALS AND METHODS

Samples: Sorghum grain samples, harvested in 1998, were obtained from Kenya Agriculture Research Institute (KARI), Katumani Research Station. Both low and high tannin varieties were selected for digestibility tests. The low tannin sorghum varieties were Kari Mtama 1 (KM 1), Mahube, IESV 91022, KAT 412, KIB 3 and KAT 386. The high tannin sorghum varieties were Essuti, IS 8613, Nakhadabo, Seredo and Red Nyoni. They were kept in a cold room between 5°C and 10°C, to avoid deterioration and insect damage. The grains were cleaned using sieves before malting.

Nitrogen (protein): Determination of nitrogen in the sorghum grain and malt was done using the Kjeldahl method according to the AOAC [19].

Steeping and Malting: Malting of the sorghum grain was done as described by Gomez et al. [20]. About 100 g of sorghum grain of each variety was steeped for 24 hours, then germinated for 96 hours. The germinated grain was dried in an air oven at 50°C for 48 hours. The samples were kept in airtight bottles at between 5°C and 10°C.

Tannin Determination: This was done using the Vanillin Hydrochloric acid method [21,22].

Protein digestibility: This was done using the Porcine pepsin method [7] as adapted by Gomez et al. [20].

The initial protein content of the samples was determined using the micro-Kjeldahl nitrogen determination method [19]. The second stage involved pepsin digestion, where 0.2 g of the sample was weighed in duplicate into centrifuge tubes. To determine the digestibility of a cooked sample, 2 ml of distilled water was added to the sample and shaken, then placed in boiling water for 20 minutes. This step was omitted for determination of protein digestibility of raw samples. To the cooked or raw sample, 20 ml of buffered pepsin solution was added and mixed thoroughly. A blank tube was prepared in a similar manner, but did not contain a sample. The tubes were placed in a water bath at 37°C, and shaken gently every 20 minutes for 2 hours. After this period, the tubes were placed in an ice bath for 30 minutes to attain a temperature of 4°C. The tubes were then centrifuged at 6 000 revolutions per minute (RPM) for 15 minutes. The supernatant was removed with a dropper and discarded. To each tube was added 10 ml of the buffered pepsin solution. It was then well shaken and centrifuged as before. The supernatant was removed and discarded again. Using a spatula, the residue was removed from each tube and placed in the centre of a piece of the filter paper on the Buchner funnel. Suction was applied to the filter flask, and the remaining residue was rinsed from the tube into the funnel using 5 ml of the buffer. The filter papers were rolled and inserted into Kjeldahl flasks. The flasks were dried in the oven for a minimum period of 15 minutes. In the Kjeldahl flask containing the dried filter paper and sample, 10 ml of concentrated H2SO4, 1 g potassium sulphate, and 1 ml of 10% copper sulphate solution were added. Digestion, distillation and titration were done as for the micro-Kjeldahl nitrogen determination. % Protein digestibility was calculated as follows:
(A-B)/A
Where A = % protein in the sample before digestion B = % protein after pepsin digestion.

ANALYSIS OF DATA

Statistical analysis of the data was done to compare the protein digestibility of malted and unmalted sorghum grain. The protein digestibility of the different varieties of sorghum grain was also compared. Differences were considered to be significant between means when the probability that the differences occurred due to chance was less than 0.05 (P<0.05).

RESULTS

Protein Digestibility of Unmalted Sorghum
Protein digestibility in unmalted sorghum grain is presented in Table 1. The digestibility was determined for both raw and cooked samples of 11 sorghum grain varieties. Six of these varieties - Kari Mtama 1 (KM 1), Mahube, IESV 91022, KAT 412, KIB 3 and KAT 386 were low tannin varieties. The other five: Essuti, Seredo, Nakhadabo, IS8613 and Red Nyoni were high tannin varieties.
In both raw and cooked samples, there were significant differences (P <0.001) in protein digestibility among varieties. In the raw sorghum samples, the protein digestibility ranged from a minimum of 0% in the high tannin Essuti, IS 8613, Nakhadabo and Seredo varieties to a maximum of 71.2% in the low tannin KAT 412. All the high tannin samples, with levels of tannin above 2% catechin equivalents (CE), were found to have indigestible protein (protein digestibility of 0%). The observations imply that high tannin content may completely eliminate protein digestibility in unmalted sorghum grain. However, it was observed that Red Nyoni, with a tannin content of 1.3 % CE, had a relatively modest protein digestibility of 35.6%. Among the six low tannin varieties, the protein digestibility ranged from a minimum of 46.6% in Mahube to a maximum of 71.2% in KAT 412. This range is comparable to that observed by other workers such as Ejeta et al. [6], who reported a mean sorghum protein digestibility of 56%.

In the cooked unmalted sorghum samples, the protein digestibility was very much reduced (P<0.001) when compared to that of the raw samples. The mean protein digestibility was 15.4%, and it ranged from a minimum of 0% in the high tannin varieties to 55.7% in IESV 91022.

Protein Digestibility of Malted Sorghum

The protein digestibility of the malted sorghum samples is shown in Table 2. The digestibility of ten malted sorghum grain varieties was determined. Five of these - KM1, KAT 412, Mahube, IESV 91012 and KAT 386- were low tannin varieties. The others; Red Nyoni, Seredo, Nakhadabo, IS 8613 and Essuti were high tannin varieties. The mean digestibility of the raw malted sorghum samples was 65.4%. The digestibility ranged from a minimum of 40.3% in Red Nyoni to a maximum of 88.7% in KM 1. Malting significantly increased (P < 0.001) protein digestibility. The increase was particularly pronounced in the high tannin sorghum varieties of Seredo, Nakhadabo, IS 8613 and Essuti. Each of these had a digestibility of 0% in the unmalted state.

