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Nutritional evaluation of gado-gado a traditional Sudanese food OMAR M. SALIH, RAKHA B. BABIKER and ABDEL AZIM A.M. NOUR^1
Food Research Centre, P.O. Box 213 Khartoum North, Sudan (Received 8 December 1994; accepted 17 November 1995)
Code Number: CS96046
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No associated graphics filesABSTRACT The proximate chemical composition and micro-biological quality of gado-gado a traditional Sudanese food made from pearl millet (Pennisetum darfuricum) were studied. Comparison with grains showed that the chemical composition was affected during the preparation of gado-gado. An increase in starch content (43%), and a decrease in fibre (47%), ash content (50%) and fat content (17%) resulted from dehulling the grains. Though there was a 16% decrease in protein content, gado-gado was rich in essential branched chain amino acids. Amino acid concentration was comparable to that of the FAO's reference protein. The microbiological results obtained indicated that, with the exception of the coliform count, the parameters tested were within acceptable ranges. Key Words: Chemical composition, nutritional quality, Pennisetum darfuricum, safety, the traditionally processed food, Western Sudan RESUME La composition chimique et la qualite microbiologique de Gado-gado, un aliment traditionnel soudanais a base de millet (Pennisetum darfuricum), etaient etudiees. La comparaison de grains a montre que la composition chimique etait modifiee durant la preparation de gado-gado. L'augmentation en teneur d'amidon (43%), la reduction de fibres (47%), la teneur en cendres (50%) el la reduction en teneur de graisse (17%) provenaient du nettoyage de grains. Bien qu'il y avait une reduction de 16 % en teneur de proteine, le gado-gado etait riche en chaines d'amino acides essentiels. La concentration d'amino acides etait plus elevee que celle indiquee par FAO. Les resultats microbiologiques obtenus indiquaient qu' a l'exception du comptage de coliformes, les autres parametres testes etaient dans la gamme acceptable. Mots Cles: Composition chimique, qualite nutritionnelle, Pennisetum darfuricum, innocuite, aliment traditionnellement prepare, Sudan de l'ouest INTRODUCTION Pearl millet or dukhn (Pennisetum darfuricum) is the main staple food in Western Sudan. It is mainly found in the Meidob hills, in a clay valley below Jebel Kaboija (Andrews, 1956) and is intensively consumed in the Darfur region. The grains of dukhn have been described by Fox and Norwood (1982) as caryopses (grain) and usually light to dark grey in colour. The grains are very similar to Pennisetum americanum which is cultivated in Angola and Namibia. FAO/WHO (1988) reported that dukhn contains 9-16% protein which, like all cereal proteins, is low in lysine. The seed compared with rice and wheat contains a rich source of carbohydrates and B vitamins. Gado-gado is a food prepared from dukhn flour and is considered as the most important food provision for nomads in Western Sudan. They benefitted from stored sticks of gado-gado during the 1984 famine (Salih, 1991). Due to the importance of gado-gado as a traditionally processed food, this paper highlights its quality using chemical and microbiological methods. MATERIALS AND METHODS Preparation of gado-gado. Dukhn grains were decorticated using a funduk (a traditional wooden mortar and pestle). The seeds were dehulled and the grains washed and sun-dried. The grains were then ground using a Murkhaka (a traditional mill consisting of two broad stones). A dough was prepared and made into small balls which were placed on a hot plate with hot water and left for 30 minutes until they turned yellow. The water was discarded and the balls remixed to form a dough which was returned to the funduk and rebeaten with the addition of water. The beating continued until the dough became hard and small balls 3-5 cm in diameter were formed. Flour was added to cover the balls to produce gado-gado, which was ready for consumption. They can be served with sour milk or sun-dried for future need. Proximate and elemental analysis. The proximate analyses were conducted using standard methods (Anon., 1982). Samples were digested with a nitric/perchloric acid mixture. Potassium, sodium, calcium, magnesium, phosphorus, sulphur, iron, zinc, manganese and copper were determined using an inductively coupled plasma optical emission spectrometer, Perkin Elmer Plasma II model.
