African Journal of Food, Agriculture, Nutrition and Development Rural Outreach Program ISSN: 1684-5358 EISSN: 1684-5374 Vol. 4, Num. 1, 2004

African Journal of Food Agriculture Nutrition and Development, Vol. 4, No. 1, 2004

IRON BIOAVAILABILITY IN CAMEROON WEANING FOODS AND THE INFLUENCE OF THE DIET COMPOSITION

La biodisponibilité du fer dans les aliments de sevrage camerounais et l'influence de la composition diététique

Kana Sop MM*¹, Zollo PHA¹ and F Ndifor¹

*Corresponding author Email: kanamod@yahoo.com
1Department of Biochemistry, University of Douala, Fac. Sces, P.O. Box 24157, Douala, Cameroon

Code Number: nd04006

ABSTRACT

The objective of the study was to assess the "in vitro" bioavailability of iron in the main Cameroon traditional complementary foods identified during interviews of one month with 91 mothers of weaning babies of up to 30 months, in order to identify and select good food sources of iron to fight against iron deficiency and iron deficiency anaemia in pre-school children.
The foods were selected for their frequent consumption, cooked in triplicate as described by mothers, freeze dried and kept at - 20 °C or analysed chemically.
The dry weight (DW) was obtained by drying the fresh cooked food in the drying oven at 105 °C during 48 hours. Total levels of iron were assessed by Flame Atomic Absorption Spectrometry. Non hem iron levels were determined with Bathophenanthroline colorimetric method. The "in vitro" dialyzable iron values were determined by the extrinsic radio labelled tag method using ⁵⁹Fe.
Total iron levels generally ranged from 4.68 ± 0.5 (in fermented maize gruel) to 51.51 ± 3.73 mg/100 gDW (in maize meal with a vegetable, Corchorus olitorius sauce). Non hem iron values were higher than hem iron values calculated from the difference between total and non hem iron. They ranged from 3.11 ± 0.09 (in sweet potato with pear) to 47.64 ± 4.68 mg/100 g DW (in maize meal with Corchorus olitorius sauce). Dialyzable iron values expressed as a percentage (%) of non hem iron which ranged between 0.89 ± 0.13 (in maize meal with, Corchorus olitorius sauce) and 18. 68 ± 2. 11% (in mashed Irish potato with fish). Dialyzable iron value were enhanced with lime juice and significantly reduced by legumes (beans, soy bean, and groundnut), egg and egg yolk.
Irish potatoes based diets were the best sources of dialyzable iron. Iron intakes were sufficient for most balanced diets to cover the recommended daily intakes of iron for children seven months of age.

Key words: Weaning, foods, iron, bioavailability, nutrients

Resume

La présente étude porte sur l'évaluation de la biodisponibilité du fer "in vitro" dans les principaux aliments de complément camerounais identifiés lors des enquêtes menées auprès des femmes ayant des enfants en âge de sevrage (jusqu'à 30 mois). Le but était de sélectionner et vulgariser les aliments riches en fer afin de lutter contre la déficience en fer et l'anémie ferriprive chez les enfants d'âge préscolaire.
Les aliments ont été sélectionnés selon la fréquence de leur consommation, préparés en triple échantillonnage suivant la méthode décrite par les mères, séchés à froid et gardés à une température de -20 °C ou soumis à l'analyse chimique. La matière sèche (MS) a été obtenue en séchant les aliments cuits frais au four à 105 °C pendant 48 heures. Les teneurs en fer totales ont été déterminées par spectrométrie d'absorption atomique dans la flamme, les taux de fer non héminiques avec la méthode colorimétrique à la Bathophénanthroline et les taux de fer dialysable « in vitro » avec la méthode d'étiquetage par radio-marquage extrinsèque au ⁵⁹Fe.
D'une manière générale, les teneurs en fer totales vont de 4,68 ± 0,5 (dans la bouillie de maïs fermenté) à 51,51 ± 3,73 mg/100MS (dans la farine de maïs avec légume, sauce au Corchorus olitorius ). Les taux de fer non héminiques sont plus élevés que les taux de fer héminiques calculés à partir de la différence entre le fer total et le fer non héminique. Ils vont de 3,11 ± 0,09 (dans les patates douces avec poire) à 47,64 mg/100 g MS (dans la farine de maïs avec sauce au Corchorus olitorius ). Les taux de fer dialysable exprimés en pourcentage (%) du fer non héminique vont de 0,89 ± 0,13 (dans la farine de maïs avec sauce au Corchorus olitorius ) à 18,68 ± 2,11% (dans la purée des pommes de terre avec poisson). Le taux de fer dialysable a été augmenté avec du jus de citron vert et significativement diminué avec les légumineuses (haricots, soja et arachides), les oufs et les jaunes d'oufs.
L'étude montre que les régimes alimentaires à base de pommes de terre sont les meilleures sources de fer dialysable. Les apports en fer sont suffisants dans la plupart des régimes équilibrés et couvrent la ration quotidienne en fer recommandée à partir de l'âge de sept mois.