The increase in protein digestibility after malting was even more dramatic in the cooked samples. These had a high mean digestibility of 69.2%. Three samples of the low tannin varieties had 100% digestibility. This implies that for some low tannin sorghum grain varieties, germination for 96 hours during malting may be adequate to obtain optimum protein digestibility. However, other low tannin varieties had relatively low protein digestibility. Mahube, for instance, had a protein digestibility of 33. 6%. It was also observed that for malted samples, cooking increased the digestibility of the other four low tannin varieties except Mahube. This was also true for the high tannin Red Nyoni. This is the reverse of what was observed in the raw samples. However, for the high tannin varieties other than Red Nyoni, cooking resulted in a decrease of protein digestibility.

Effect of Malting on Protein Digestibility of High Tannin Sorghum

The effect of germination period on protein digestibility of high tannin sorghum varieties is shown in Table 3. Three high tannin sorghum varieties were germinated for 72, 96, 120 and 144 hours. Before malting, the protein in all the samples was indigestible. The mean protein digestibility of the raw samples after 72, 96, 120 and 144 hours was 49.7%, 61.1%, 64.0% and 74.8%, respectively. The digestibility increased with germination time. It was also noted that Essuti, with a much higher tannin content than the other varieties, had a lower digestibility at all the germination periods.

The protein digestibility increased from a mean of 42.6% after 72 hours of germination to 60.9% after 144 hours of germination for the cooked samples. The digestibility increased with increasing germination period. However, the rate and extent of the increase between 72 and 144 hours for the cooked samples was much less than that observed in the raw samples. This was particularly true for Nakhadabo, whose protein digestibility increased by 11.7% between the two periods for the cooked sample, while it increased by 20% during the same period for the raw samples.

DISCUSSION

Cooking reduced protein digestibility in the sorghum grain. The reduction in digestibility due to cooking was particularly evident in the low tannin varieties. This indicates that the effect of cooking on reducing protein digestibility is not due to tannins. Bach Knudsen et al. [13] observed that the lower digestibility of cooked sorghum was due to the formation during cooking of a protein-starch fraction that is resistant to digestion, and to the content of the endosperm protein, kafirin, that binds with tannin. It has also been reported that when sorghum is cooked, the solubility of the protein is altered [8]. It was observed that the amount of the soluble kafirins was reduced from 42 to 6%, hence reducing the overall digestibility of sorghum protein [10]. The same researchers also observed that cooking sorghum caused the formation of high molecular weight disulphide linked polymers. These protein polymers formed by cooking may also contribute to limiting the protein digestion.

Sorghum has been reported to have higher levels of cross-linked proteins called kafirins (part of the prolamines) in comparison to other cereals. It has been suggested that these type of proteins are responsible for the low protein digestibility of sorghum following cooking [1]. Sorghum contains about twice the quantity of the indigestible cross-linked kafirin than it does the soluble kafirin protein. This is in contrast with other cereals such as maize and pearl millet which contain more of the soluble kafirin protein than the insoluble fraction [23]. These proteins show only a slight decrease in protein digestibility after cooking.

Ejeta et al. [6] showed that the pepsin test estimated the digestibility of uncooked maize and pearl millet to be similarly high: 82 - 91%. The cooked grain maize and millet showed protein digestibility of 82 - 87%, while that for sorghum was only 56%. However, high lysine sorghum gave digestibility of 73% for the cooked grain. This difference between the two types of sorghum grain implied that the prolamine protein was the main source of protein indigestibility in normal sorghum. These researchers suspected that the problem lay in the formation of protein polymers linked by disulphide bonds.

Malting increased the protein digestibility of both raw and uncooked sorghum grain, though the increase was more pronounced in the cooked grain. The effect of malting on sorghum digestibility has been attributed to the fact that the corneous protein matrix of the endosperm is more effectively digested by enzymes released during malting than by the enzymes of the gastro-intestinal tract [18]. However, the increase in digestibility due to malting observed in these results is much more than the 7% reported by the same researcher. The results are also comparable to those reported by Mosha [15], who worked with two white low tannin and two brown high tannin Tanzanian sorghum varieties. He observed higher in vitro protein digestibility in the raw ungerminated low tannin varieties than in the high tannin varieties. However, in his case malting improved digestibility to a greater extent in the low tannin varieties than it did in the high tannin varieties.

Malting was particularly effective in increasing protein digestibility in the high tannin sorghum varieties. However, the rate and extent of increase differed among the varieties. For Nakhadabo, there was very little increase in protein digestibility of the cooked samples after 96 hours of germination. This indicates that prolonging the germination time beyond 96 hours may not have a significant impact on their digestibility. However, for Essuti the protein digestibility nearly doubled from 26.5% to 50.0 % when the germination period increased from 72 to 144 hours. There was also a steady increase in the digestibility between consecutive germination periods. This implies that for Essuti, it is probable that a significant increase in digestibility may be observed if the germination period is further extended beyond 144 hours.

The observations about the high increase in protein digestibility when high tannin sorghum grain is germinated are similar to those made by Ahmed [24]. This researcher reported that germination reduced the polyphenols and tannins during malting. One explanation for the reduction was that the tannins were released from the complexing moieties of either sugar or polypeptides by the malting process [25].

CONCLUSION

Unmalted sorghum grain varieties had low protein digestibility. Those with tannin levels above 2% CE such as Essuti, IS 8613, Nakhadabo and Seredo had protein digestibility of 0%. Cooking decreased the sorghum digestibility further, particularly for the low tannin varieties. There were differences due to variety in the protein digestibility of sorghum. Malting raised protein digestibility, particularly in the cooked high tannin sorghum varieties. The extent of the increase differed with varieties. It is therefore recommended that consumers use malted sorghum in the preparation of porridge or weaning foods for their children. Further work is required on mechanisms through which malting influences the protein digestibility in sorghum grain, since it was observed that grain with similar tannin levels differed significantly in their protein digestibility.