Amino acid analysis. Milled gado-gado samples (500 mg) were refluxed, using the open flask method of Mondino and Bongiovanni (1970), in a 500 ml conical flask with constant boiling in HCl (400 ml) for 22 hr. The hydrolysate was cooled rapidly, 4 mM norleucine (20 ml) added as an internal standard, and the solution diluted to a final volume of 500 ml with deionised distilled water. After filtration, an aliquot (25 ml) was evaporated to dryness at 60 C under reduced pressure. Residual HCl was removed by twice dissolving the residue in distilled water and evaporating to dryness. The washed residue was then redissolved in 0.2 M lithium citrate buffer pH 2.2 to give a suitable concentration for chromatographic separation of the individual amino acids. Chromatography was carried out on an LKB Model 4400 amino acid analyser using a column (270 x 4.6 mm) packed with polystyrene divinylbenzene 8% cross-linked cation exchange resin (8 um mesh size) and a 0.2-1.6 M lithium citrate buffer elution programme (Andrews, 1980). Cysteine was estimated as cysteic acid and methionine as methionine sulphone using a performic acid oxidation pretreatment before acid hydrolysis. The concentration of each amino acid was calculated using an internal standard procedure and a calibration standard being chromatographed between every five samples. Peak areas were measured using a Trivector Computing Integrator. The results were expressed as grams of amino acid per 16 g of total nitrogen. Sugar content. The homogenised sample (500 mg) was extracted by incubating with water (50 ml) at 60 C for 15 min. The solution was made up to 100 ml and filtered. Sucrose, glucose and fructose were determined in the filtrate using a test kit from Boehringer (Bergmeyer and Bernt, 1974). D-glucose was determined after conversion to glucose-6-phosphate with hexokinase (EC 2.7.1.1.) by the method described below for starch determination. D-fructose was converted with hexokinase to fructose-6-phosphate which was isomerised to glucose-6-phosphate using phosphoglyceroisomerase (EC 5.3.1.90) and determined as above. The sucrose concentration was then measured by hydrolysis to glucose and fructose using invertase (EC 3.2.1.48) and redetermination of glucose. Starch determination. To the homogenised sample (500 mg) in a conical flask, was added 11 g litre^-1 HCl (50 ml). The mixture was heated for 30 min on a boiling water bath with swirling and then rapidly cooled to room temperature. The pH was adjusted to 4.5 with 5 M NaOH and the solution made up to 100 ml and filtered. Starch was determined in the filtrate by hydrolysis to D-glucose with amyglucosidase (RC 3.2.1.3) followed by the assay of D-glucose using spectrophotometric measurement of NADPH formation at 340 nm in the presence of hexokinase, glucose-6-phosphate dehydrogenase (EC 1.1.1.49), ATP and NADP using a starch test kit from Boehringer (Bergmeyer, 1984). Microbiological analysis. Thirty grams of gado gado were weighed aseptically and the sample was soaked for 15 minutes in 270 ml sterile distilled water. The sample was then homogenised for one minute in a Colworth Stomaker 400. The homogenate was used to prepare 10 fold dilutions in 9 ml aliquots sterile 0.5% (W/V) peptone water (Oxoid C37) using the method of Murray (1956). Suitable dilutions were used to determine the following: a) Total bacterial count by the pour plate method using nutrient agar (Oxoid CM3). Plates were incubated at 37 C for 48 hr. Counting was carried out by an Astell colony counter (Laboratory Service Co. Ltd., London, England). b) Coliform count using MacConkey broth (Oxoid CM5). Tubes were incubated at 37 C for 48 hr and the three tubes procedure was used for estimating the most probable number (MPN) of coliform organisms. Positive tubes were tested for the presence of E. coli (Harrigan and Mc Canoe, 1976). c) Yeast and mould count using Malt Extract Agar (Oxoid CM59). Plates were incubated at 25 C for 72 hr. d) Total staphylococcal count using Mannitol Salt Agar (CM85) incubated at 37 C for 72 hr. e) Detection of salmonella was