of home-prepared
soy-corn milk ± a
protein beverage
Olusola Omueti
E.B. Oguntona
Olayinka Jaiyeola and
O.A. Ashaye
Soyabean (Glycine maxL) has recently attracted greater attention in Nigeria as an important crop that can be used to increase protein intake and combat protein/calorie malnutrition in the country (Rootet al., 1987). Meaningful achievements have been made in the area of promotion of soyabean as a nutritional supplement used to revive malnourished children in various places in Nigeria, e.g. the Kersey children's home in Ogbomosho and Oni Memorial Children's Hospital (Weingartner, 1987). In these locations, malnourished infants who are unable to consume solids are placed on a diet of soy-milk which is followed by traditional foods supplemented with soybean fractions.
By virtue of its high protein content and generous amount of essential amino acids, especially lysine, tryptophan and threonine, soybean has been identified as a premier crop in finding solutions to problems of malnutrition in Nigeria if the nutritive potentials of the crop are utilized. Soybean is deficient in sulphur amino-acids, especially methionine but rich in lysine. On the other hand, cereals are rich in sulphur amino acids, e.g. methionine, but deficient in lysine and tryptophan (Mitchell and Smuts, 1932). Therefore, in a blend of soybean and cereal, the lysine from soybean complements its deficiency in cereal while methionine acts vice versa in soybean (Bressani, 1981). Thus, the nutritional value of soybean products can be enhanced if supplemented with cereals (Bressani, 1981; Serna-Saldivaret al., 1991).
The fresh form of maize usually called the green maize is widely eaten in various forms in Nigeria (Eijinattem, 1965; Osanyintolaet al., 1992). When in season, the cobs of green field maize litter the environment because of lack of storage and diversified utilization technology. The grain of the green field maize, when tender, contains milky juice. Over the past decade, soy-milk processing and usage had received unprecedented acceptability in Nigeria. Thus, a technology that can incorporate The authors
Olusola Omueti(drart@infoweb.abs.net) is Biochemical and Nutritional Evaluator of Food and Crops, at the Institute of Agricultural Research & Training, Obafemi Awolowo University, Ibadan, Nigeria.
E.B. Oguntonais Animal Nutrition Researcher, at the Department of Animal Nutrition, University of Agriculture, Abeokuta, Nigeria.
Olayinka JaiyeolaandO.A. Ashayeare Food Technology Researchers, both at the Institute of Agricultural Research & Training, Obafemi Awolowo University, Ibadan, Nigeria.
Keywords
Weaning, Soya, Nutrition, Corn
Abstract
Freshly-blanched soybean seeds, mixed with grains of freshly-harvested green field maize were combined, in ratios of 5:1 (A), 4:1 (B), 3:1 (C); 2:1 (D), 1:0 (E) and 0:1 (F), to prepare soy-corn milk. Dried flakes of soy-corn milk were analysed for theirin vitro digestibility (IVD) and assessed on the performance of rats fed with the test materials. Protein content of the blends increased with the increased amount of soybean in the blend. The IVD of Blend C (88 per cent) was superior to the IVD of all other test blends but was similar to that of casein (90 per cent). Highest weight gain, feed intake, estimated nitrogen intake, PER, BV and NPU were associated with Blend C, and values reported for this blend compared favourably with a casein diet. Implications of the results are discussed in terms of searching for a means of combating malnutrition.
Electronic access
The current issue and full text archive of this journal is available at
http://www.emerald-library.com The authors express their gratitude for the financial sponsorship of this project by the Regional Research Project on Maize and Cassava (RRPMC) through the International Institute of Tropical Agriculture, Ibadan, Nigeria.
Nutrition & Food Science
the tender and juicy grain of green field maize into soy-milk processing to boost its nutritional value is a useful innovation. Therefore, the complementary utilization of fresh green maize and freshly-blanched soybean seeds was developed to produce an acceptable beverage named soy-milk (Omueti and Ashaye, 1994). Because of the acceptance of this cereal by both adults and children, it is a highly-favoured option for use as a weaning liquid food, and as a nutritious food for malnourished children. There is, therefore, the need to evaluate the nutritional value of this beverage. The objectives of this study were to determine thein vitrodigestibility (IVD) of the beverage, evaluate the performance of weanling rats fed with the beverage, and relate the results from one objective to the other.