ACKNOWLEDGEMENT

Financial support for this work was received from the Agricultural Research Fund administered by Kenya Agricultural Research Institute (KARI). We are very grateful for this support. This paper was part of the PhD work for the first author.

REFERENCES

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3. Axtell JD, Oswalt DL, Mertz ET, Pickett RC, Jambunathan R and G Srinivasan Components of nutrition quality in grain sorghum. High Quality Protein Maize. Proceedings of the CIMMYT - Purdue Symposium on Protein Quality in Maize. Dowden, Hutchinson and Ross, Inc. Stroudsburg, USA, 1975;374 - 386.

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5. Axtell JD, Kirleis AW, Hassen MM, Mason ND, Mertz ET and L Munck Digestibility of Sorghum protein. Proceedings of the National Academy of Sciences, USA, 1981;78(3):1333 - 1355.

6. Ejeta G, Mertz ET, Rooney L, Schaffert R and J Yohe (eds) Sorghum Nutritional Quality: Proceedings of an international conference. 26th Feb. - 1st March, 1990. Purdue University, West Lafayette, Indiana, USA, 1990.

7. Bach Knudsen KE, Kirleis AW, Egum BO and L Munck Carbohydrate composition and nutritional quality of sorghum prepared from decorticated white and whole grain red flour for rats. J. Nutr, 1988;118:588 - 597.

8. Mertz ET, Hassan MM, Cairns-Whittern C, Kirleis AW, Lichuan TU and JD Axtell Pepsin digestibility of protein in sorghum and other major cereals. Proceedings of the National Academy of Sciences, USA, 1984;81:1-2.

9. Thorat SS, Satwadhar PN, Kulkarni DN, Choudhar SD and UM Ingle Varietal differences in popping quality of sorghum grains. J. Maharashrta Agr. Sci. 1990;15(2): 173 - 175.

10. Hamaker BR The indigestible sorghum proteins and improvement of digestibility using reducing agents. PhD thesis, Purdue University, West Lafayette, USA, 1986.

11. Maclean WC, de Romana GL, Placko RP and GG Graham Protein quality and digestibility of sorghum in pre-school children: balance studies and plasma free amino acids. J. Nutr. 1981;111:1928-1936.

12. Axtell JD, Ejeta G and L Munck Sorghum Nutritional quality - progress and prospect. In: Sorghum in the Eighties, volume 2. Proceeding of the International Symposium on Sorghum, 2- 7th November 1981, Patancheru, India. International Centre for Research in the Semi - arid Tropics (ICRISAT), 1982;589 - 603.

13. Bach Knudsen KE, Munck L and BO Eggum Effect of cooking, pH and polyphenol level on the carbohydrate composition and nutritional quality of a sorghum food, ugali. Br. J. Nutr. 1988;59:31 - 47.

14. Aliya S and P Geervani An assessment of the protein quality and vitamin B content of commonly used fermented products of legumes and millets. J. Sci. Food Agric. 1981; 32:837 - 842.

15. Mosha AC Nutritional improvement of sorghum by germination technology. In: Food Science and Technology challenges for Africa towards the year 2000 Marovatsanga LT and JRN Taylor ( eds). Proceedings of the ECSAFOST Food Science and Technology Conference, 12 - 16th September, 1994, Victoria Falls, Zimbabwe. University of Zimbabwe, 1994:162 - 174.

16. Mukuru SZ Traditional technologies in small grain processing. Utilization of Sorghum and Millets, Gomez MI, House LR, Rooney LW and DAV Dendy, (eds). ICRISAT, Patancheru, India, 1992;47 - 56.

17. Hussain S, Khan AH, Yasin M, and FH Shah Chemical changes during malting of cereals. Pakistan J. Scient. Ind. Res. 1966;9:137 - 139.

18. Dreyer JJ Biological assessment of protein quality: digestibility of protein in certain foodstuffs. S. Afr. Med. J. 1968;42:1304 - 1313.

19. AOAC. (Association of Official Analytical Chemists). Official Methods of Analysis of the Association of Official Analytical Chemists, 14th edition, 1984. Washington DC, USA.

20. Gomez MI, Obilana AB, Martin DF, Madhvamuse M and ES Monyo Manual of laboratory procedures for quality evaluation of sorghum and pearl millet. Technical Manual No.2, 1997. Patancheru, Andhra Pradesh, India.

21. Burns RE Methods of Tannin Analysis for Forage Crop Evaluation. Georgia Agricultural Experiment Station Technical Bulletin, 1963;32:1-14.

22. Price ML, Van Scoyoc S and LG Butler A critical evaluation of the vanillin reaction as an assay for tannins in sorghum grain. J. Agric. Food Chem., 1978;26:1214-1218.

23. Mertz ET, Axtell JD, Ejeta G and BR Hamaker Development and recent impact of quality protein in maize and sorghum. Cereal Science and Technology: Impact on a changing Africa (Taylor JRN, Randall PG and JH Viljoen (eds). CSIR, South Africa. 1993:115 - 131.

24. Ahmed SB Tannin content, amylase activity and cyanide content of germinated sorghum grain. MSc Thesis, 1988. University of Khartoum, Sudan.