conducted as described by Harrigan and Mc Cance (1976). Isolation and identification of micro-organisms. Ten colonies were-picked from the nutrient agar plates and purified by inoculation of discrete colonies onto nutrient broth (Oxoid CMI) and incubated at 37 C for 24 hr. A loopful was streaked into nutrient agar plates and incubated at 37 C for 24 hr. The purified colonies were then subjected to identification according to the method described by Cowan and Steel (1974). RESULTS AND DISCUSSION Proximate chemical composition. Values for proximate composition are presented in Table 1. The method of preparation of gado-gado seems to have a great effect on the chemical composition. Dehulling of the grains affected the final composition of the product, as there was a great increase in starch content and a decrease in crude fibre and ash contents. Results obtained also showed a decrease of 17% in fat content compared to dukhn Pennisetum darfuricum grains (Salih et al., 1992). Protein quality. The amino acid composition of dukhn from this study is similar to that reported by FAO (1976). Table I shows that the crude protein content of dukhn is 15.9%. This value is somewhat higher than that of the local Sudanese varieties of sorghum (Purseglove, 1972). Protein content of gado-gado decreased by 16% from that of parent dukhn but is still comparable to the protein content of the sorghum grains. TABLE 1. Chemical composition (g kg^-1 DM) of gado-gado, a processed food made from pearl-millet dukhn (Pennisetum daryfuricum) in Sudan compared to dukhn grains
Soluble carbohydrates Other
--------------------------- carbo-
Ash Crude Oil Crude Starch Sucrose D- D- hydr-
protein glucose fructose ates
--------------------------------------------------------------
Gado-gado
1.3 13.4 1.1 1.1 80.7 0 1.3 0.4 0.7
Dukhn
2.6 15.9 5.9 2.1 56.5 0.8 1.2 0.8 14.2
--------------------------------------------------------------
Results presented in Table 2 show that gadogado is rich in essential branched chain amino acids, valine, leucine and isoleucine and the aromatic amino acids are in excess of that of the FAO reference protein (FAO, 1976). Sulphur amino acids remain in nutritionally adequate concentration in gado-gado, after processing, and quantities found are more than those of the FAO reference protein (FAO, 1976). Available carbohydrates. The level of soluble carbohydrates is slightly lower in gado-gado compared to dukhn which can be attributed to the method of processing. Mineral content. The mineral content of gadogado is shown in Table 3. The concentration of minerals is similar to that of dukhn except for P, K and Mn which indicated that overall, processing did not affect the mineral content. Of the trace elements, iron concentration in gado-gado is at the lower end of the range found in plant foods, 10-230 mg kg^-1 (Kabata-Pendias and Pendias, 1984). Microbiological quality. The total bacterial count and the mould count (Table 4) were found to be in the recommended range (Dirar, 1974). He recommended 1 x 10^5, 1 x 10^4 and 15 cells g^-1 for total bacterial, mould and coliform counts, respectively, as microbial standards for dehydrated food in all African and Arab countries. Identification of the bacterial isolates showed that the spore forming organisms comprised more than 85% of the total bacteria. This finding agreed with those of Sheneman (1973). The coliform number was high < 1100/g and this could be attributed to the unsatisfactory sanitary conditions practiced and the lack of preventive measures to reduce the chance of dusting the finished product. No staphylococci, salmonella or E. coli were detected. CONCLUSION The complicated method of processing gado-gado affected its nutritive values as it was found to be higher in starch content than dukhn. Though there was some decrease in its protein content, it was found to be rich in essential branched chain aromatic and sulphur amino acids. The microbiological results obtained indicated that all parametres tested were within an acceptable range except for the coliform count. TABLE 2. Comparison of amino acid composition of proteins of gado-gado with those of durkhn grains (Pennisetum daduricum)