Materials and methods
Preparation of soy-corn milk
Soy-corn milk preparation has been described elsewhere (Omueti and Ashaye, 1994), but only briefly. Fresh cobs of green field maize (white variety) at the tender and milky stage were purchased from the early-morning market. The tender grains were carefully removed from the cob and kept in a polythene bag. Seeds of soybeans (variety TGX-923-2E) were obtained from the Institute of Agricultural Research and Training seed store. The seeds, previously soaked overnight, in a 1:5 ratio of seeds to water were blanched (25min). Drained seeds were combined with the maize grain in a soybean-to-maize ratio of:
The treatment of each 300g portion was milled in a locally-made attrition mill. The slurry was thoroughly mixed with 1.5l of water and sieved with fine-mesh nylon cloth. The filtrate was brought to its boiling point and allowed to boil for 8-10min, cooled and dried in batches at 508C in stainless steel trays in a gallenkamp draft oven. The dried form was recovered as flakes. Batches of each treatment were combined for the IVD and rat feeding experiment.
IVD
IVD was determined using the multi-enzyme method described by Hsuet al.(1977) as modified by Satterleeet al.(1979). Soy-corn flakes were ground to pass through an 80-mesh screen and used for the determination. All enzymes were purchased from Sigma chemical company, USA. Casein was used as a control.
Rat studies
Constituents of test samples are given in Table I. Diets were formulated as given in Table II.
Weanling Wistar rats, obtained from the Zoology Department, University of Lagos were used. They were bred at the University of Agriculture, Abeokuta and the National
Table IIFormulated diet
Ingredient Percentage
Cassava floura 54
Total 100
Standard diet
Milk powder 7
Dried meat powder 6
Dried fish powder 2
Vegetable oil 15
Sucrose 15
Dried mixed vegetables 8
Cassava flour 10
White flour 36
Sodium chloride 1
Total 100
Note:aTest material (and casein, in the case of
reference diet) were substituted at the expense of cassava flour
Institute for Medical Research, Yaba. Housing was in galvanised, wire-top cages in a temperature controlled room. Experimental animals were selected from 200 male weanling rats of similar weight.
Experiment design
A total of 140 weanling rats were used for every trial. Each diet (Table III) was allocated 20 individually-caged rats. The experimental procedure adopted was
essentially as described by Campbell (1963). For biological value, the formula of Bender and Miller (1953) was used. In the
determination of net protein utilization (NPU), a version of the procedure described by Miller (1963) was adopted, but modified in two ways:
(1) the weaning diet was fed from 23 to 33 days; and
(2) the assay was for seven days, i.e. 33-40 days old, so that the factor for N:H20 ratio applies.
Chemical analysis
Moisture content determination was carried out according to AOAC procedure for all samples. Nitrogen was determined by the AOAC (1984) method, as described in the ODA/NRI laboratory manual in the analyses of the soy-corn milk flakes.
Results and discussion
Protein content
The protein contents of the test samples are provided in Table I. Addition of soybean to the maize increased protein content as the proportion of soybean was increased in the mixture. Similar observations had been reported earlier (Bressani et al., 1979). The
maize-milk flakes alone are, as expected, very low in protein (2.49 per cent) compared to the soybean/corn milk flakes which contained up to 24.9 per cent. Much of the crude protein in maize milk alone would have been left in the residue.
IVD
The IVD of the various soy-corn milk samples is represented in Figure 1. The protein digestibility of Blend C compared favourably with that of casein and its value (88.0 per cent) is significantly superior (p< 0.05) to that of soy-milk alone (82.1 per cent). Although Blend C contained lower protein content (see Table IV) than Blends A, B and E, the superior IVD is a reflection of more balanced essential amino acids in Blend C than in the other blends. This is a key factor in the determination of protein quality (Flodin, 1953; 1956). The results also indicate that the blending of maize with soybean significantly improved the nutritional quality of the soy-corn milk compared to that of the soy-milk alone. These results confirm the expected beneficial complementarity of amino acids from cereal and legume. Therefore, the deficiency of lysine in sole maize and methionine in sole soybean are being offset in their mixture (Bressaniet al., 1979).
Table IIIExperimental rat diets based on soy-corn milk flakes
Diet
A B C D E F Soya-to-corn ratio 5:1 4:1 3:1 2:1 1:0 0:1
Starch 210 210 210 210 210 210
Sucrose 120 120 120 120 120 120
Vegetable oil 80 80 80 80 80 80
Premix 50 50 50 50 50 50
Cassava 422 419 410 392 437 ±
Soy-corn milk flakes 118 121 130 148 103 666
Total 1,000 1,000 1,000 1,000 1,000 1,000
Crude protein (per cent) 24.9 24.1 22.5 20.4 29.9 1.5
Figure 1IVD of soy-corn milk flakes
Table IVCrude protein content of soy-corn milk flakes
Sample identification
Soybean-to-maize ratio
Crude protein (per cent)
A 5:1 24.90
B 4:1 24.10
C 3:1 22.50
D 2:1 20.40
E 1:0 29.91
Rat feeding studies
Table V gives the performance of rats fed with the formulated diets as well as a casein diet. Food intake was high with diets A, B and C (395g, 418g and 421g, respectively) suggesting diet palatability attributed to the mixture of maize and soybean. There was concomitant high nitrogen intake and high weight gain. The present results showed that between 16 and 25 per cent of maize addition to sole soy-milk resulted in the improvement of the nutritional quality of soy-corn milk. It appears that the diets of soy-corn milk in various soybean-to-maize ratios similarly affected weight gain as the PER and the low feed intake of the rat fed on the maize-milk-alone diet suggests poor palatability.