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Table 1
Protein Digestibility (PD) of raw and cooked unmalted sorghum grain

Variety	Protein (%)	Tannins (CE)	PD (%) Raw	PD (%) Cooked
KM1 Mahube IESV 91022 KAT 412 KIB3 KAT 386 Red Nyoni Seredo Nakhadabo IS 8613 Essuti Mean	11.5b 11.3ab 12.2b 13.2b 8.8ab 10.0ab 12.4b 6.5a 14.6b 14.2b 8.9ab 11.2+2.4	0.0L 0.0L 0.0L 0.0L 0.1L 0.2L 1.3H 2.3H 3.8H 5.4H 13.8H	53.9ab 46.9ab 66.4b 71.2b 63.6b 62.0b 35.6ab 0.0a 0.0a 0.0a 0.0a 36.3+29.0	6.0a 23.9ab 55.7b 26.5ab 13.6ab 4.0a 9.3a 0.0a 0.0a 0.0a 0.0a 12.6+16.3

 

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Dr. Wilna Oldewage-Theron

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ABSTRACT

Iron deficiency anaemia, one of the most prevalent problems of micronutrient malnutrition, occurs in many developing countries. Causes of the problem are many, but one of the major causes is low bioavailability of food iron. An increase in the supply of absorbable iron-rich food in the diet should decrease the prevalence of iron deficiency anaemia. One of the strategies to overcome the high prevalence of iron deficiency anaemia in developing countries is to fortify food products with iron, with the goal of increasing the level of iron consumption resulting in improved nutritional status. Food fortification is the most cost effective, sustainable and optimal approach in the battle against iron deficiencies in developing countries. Iron fortification does not have the gastro-intestinal side effects that iron supplements often induce. Fortification iron can be divided into two main forms namely haem iron and non-haem iron. Non-haem iron is more often used for fortification purposes because of availability of and lower cost. Most iron-fortified foods contain potential absorption inhibitors, for example, phytates, polyphenols containing galloyl groups, oxalates and calcium. It is essential to prevent the fortification iron from reacting with the absorption inhibitors. To ensure adequate absorption therefore, various factors must be considered before initiating a fortification programme. These include cost effectiveness of fortification in increasing absorbable iron, palatability of the fortified food and the etiology of iron deficiency. It is thus important to carefully select the food vehicles to be fortified as well as the iron fortificants to be added. A successful iron fortification program depends heavily upon the absorption of the added iron and its protection from some absorptive inhibitors. This paper focuses on the latest technical advancement ruling the selection of food vehicles and iron fortification compounds with the aim of ensuring adequate absorption of fortified iron. The optimization of the iron fortification compounds with the highest potential absorption causing the least subsequent organoleptic problems in the food vehicles is first discussed, followed by a description of ways of protecting and enhancing the absorption of fortification iron, such as applications of acidifiers, haemoglobin, sodium iron ethylene diamine tetra-acetate and amino acid-chelated iron. Finally, the major foods that are used as iron fortification vehicles in South Africa are discussed.

Key words: iron deficiency, anaemia, iron fortificants, food fortification, micronutrient deficiencies

FORTIFICATION DES ALIMENTS POUR PREVENIR ET REDUIRE LES INSUFFISANCES DU FER

RÉSUMÉ

L'anémie causée par l'insuffisance du fer, l'un des problèmes les plus fréquents de la malnutrition liée aux micro-nutriments, se produit dans beaucoup de pays en développement. Les causes de ce problème sont nombreuses, mais l'une des causes majeures est le niveau bas de la disponibilité biologique du fer dans les aliments. Une augmentation dans l'approvisionnement d'aliments riches en fer absorbable dans le régime alimentaire devrait faire baisser la prévalence de l'anémie causée par l'insuffisance du fer. L'une des stratégies visant à réduire la prévalence élevée de l'anémie causée par l'insuffisance du fer dans les pays en développement est de fortifier les produits alimentaires avec du fer, dans le but d'augmenter le niveau de la consommation du fer et, de ce fait, l'état nutritionnel sera amélioré. La fortification des aliments est l'approche la plus rentable, viable et optimale dans la lutte contre l'insuffisance du fer dans les pays en développement. La fortification du fer n'a pas les effets secondaires gastro-intestinaux que les suppléments de fer provoquent souvent. La fortification du fer peut être divisée en deux grandes formes, à savoir le fer avec haem et le fer sans haem. Le fer sans haem est plus souvent utilisé dans le processus de fortification à cause de la disponibilité des ressources et du coût abordable. Comme la plupart des aliments fortifiés avec du fer contiennent des inhibiteurs possibles de l'absorption, par exemple, la présence des phytates, des poly-phénols contenant des groupes de galloyl, les oxalates et le calcium affectent négativement la bio-disponibilité des fortifiants du fer sans haem, il est essentiel d'empêcher au fer de fortification de réagir avec les inhibiteurs de l'absorption en vue d'assurer une absorption adéquate. De nombreux facteurs doivent être pris en considération avant d'initier un programme de fortification. Ces facteurs sont notamment la rentabilité de la fortification en augmentant le fer absorbable, le goût agréable des aliments fortifiés et l'étiologie de l'insuffisance du fer. Il est donc important de sélectionner attentivement les véhicules alimentaires qu'il faut fortifier ainsi que les fortifiants de fer qu'il faut ajouter. Un programme efficace de fortification de fer dépend étroitement de l'absorption du fer ajouté et de sa protection contre certains inhibiteurs de l'absorption. Ce document est axé sur le progrès technique le plus récent qui oriente la sélection des véhicules alimentaires et les composés de la fortification du fer dans le but d'assurer une absorption adéquate du fer fortifié. L'optimisation des composés de la fortification du fer avec le degré le plus élevé d'une éventuelle absorption qui cause le moins de problèmes organoleptiques ultérieurs dans les véhicules alimentaires est analysée en premier lieu, suivie d'une description des moyens de protéger et d'accroître l'absorption du fer de fortification, tels que les applications d'acidifiants, l'hémoglobine, le Tétra-acétate de diamine d'éthylène de fer et de sodium ainsi que le fer amino-acide-chélaté. Enfin, les principaux aliments qui sont utilisés comme véhicules de fortification du fer en Afrique du Sud sont passés en revue.