Amino acid concentration [ g (16 g N)^1]
--------------------------------------------------------------------
Aspartic Threo- Serine Gluta- Proline Glycine Alanine Valine Cystine
nine mic
acid
------------------------------------------------------------------------------
Gado-gado 6.3 2.7 3.6 19.0 6.4 1.8 6.6 4.6 0.8
Dukhn 10.2 4.5 4.5 25.6 10.2 3.6 9.4 6.9 2.0
FAO
reference
protein 4.0 5.0 3.5
Table 2 contd./
Amino acid concentration [ g (16 g N)^1]
------------------------------------------------------------
Meth- Iso- Leucine Tyrosine Phenyl Lysine Histi- Arginine
ionine leucine -alanine dine
----------------------------------------------------------------------------
Gado-gado 1.5 3.8 8.4 2.8 4.5 1.4 1.6 2.7
Dukhn 2.6 5.0 12.5 3.8 6.0 3.5 2.5 4.8
FAO
reference
protein 3.5 4.0 7.0 6.0 5.5TABLE 3. Elemental composition of Gado-gado compared to that of dukhn
9 kg^-1 DM mg kg^-1 DM
---------------------------------- -----------------
S P MG Ca Na K Zn Fe Mn Cu
----------------------------------------------------------
Gado-gado
0.14 0.18 0.09 0.05 0.02 0.23 33 58 9 6
Dukhn
0.16 0.26 0.14 0.03 0.01 0.42 41 66 18 8
TABLE 4. Microbiological status of Gado-gado
---------------------------------------------------
Total bacterial count Log[10] 5.1
Yeast and mould Log[10] 4.1
Coliforms < 1100/g
Salmonella Nil
Staphylococci Nil
E. coli NilACKNOWLEDGEMENTS We are grateful to Mr. D. Annette for his skilled assistance with amino acid analysis. REFERENCES Andrews, F.W. 1956. Flowering Plants of Anglo-Egyptians Sudan. Vol. 1-3. T. Buncle and Co., Arbroath, Scotland. Andrews, R.P. 1980. Analysis of human serum and plasma using the LKB 4400 amino acid analyser. Technical leaflet PCN 12. LKB Instruments Ltd., Croydon, Surrey, U.K. Anonymous, 1982. Statutory Rules of Northern Ireland. No. 338 Agriculture. The Feeding Stuffs (sampling and analysis) Regulations (Northern Ireland) 1982 - HMSO, Belfast. Bergmeyer, H.U. (Ed.). 1984. Methods of Enzymatic Analysis. 3rd edn. Vol. 4. Verlag Chemie, Deerfield Beach, Fla. Bergmeyer, M.U. and Bernt, E. 1974. In:Methods of Enzymatic Analysis. 2nd edn, Vol. 3. Bergmeyer, M.U. (Ed.), pp. 1176-1179. Verlag Chemie, Weinheim/Academic Press, New York. Cowan, S.T. and Steel, K.J. 1974. Mannual for the Identification of Medical Bacteria. 2nd Ed., London, Cambridge, University Press. Dirar, H.A. 1974. Microbial spoilage of foods: A Review. Sudan Journal of Food Science and Technology 6:61-65. FAO, 1976. Amino-Acid Content of Foods and Biological data on Proteins. Nutrition Division, FAO, Rome. FAO/WHO, 1988. Traditional Food Plants. FAO Food and Nutrition paper 42. FAO, Rome. Fox, F.W. and Norwood, M.E. 1982. Food From the Veld; Edible Wild Plants of Southern Africa. South African Institute for Medical Research. Delta Books (Pty) Ltd., Johannesburg and Cape Town. Harrigan, W.F. and Mc Cance. M.E. 1976. Laboratory Methods in Food and Dairy Microbiology. Academic Press, New York. 452pp. Kabata-Pendias, A. and Pendias, H. 1984. Trace Elements in Soils and Plants. CRC Press Inc., Boca Raton, Florida. Mondino, A. and Bongiovanni, G. 1970. An experimental study of amino acid degradation under open flask hydrolysis conditions. Journal of Chromatography 52:405-413. Murray, J.G. 1956. A technique for making dilutions. Journal of Applied Bacteriology 19:212. Purseglove, J.W. 1972. Tropical Crops, Monocotyledons l-2.Longmans, London. 607pp. Salih, O.M. 1991. Biochemical and Nutritional Evaluation of Famine Foods of the Sudan. Ph.D. Thesis, University of Khartoum. 100pp. Salih, O.M., Nour, A.M. and Harper, D.B. 1992. Nutritional quality of uncultivated cereal grains utilized as famine foods in western Sudan as measured by chemical analysis. Journal of Science and Food Agriculture 58: 417-424.
Sheneman, J.M. 1973. Survey of serobic mesophilic bacteria in dehydrated onion products. Journal of Food Science 38:206. Copyright 1996 The African Crop Science Society
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