Mots-clés : sevrage, aliments, fer, biodisponibilité, nutriments

INTRODUCTION

Iron deficiency anaemia is a serious public health problem in Cameroon. It affects young children as well as women of child-bearing age. Data from recent national surveys show that its average prevalence among children aged six to 59 months in the whole country is 38.1% [1]. According to the World Health Organization (WHO), an intervention programme to eradicate iron deficiency anemia should be carried out in any groups with the prevalence above 30% [2]. The commonest cause of this condition in infants and young children in developing countries is an inadequate supply of absorbable iron from the diet [3]. During this period of rapid growth, iron is needed for tissue generation including red blood cell production, as well as for the replacement of endogenous losses. The faster the growth rate, the more iron is needed. In this age group, care should be taken in selecting appropriate diets in order to prevent the recurrence of iron deficiency anemia. In Cameroon, traditional weaning foods are generally cereals, tuber based foods while some of the foods are of low nutrient levels with unknown chemical composition [4]. During the weaning period, only the data obtained from bioavailability studies using test meals can be used to derive simple guidelines to optimize dietary iron supply [5]. Therefore, the prevention of iron deficiency anaemia should be given a higher priority than detection and treatment. We carried out this study to assess the in vitro iron bioavailability in most commonly consumed Cameroonian weaning foods. Some enriched maize paps have also been studied as a result of a nutrition education programme. This study will enable us to identify best dietary sources of iron. Some nutrients have been assessed to evaluate their influence on the in vitro iron bioavailability.

MATERIALS AND METHODS

Materials

The test meals were selected after enquiries carried out in three Cameroonian regions: Yaoundé (Centre), Ngaoundéré (Adamaoua), Bangang and Bassessa (West) to study the weaning practices and to identify some of the foodstuffs used during weaning. Sixteen samples were chosen for their frequent consumption or by curiosity. They were cooked in triplicate and freeze-dried or dried at 80 °C and kept at -20 °C for chemical analyses. They included eight fermented enriched and non enriched maize (Zea mays) gruels, three Irish potato gruels, four maize flour meals eaten with vegetable sauces and one sweet potato with pear meal. The composition of the analyzed meals is summarised in Table 1.

Reagents

Digestive enzymes and bile salts were purchased from SIGMA. A pepsin solution was prepared by dissolving 3.2 g pepsin (cat P 7000 from porcine stomach mucosa) in 20 ml of 0.1 mol/l of HCl. The pancreatin – bile extract mixture contained 4 g pancreatin (cat P1780, from porcine pancreas) and 25 g bile extract (cat B 8631, porcine) in one litre of 0.1 mol/l NaHCO₃. All chemicals (Merck, ANALAR...) were of analytical grade. Bidistilled water was used throughout the trials. Dialysis tubing Spectra pore7 (Ø =20, 4 mm) with a molecular mass cut-off of 10 000 Da (Coleparmer instrument Co., IL, USA) was used. ⁵⁹Fe radioisotope solutions (⁵⁹FeCl₃ in 0.01 mol/l HCl) were provided by the International Atomic Energy Agency (IAEA). To minimise contamination through vessel materials, all glassware was washed with detergent, soaked overnight in 25% HNO₃, rinsed thrice with bidistilled water and dried before use. Reagent blanks were taken through the procedure and the radioactivity counted for its dialyzable iron content.

CHEMICAL ANALYSIS

Determination of “in vitro” bioavailability of iron

Gastric stage

Into 250 ml Erlenmeyer flasks (height 13.5 cm and diameter of base 8.5 cm), 10 g of sample ( in duplicate) were mixed with 80 g water. Seventy four KBq of ⁵⁹Fe were added and the pH adjusted to 2.0 by adding 6 M HCL. The total volume was brought to 100 ml. The pH was checked after 15 minutes and readjusted to 2.0. The samples were then placed for two hours at 37 °C in a shaker Waterbath with 100-120 strokes/minute and arm movement of 2 cm. The gastric digests were stored in ice for 90 minutes during which the titratable acidity was measured in an aliquot of 20 g.