Mots clés: insuffisance en fer, anémie, fortifiants du fer, fortification des aliments, insuffisances en micro-nutriments

INTRODUCTION

At the International Conference on Nutrition that was sponsored by the Food and Agriculture Organization (FAO) and World Health Organization (WHO) in Rome during 1992, 160 heads of state and government established global goals for the virtual elimination of vitamin A deficiency (VAD) and iodine deficiency disorders (IDD), as well as the reduction of iron deficiency anaemia (IDA) by one third before the end of 2000. Since then, outstanding progress has been made toward the elimination of iodine deficiency through universal salt iodisation. Vitamin A deficiency is being addressed through food diversification, supplementation programmes and fortification of foods. Iron deficiency anamia is, however, the most prevalent of the three deficiencies and affects about one-third of the world's population [1], but too little progress has been made toward the global elimination of iron deficiency (ID) and IDA control has thus been the least successful during this same period. The reasons for this lack of action may be that IDA has few overt symptoms, coupled with a general lack of knowledge of the serious and often permanent consequences to the cognitive development of young children and the negative impact on health.

The global prevalence of ID is estimated at 3.5-5 billion people, 2.2 billion people with IDD and 140-250 million deficient in vitamin A [2]. In Africa, 59.4 million women aged between 15 and 49 years are affected. Anaemia is so pervasive in the developing world, and its intergenerational effects so devastating, that there need be no further justification for concerted action now. The consequences associated with anaemia include debilitating fatigue, compromised immune function, widespread maternal death in childbirth, damage to the foetal brain, premature delivery, intrauterine growth retardation, raised perinatal mortality, and the failure of the child to grow well and develop physically and mentally.

Fortification, one of the strategies to address IDA, is the addition of vitamins and/or minerals to a vehicle with the goal of increasing the nutritional content. Clear evidence exists that fortification is the most cost effective and sustainable strategy in the battle against micronutrient deficiencies, and iron fortification the optimal approach for reducing ID in developing countries [3]. An advantage of iron fortification is that it does not have the gastro-intestinal side effects that iron supplements often induce. The current incidence of IDA in fertile US women is reported at 2.9 % and could be the result of consumption of iron-fortified foods in the United States [3] as the fortification of products such as white bread, rolls, crackers, fish sauce, corn flour, corn grits, pasta and breakfast cereals is widespread, and about 20 % of the total iron intake could be from the fortified iron in these products [4].

Although pilot fortification trials in the developed world reported positive and promising results, no major success examples in the developing world have been reported to date, except perhaps for Chile [5,6]. The reasons could be a lack of political commitment, insufficient funding, not enough technical support from research institutions or industries, poor distribution networks or lack of nutrition education programs for the consumers, all of which are considered necessary for a successful fortification program. Another reason could be poverty resulting in a lack of purchasing power to afford foods containing haem iron. Other contributing factors could be lack of money to afford antenatal services, poor access to health services, inadequate water supply, poor sanitation. All these factors coexist in poor households living in marginalised environments where anaemia rates are reported to be most prevalent [7]. The poor social status of people is another relevant basic cause. At more immediate levels, low iron intake, poor bioavailability of dietary iron, VAD and infections (cholera, Congo fever and parasitic infestation) combine in jeopardising an individual's iron status [8]. However, should low bioavailability of food iron be the major determinant of IDA in the developing world, an increase in the supply of absorbable food iron should decrease the prevalence of IDA.

It is thus important to carefully select the food vehicles to be fortified as well as the iron fortificants to be added. The iron fortificant should, however, be optimised with respect to relative bioavailability before it is added to the food vehicle. It is also true that if potential absorption inhibitors are present in the food vehicle, the added and native iron, will be poorly absorbed, and thus there will be little or even no impact on the consumers' iron status. A successful iron fortification program thus depends heavily upon the absorption of the added iron and its protection from some absorptive inhibitors.

This paper will focus on the technical advancement ruling the selection of food vehicles and iron fortification compounds with the aim of ensuring an adequate absorption of fortified iron. The optimisation of the iron fortification compounds in relation to bioavailability and organoleptic problems will first be discussed, followed by a description of protective methods that can be used to protect the fortified iron from absorptive inhibitors. Finally, the major foods that are used as iron fortification vehicles in South Africa (SA) are discussed.

OPTIMIZATION OF THE IRON FORTIFICATION COMPOUNDS

Features of the most commonly used iron fortificants are shown in Table 1 [3,9]. Iron fortificants are usually classified according to solubility, namely those that are (a) water-soluble; (b) poorly water soluble but soluble in dilute acids; (c) water-insoluble but poorly soluble in dilute acids; and (d) protected iron compounds. In general, the more soluble in water or gastric juice, the higher the bioavailability of the iron fortificant. Fortificants poorly soluble in diluted acids have a low to moderate bioavailability due to the variable dissolution in gastric juice owing to both the characteristics of the fortificant and the meal composition.

Although it would be argued to use the most bioavailable iron fortificants, these fortificants often cause unacceptable flavours and colours in many food vehicles. Optimisation is, therefore, choosing an iron fortificant with the highest potential absorption causing the least subsequent organoleptic problems in the food vehicles.

Bioavailability

During the past 35 years considerable progress has been made in understanding iron absorption by employing iron radioisotopes in human and animal subjects or by in vitro assay. The isotopes, initially incorporated into vegetables were studied by hydroponic methods whereas biosynthetic techniques were applied for animal foods. Considerable absorption variations in the different food items were observed. Iron derived from animal tissue was generally better absorbed than iron from vegetables. Studies also showed that in meals containing two food items, labelled with separate iron isotopes, the absorption of iron from each food item was modified by the other [10]. This led to the important discovery that overall meal composition determines bioavailability and that it is not a unique property of the food source in most circumstances. Further studies refined the current concept of the behaviour of iron destined for absorption in the lumen of the upper small bowel prior to its entrance into mucosal cells [11]. Studies also demonstrated that the measurement of dialysable iron in vitro is a good predictor of iron bioavailability in humans [12]. The relative bioavailability (RBV) of many commercially available iron fortificants is well known (Table 1). Animal or in vitro assays can be used for screening new iron compounds, although human studies are ultimately necessary.

Fortification iron absorption depends primarily on its solubility in gastric juice. Water-soluble fortificants, such as ferrous sulphate, dissolve instantaneously in gastric juice. The absorption of the insoluble or poorly soluble iron fortificants can be improved by reducing particle size, but this is accompanied by an increased reactivity in deteriorative processes. Once dissolved, however, fortification iron enters the common pool, where its absorption (like that of all pool iron) depends on the content of enhancing (such as vitamin C) or inhibitory ligands (such as phytates and polyphenols) in the meal. Iron status is also a determining factor of iron absorption as a satisfactory iron status will diminish and a low iron status will enhance absorption.

Organoleptic problems

Although discolouration and off-flavour development are some of the most frequent problems encountered when adding iron fortificants to food, appearance of specks, segregation, sedimentation, sandy texture, lipid oxidation and vitamin degradation may also occur. Many iron fortificants are coloured and this colour is often a critical factor when fortifying lightly coloured foods. The use of soluble iron fortification compounds often results in changes in colour and flavour due to reactions with other components in the food, but it has the advantage of being highly bioavailable.

Iron fortificants may cause a metallic flavour, especially in liquid products. A change in flavour is mostly the result of lipid oxidation catalysed by iron. Pentane formation can be measured in the headspace of sealed cans, containing iron-fortified products, to determine the potential ability of the iron fortificant to promote fat oxidation in cereals [13]. By coating the fortificant with hydrogenated oils or ethyl cellulose, some of the undesirable interactions with the food matrix can be avoided [14].

Water-soluble fortificants

Water-soluble iron fortificants are the most bioavailable. Ferrous sulphate is usually the relative standard of bioavailability for other iron fortificants. This group of fortificants is, unfortunately, also the most chemically reactive and likely to promote unacceptable colour and flavour changes. Desiccated ferrous sulphate is the cheapest fortificant, mostly used to fortify infant formulae and low acid foods, such as pasta, cereal flour and bread that are stored for only short periods. Colour changes can be prevented if the food is slightly acid because ferrous sulphate turns food brown above pH 6.3. Other possibilities are ferrous gluconate, ferric saccharate, ferric ammonium citrate, ferric glycerophosphate, and ferrous lactate. Ferrous lactate is highly hygroscopic and can, therefore, not be used in dry foods. It is the preferred iron source for liquid foods such as UHT (ultraheat treat) milk and liquid formulae diets [15].

Compounds poorly soluble in water, but soluble in dilute acids

Ferrous citrate, ferrous fumarate, ferrous tartrate and ferrous succinate form part of this group and cause fewer organoleptic problems than water-soluble fortificants and readily enter the common iron pool during digestion. These are mostly used in infant cereals [13] and chocolate drink powder [16].

Extensive tests have shown that ferrous fumarate is suitable for fortification of cereal-based weaning foods, biscuits, and wafers, but because of its brown colour and insolubility, it is not appropriate for fortification of milk and white or off-white foods [17,18].

Compounds water-insoluble and poorly soluble in dilute acids

Water-insoluble, but poorly soluble in dilute acids fortificants include ferric orthophosphate, ferric pyrophosphate, and reduced elemental iron. These are the most often-used compounds in food fortification as no organoleptic problems are caused. A disadvantage, however, is that these fortificants have a variable absorption because of the poor gastric juice solubility. Animal studies indicated that commercial compounds have 50 % absorption compared to ferrous sulphate [13]. Human studies, however, have given variable and conflicting results (Table 1). This could be due to different physiochemical characteristics in the compounds tested, or the influence of different meals on the dissolution of the compounds in gastric juice are different.

Reduced iron is used to fortify wheat and added to flour and ready-to-eat cereals in combination with vitamin B1, B2, B6, and niacin. The amount of reduced iron actually absorbed from fortified flour depends on the diet composition [19,20]. However, ferric pyrophosphate interacts the least with food components, and has a good bioavailability. It can be dispersed and suspended in a liquid food and is used to fortify cereals, pasta products, milk powder, liquid diets, infant formulae and cocoa drinks.

Microencapsulated iron compounds

New micro-encapsulation technologies render iron fortificants that are more resistant to interaction with other components in the food vehicles, thus minimising organoleptic changes, increasing shelf-life and maximising consumer acceptance. Most of the iron compounds can be micro-encapsulated, but the most available products are the microencapsulated form of both ferrous sulphate and ferrous fumarate. The coatings are usually a mixture of phospholipid, polysaccharides, protein or partially hydrogenated oils. Figure 1 is a schematic view of micro-encapsulation. Micro-encapsulation has little influence on RBV [21], and the main advantages are that few organoleptic changes are caused and a prolonged shelf life of fortified foods. This is a result of the bilayer coating, protecting against the interaction between iron and absorption factors in the fortified foods [22].

Fig. 1: A longitudinal view of microencapsulation

PROTECTING AND ENHANCING THE ABSORPTION OF FORTIFICATION IRON

Food iron exists in two main forms, namely haem iron found in meat as part of haemoglobin and myoglobin, and non-haem iron naturally present in cereals, vegetables and other foods. Haem and non-haem iron are absorbed by different pathways with different degrees of efficiency depending on the chemical form, other dietary constituents and the level of iron stores in the individual. Between 20 % and 30 % of haem iron is absorbed and this is a constant figure, being relatively unaffected by other dietary or physiological variables such as body iron stores [23]. A large number of dietary variables that enhance or inhibit non-haem iron absorption have been identified, however [24]. These include chemical reactions in the digestion, such as chelation and changes in iron valency, effects on intestinal or mucosal function, and competition with other minerals for transport protein. The presence of phytates, polyphenols containing galloyl groups, oxalates and calcium are known to adversely affect the bioavailability of non-haem iron fortificants. Their inhibitory effect is usually due to the formation of large insoluble polymers. Many food vehicles for iron fortification contain some substances that inhibit iron absorption. For example, cereals contain polyphenols and phytic acid, milk contains calcium and casein, while coffee, cocoa and tea drinks contain polyphenols. In addition, many diets in developing countries to which fortified salt, sugar or other condiments are added, often have high levels of phytate, oxalic acid and polyphenols from cereal and legume foods. To ensure a high enough level of absorption to improve or maintain iron status, it is necessary to prevent the fortification iron from reacting with the absorption inhibitors.