Titratable acidity

Titratable acidity is defined as the amount of 0.5 M NaOH required to raise the pH to 7.5 in total volume of 25 ml. Twenty grams of homogenised gastric digest aliquot were cooled to 20 °C and 5 g of freshly prepared pancreatic mixture (enzyme) added. The pH was adjusted to 7.5 with NaOH, checked after an equilibrium period of 30 minutes and readjusted to pH 7.5 as was required and the volume noted. NaOH was used for economic reasons.

Intestinal stage

Twenty grams of homogenised pepsin digest aliquot were weighed into 250 Erlenmeyer flasks and placed in a Waterbath at 37 °C for 5 minutes. Segments of dialysis tubes (length: 250 mm from clamp to clamp) containing 25 g water with NaHCO₃ were added immediately. The volume of NaHCO₃ is equivalent to that of NaOH used to determine the titratable acidity. The weight of the dialysis bag plus the content and clips was determined. After 30 minutes, the pH was measured and 5 ml of pancreatic mixture was added to each digest. The digests were incubated in a shaker waterbath for 2 hours at 37 °C . At the end of the incubation period, the pH was measured. The Erlenmeyer flasks were weighed and closed with parafilm in order to reduce carbon dioxide losses. The dialysis bags were rinsed with bidistilled water, carefully dried and weighed. The content of each dialysis bag was transferred into gamma tubes and analysed for dialyzable ⁵⁹Fe content in the gamma counter.

The Disintegration per minute (DPM) was measured and the dialyzable iron calculated as shown below:

% of dialyzable iron: ----------- DPM/gD x WtD ---------
------------------------DPM/gRxWtR + DPM/gD x Wtd

Dry weight

Dry weight (DWt) was determined after drying the samples in the oven at 105 °C to constant weight [7].

Total proteins

Nitrogen was analysed by the Kjeldahl technique and total proteins calculated by applying the factor 6.25 to the nitrogen values [8]

Total iron, zinc and magnesium contents by Flame Atomic Absorption Spectrometry

Total iron, zinc and magnesium contents were measured by Flame Atomic Absorption Spectrometry (Spectrophotometer: ACTIUNICAM 929 serie GE 4999190) [9].

Non hem iron

Non hem iron content was estimated with the bathophenanthroline calorimetric method as described by Schriecker et al. [10]

Statistical analyses: Statistical analyses of the results were carried out according to Wilkinson [11].

RESULTS

The nutrient contents of the analysed meals are summarised in Table 2. The statistical analyses were integrated in the table in the form of letters. The values in the same column with the same superscripts are not significantly different at p < 0. 05. The values are given as mean ± Standard Deviation (SD).

Total iron levels in analysed meals were between 3.11 ± 0.09 mg/ 100 g DWt in fermented sweet potato with pear (SPP) and 51.51 ± 3.73 mg/ 100g DWt in maize meal with Corchorus olitorius sauce (CMSf), magnesium levels between 21.80 ± 0.58 mg/ 100 g DWt in F and 227.26 ± 5.14 mg mg/ 100 g DWt in SPP. The sweet potato with pear meal showed low levels of proteins and high level of magnesium.

Protein values were between 3.11 ? 0.15 g /100 g DWt in SPP and 31.16 ± 0.31g /100 g DWt in CMSk. Iron intakes estimated from the quantities of meal consumed and the iron bioavailability (25 % applied to hem iron absorption) were not sufficient to cover the daily recommended dietary allowances of infants below seven months.

Zinc levels ranged between 0.66 ± 0.05 mg/ 100 g DWt in SPP and 3.49 ± 0.4 mg/ 100 g DWt in CMSg could not meet up with the zinc daily needs of babies, regardless of the age. Non hem iron levels were between 4.16 ± 0.45 mg/ 100 g Dwt in F and 47.64 ± 4.87 mg/ 100 g DWt in CMSf. The total and non hem iron values were totally close and not statistically different in all the samples. They were lower in maize gruels, Irish potato based meals (P, PF) and maize meal without sauce (CMS). The study of the total iron and non hem iron shows that iron is more abundant in the non hem form. The addition of legumes, egg yolk and different sauces to maize meals statistically increased the total and non hem iron contents. The dialyzable iron value in SPP which is considerably rich in magnesium was slightly above those obtained in the maize gruels with egg yolk, groundnut and soy beans. The quantities of fish and beef in the tested meals were not sufficient to statistically influence the hem iron contents that were calculated by substracting the non hem iron values from the total iron values. The dialyzable iron values expressed as % of non hem iron ranged between 0.89 ± 0.13% in maize meal with Corchorus olitorius sauce (CMSf) and 18. 68 ± 2. 11% in mashed Irish potato with fish (PF) and were enhanced with the addition of lime juice and significantly reduced by legumes (beans, soy bean, and groundnut) and egg yolk (figure 1).