Acidifier

Acidification of foods represents an important strategy to increase iron bioavailability. Organic acids, such as ascorbic, citric, malic, tartaric and lactic acid form soluble complexes with iron, thus preventing precipitation or polymerisation and thus promoting iron absorption [19,25]. Ascorbic acid is the most common organic acid enhancer, increasing the absorption of both native iron and fortification iron several fold when added to foods. Its effect appears to be related to its ligand action and reducing power. It can change the valency of iron from Fe3+ to Fe2+ and/or maintain Fe2+ in the ferrous state and thus prevent or decrease the formation of insoluble complexes with absorption inhibitors or with hydroxide ion in the gut. In addition, it can form soluble complexes with iron at low pH that remain soluble and absorbable at more alkaline duodenal pH.

Research conducted in Chile showed that the prevalence of anaemia in children between 3 and 15 months old fed iron-fortified milk was reduced from 36 % to 13 %. In children fed with both iron- and vitamin C-fortified milk, anaemia prevalence was reduced from 28 % to 2 %. The data (Figure 2) confirmed that vitamin C and iron together were more effective in reducing anaemia than iron fortification alone [26]. Hallberg et al [20] studied the inhibitory effect of phytate on iron absorption from bread rolls. Increasing the amount of phytate in bread rolls decreased the ratio of iron absorbed from 80 % to 20 %. The inhibitory effect of phytate (25 mg) was neutralised by taking 100 milligram (mg) vitamin C in a beverage with the bread roll.

Figure 2: Prevalence of anemia in children aged 3 to 15 months fed on iron and
iron/vitamin C-fortified milk

Haemoglobin

Haemoglobin (Hb) is a form of food iron that is naturally protected from major iron absorption inhibitors such as phytic acid and polyphenols. The iron is contained within the porphyrin ring of the haem molecule, which is split from the globin moiety during digestion, and is taken up intact into the mucosal cells. The iron is released within the mucosal cell by the action of haem oxygenase and is prevented from reacting with the inhibitory and enhancing ligands within the intestinal lumen.

Haemoglobin is added in the form of dried red blood cells when used as a food additive and its main advantage is a relatively high and predictable iron absorption. Although the absorption varies little with the composition of a meal and to some extent with the iron status of the subject, this variation is less than with non-haem iron [27]. In Latin American countries where the supply of animal blood is plentiful, two field trials demonstrated the potential usefulness of dried red blood cells as an iron fortificant. In the first study with 1000 participants [6], three 10 g wheat flour biscuits containing 6 % bovine Hb concentrate were consumed as part of the Chilean school lunch program over a period of three years. The prevalence of anaemia in 10-16 year old girls decreased from 1.3 % to 0.5 %, and in boys from 0.8 % to 0.4 %. In another study [28], 30 gram (g) extruded rice, containing 5 % bovine Hb concentrate, was fed to infants, 4-12 months old (experimental group). Their iron status was compared with those of infants fed on regular solid foods such as vegetables and meat (control group). In the control group after 12 months, the prevalence of IDA was 17 % compared with 6 % in the experimental group.

The main disadvantage of Hb iron is the low iron content (Table 1) and the intense red-brown colour. Other disadvantages are the difficulties in collecting, drying and storing animal blood, especially in countries where meat is not widely consumed or when religious beliefs forbid the consumption of blood.

Sodium iron ethylene diamine tetra-acetate

Ethylene diamine tetra-acetic acid (EDTA) is a hexadentate chelate compound with four negatively charged carboxylic acid groups and two amine groups. It can combine with virtually every metal ion in the periodic table. Sodium iron ethylene diamine tetra-acetate (NaFeEDTA) is one of many EDTA-chelated compounds. The International Nutritional Anaemia Consultative Group (INACG) recommends NaFeEDTA as a suitable iron fortificant for developing countries [29]. Clinical trials in Guatemala, Venezuela, Thailand and South Africa demonstrated that NaFeEDTA fortification could successfully reduce IDA [30-32].
Advantages of NaFeEDTA include:

- promoting the absorption of intrinsic food iron in a meal with low iron bioavailability;
- providing a highly bioavailable form of iron compound;
- stability;
- bioavailability of iron not affected by adverse storage conditions or by food preparations such as cooking; and
- fewer undesirable characteristics such as rancidity and organoleptic problems than other water-soluble fortificants.

It is, however, not suitable to fortify all staple foods with NaFeEDTA as unwanted colour changes may be caused. Sugar fortified with NaFeEDTA is slightly yellow in colour and when added to tea and coffee, resulted in black tea and deep blue coffee. Similarly, when added to maize starch puddings and gruels, a pinkish-violet colour is the result [33]. In long-term trials conducted in Guatemala, sugar was fortified with NaFeEDTA and consumed for a four-year period [34]. NaFeEDTA was apparently partly hydrolysed in the gut with subsequent partial absorption of the EDTA. Since free EDTA binds divalent cations in the body and is itself not metabolised, there was an increase in urinary excretion of zinc, copper and iron [34]. These results thus indicated a limited use of NaFeEDTA as iron fortificant.

Amino acid-chelated iron

As a solution to the co-chelation problems of NaFeEDTA, different iron chelates were developed using amino acid as ligands. Amino acid chelates could be absorbed like a peptide in the jejunum rather than as non-haem iron in the duodenum. This alternative mechanism has raised concern about the role of iron stores in iron absorption regulation from the amino-chelate.