They were high in mashed Irish potato meals without beans, ranging from 13 ± 2.00 % to 18.68 ± 2.11%, average in maize gruels (1.32 ± 0.21% in FY to 8.11 ± 0.12% in FL) and quite low in maize flour meals and other household diets ranging from 0.89 ± 0.13% in CMSf to 2.22 ± 0.07% in CMSk. Lime juice proved to increase dialyzable iron values statistically up to 3.78 fold in gruels, whereas beans, egg yolk, soy bean, legumes, and some vegetables (Hibiscus esculentus and Hibiscus sabdariffa) tend to decrease them significantly. Red beans statistically reduced the in vitro dialyzable iron levels from 16.57 ± 1.02% in P to 0.89 ± 0.13% in PRB.

Linear correlation studies in meals with high levels of zinc and magnesium (PRB and CMSg respectively) showed a negative significant influence on the dialyzable iron values. The inhibitory effect of in vitro iron bioavailability observed with egg yolk, groundnut and soy bean was not statistically significant.

DISCUSSION

The iron contents in the analysed meals were higher in the mixture than those reported in Amaranth sauce and traditional foods eaten respectively in the Centre and Far North Provinces of Cameroon. They were slightly lower than those found by Fokou [13] when analysing the chemical composition of some vegetable based Cameroon sauces [12]. Iron levels in gruels were similar to those reported by Kombou [13] in gruels eaten in Yaoundé. The nutrient contents of foods in this study were closer to those reported in 1986 by the same author from the study of some Cameroonian household foods chemical composition [13].

Non hem values were higher than hem iron values. This means that the major part of iron in our diets is in the non hem form. Heinrich et al. [14] reported that the main form of iron in developing country meals is non hem and its bioavailability is very much influenced by the composition of the diet [14]. Dialyzable iron levels in the gruels were closer to those reported by Mbofung [15] on maize gruels eaten in Ngaoundéré [15].

The dialyzable iron levels in the meals containing meat were slightly higher than the other meals with the same composition but not containing meat. However, the difference was not statistically significant. We think that this is due to the small amount of meat in the meals which was under 1g/ 100 g of food. The inhibitory influence of zinc and magnesium on iron bioavailability was previously reported by Fairweather-Tait et al. [16].

The enhanced influence of meat and fish which are animal protein sources previously reported by Layrisse et al. [17] was positive but not statistically significant if the ratio meat /meal is 1/100 in grams. This may be due to the small amount of meat added in the analysed meals. Dialyzable iron values in the vegetable based sauces were similar to those reported by Guiro in Senegalese meals [18].

Many previous studies have shown that the inhibitory effect of dietary factors correlated with their quantities [6]. The legumes contain phytates that highly bind iron, and reduce its digestibility [5].

The protein contents of the tested meals were closer to those reported by Kombou [12], on the chemical composition of some Yaoundé household foods [13]. The zinc contents in the analysed meals were lower compared to those shown by Fokou and Teugwa on traditional meals containing vegetables, eaten in the West Province of Cameroon [12, 19]. Magnesium levels were slightly lower than those reported by Kombou on the chemical composition of household foods in Yaoundé [13]. The differences in the nutrient content observed in major cases were due to the composition of the meals studied by various authors.

CONCLUSION

From this study, we noticed that vegetable sauces which are rich in total iron are not the best sources of dialyzable iron. They should not, therefore, be specially used as weaning foods, but given occasionally to infants and children.

The enrichment of fermented maize gruels helps to ameliorate the nutrient contents, but not the in vitro iron bioavailability. We propose that, in the maize gruels enriched with soy beans, groundnut and egg yolk, as much as 20% (weight/maize paste weight) of lime juice should be added.

From the age of six months, we emphasise that weaning foods should include Irish potatoes in the regions where they are available. In the West Province of Cameroon where Irish potatoes are usually eaten with beans, this should be avoided, if care is to be taken for the iron intakes in infants and children foods.

ACKNOWLEDGEMENT

This work was partially supported by the International Atomic Energy Agency. We thank Mrs Achu Mercy for her contribution.

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