Ferrous bis-glycinate is formed by two glycine molecules bound to a ferrous cation, resulting in a double heterocyclic ring compound. The carboxyl group of glycine is linked with iron by an ionic bond, whereas the -amino group is joined with the metal by a coordinate covalent bond. The structure shown in Figure 3 was elucidated by X-ray diffraction and infrared spectrometry in which the metal was complexed by two bidentate glycine ligands with a nitrogen atom and a an oxygen atom of each glycine unit acting as donor atoms. It has been proposed that this configuration protects the iron from dietary inhibitors and intestinal interactions [35].

Figure 3: Molecular structure diagram for ferrous bis-glycinate



Ferrous bis-glycinate has been successfully used for fortification of whole cow's milk and maize and wheat flours [36]. Field studies, using milk fortified with 3 mg of ferrous bis-glycinate without addition of ascorbate, have shown that up to 40 % of the amino acid chelate is absorbed [37,38]. Studies using water solutions of 55Fe-labelled bis-glycine chelate proved better absorption than ferrous ascorbate, and that its absorption is regulated by the iron stores of the body [35]. In addition, its low pro-oxidant or rancidity properties are advantageous when used as a fortificant in fluid, high fat vehicles. Ferrous bis-glycinate is stable in the ferrous form when exposed to ambient air and temperature between pH 3 and 10. When stored in tetra-pack containers, it has a shelf life of over six months at room temperature.

More recently, a new tasteless chelate, in which iron is chelated with three molecules of glycine (ferric tris-glycinate), has been used successfully to fortify sugar for industrial use in Brazil [37]. This tris-glycine chelate causes no organoleptic changes.

Bovell-Benjamin et al. [39] compared the absorption of iron from ferrous sulphate, ferrous bis-glycinate and ferric tris-glycinate added to a whole-maize meal and concluded that better iron absorption was obtained from ferrous bis-glycinate than from ferric tris-glycinate or ferrous sulphate. It was also concluded that ferrous bis-glycinate was an effective and safe source of iron, particularly useful as an iron fortificant in phytate-rich diets.

At present, whole fluid milk and other dairy products, fortified with iron bis-glycine, are available in many countries of Latin America and Europe. Although more expensive by weight, this advanced fortificant can be used more sparingly and can thus be more cost-effective in delivering essential micronutrients to the consumer.

FOOD VEHICLES USED FOR IRON FORTIFICATION IN SOUTH AFRICA (SA)

One of the major problems frequently encountered in iron fortification is the choice of the form of iron to be added. There are only a few successful applications of iron fortification in South Africa. Table 2 is the latest results of an investigation on food products with added iron available in SA. Cereal products are the most widely used vehicles for iron fortification. Since reduced iron is inert organoleptically, it is used to fortify ready-to-eat breakfast cereals and maize meal, though it has a relatively low absorption. Desiccated freely soluble ferrous sulphate is the best absorbed, but is also the most chemically reactive, producing off flavours and colour and is used to fortify low acid foods and infant formulae and cereals. Ferric pyrophosphate interacts least with food components, and its bioavailability is considered to be good. In the acid environment of the stomach, its solubility and, thus, bioavailability is increased. The compound can be dispersed and suspended in a liquid food. In SA it is used to fortify a malted drink. Ferrous fumarate is better absorbed and found to be suitable for fortification of cereal-based weaning foods.

Like other developing countries, food fortification is an essential element in nutrition strategies to alleviate micronutrient deficiencies in SA. It is a dynamic area developing in response to the needs of population groups and industry. In SA, the Directorate of Nutrition within the Department of Health (DOH) spearheaded mandatory food fortification by establishing a food fortification task group (FFTG). The FFTG, comprising of representatives from DOH, industry, consumer organisations, professional associations and international organisations was established to assist the DOH with a food fortification programme for SA. The FFTG developed a framework with all the activities to be conducted, for example, situation analyses, feasibility studies and plan development. Efforts should continue to develop improved and new systems of delivering micronutrients to target populations through appropriate fortification procedures.

CONCLUSION

Iron deficiency, one of the most prevalent problems of micronutrient malnutrition, occurs in many developing countries. The impact of iron deficiency and IDA on the individual can result in lifelong disadvantages. Causes of the problem are many, but the principal cause is lack of iron-rich food in the diet. One of the best strategies to eliminate or markedly reduce iron malnutrition is through food fortification, with the goal of increasing the level of iron consumption to improve nutritional status. Several options exist with respect to iron fortificant and food vehicle selection. Various factors must be considered before initiating a fortification programme. These include cost effectiveness of fortification in increasing absorbable iron, palatability of the fortified food and the etiology of iron deficiency. As most iron-fortified foods contain potential absorption inhibitors, it is essential to protect the fortification iron to ensure adequate absorption.

In recent years, food fortification has become a more realistic and accessible option for SA to end micronutrient malnutrition. Like in other developing countries, iron fortification is the optimal approach to reducing the prevalence of ID in SA. To improve the effectiveness of the micronutrient interventions, a number of foods have successfully been fortified with different iron fortification compounds. The iron-fortified products in SA include ready-to-eat foods, such as baby formulae, weaning foods, breakfast cereals, and some nourishing powdered drinks. The iron fortificants used in SA include reduced iron, dried ferrous sulphate, ferrous fumarate and ferric pyrophosphate. All these fortificants have a relatively good bioavailability of iron. However, prevalence rates of ID continue to be high in SA. It is, therefore, necessary to increase efforts in developing improved iron fortification interventions, research and produce more iron fortified staple foods and to select more appropriate iron fortificants for different foods in a combined strategy to prevent and control iron deficiency.

When establishing strategies for anaemia prevention, it is important to realise that micronutrients, other than iron, are important in anaemia prevention. In addition to iron, copper, vitamins A, B2, B12, C, and folate are essential for Hb formation and it is thus essential to consider the total diet and not concentrate in iron alone when addressing anaemia prevention. The premise of any fortification program should be to design a diet to increase the availability of nutrients needed to maintain good iron status.