Overall assessment of Blend C indicates that this blend compared favourably with casein in terms of biological value (BV), net protein utilization (NPU), protein efficiency ratio (PER) and IVD. The results presented here show that the combination of fresh green field maize with soybean to produce soy-corn milk had a parallel and positive effect on the BV and NPU. Similar results have long been reported when whey protein concentrate was added to maize diet in rat feeding studies (Kilonzo, 1978).
As expected, a diet based on maize milk alone (Blend F) was inferior to all other test samples in terms of all the parameters measured. This could be attributed to the low protein content as well as the inadequate lysine content of Blend F, with lysine becoming a limiting amino acid.
The results of the IVD corroborate those of rat feeding studies regarding the superiority of protein quality of Blend C over the other test blends. Thus, the development of soy-corn
milk is a positive step towards improvement in human nutrition where protein-calorie malnutrition is rampant. Since this product has been found to be acceptable (Omueti and Ashaye, 1994), soy-corn milk is a possible option for combating malnutrition in developing countries.
References
AOAC (1984),Official Methods of Analysis, 14th ed., Association of Official Analytical Chemists, Washington, DC.
Bender, A.E. and Miller, D. (1953), ``A neco-brief method of estimating net protein value'',Biochem. Journal, Vol. 53 No. 7 (Abstract).
Bressani, R. (1981), ``The role of soybeans in food system'',Journal of American Oil Chemists' Society, Vol. 58, pp. 392-400.
Bressani, R., Braham, J.E., Elias, L.G. and Rubio, M. (1979), ``Further studies on the enrichment of lime-treated corn with whole soybeans'',Journal of Food Science, Vol. 44, pp. 1707-10.
Campbell, J.A. (1963), ``Method for determination of PER and NPR'',Evaluation of Protein Quality, Publication 1100, NAS-NCR, Washington, DC.
Eijinattem, O.L.M. (1965),Towards the Improvement of Maize in Nigeria, Veenan and Zones, Wageningen. Flodin, N.W. (1953), ``Amino acids and proteins. Their
place in human nutrition places'',Agri. Food Chem, Vol. 1, pp. 222-35.
Flodin, N.W. (1956), ``The philosophy of amino acid fortification of foods'',Cereal Sci. Today, Vol. 1, p. 165.
Hsu, H.W., Vavak, D.L., Satterlee, L.D. and Miller, G.A. (1977), ``A multi-enzyme technique for estimating protein digestibility'',Journal of Food Science, Vol. 42, pp. 1269-73.
Kilonzo, J.M. (1978), ``The improvement of the biological value of food plants from Kenya by combinations with vegetable proteins, animal proteins and limiting amino acid'',Nutr. Rept. Inter., Vol. 18, pp. 599-609.
Miller, D.S. (1963),New Procedure for NPU Determination. Laboratory Handbook, Queen Elizabeth College, University of London.
Mitchell, H.H. and Smuts, D.B. (1932), ``The amino acid deficiencies of beef, wheat, corn, oats and soybeans for growth in white rats'',J. Biol. Chem., Vol. 95, pp. 263-81.
ODA/NRI (Overseas Development Administration/Natural Resources Institute) (1994),Analytical Laboratory Procedures, NRI, Chatham.
Omueti, O. and Ashaye, O.A. (1994), ``Home-level preparation, nutrients content and acceptability of soy-corn'', in Chainnuvati, C. and Sarobol, N.N. (Eds),Proceedings of the World Soybean Research Conference V, pp. 579-83 (Supplement).
Osanyintola, O.J., Mareck, J.H. and Akingbala, J.O. (1992), ``Effect of time of harvest and variety on the quality of boiled green field maize (Zea mays Linn.), Tropical Science, Vol. 32, pp. 369-76.
Table VPerformance of rats on test diets
Diets
Root, W.R., Oyekan, P.O. and Dashiell, K.E. (1987), ``West and Central Africa: Nigeria sets example for expansion of soybeans'', in Singh, S.R., Rachie, K.O. and Dashiell, K.E. (Eds),Soybean for the Tropics, Research and Utilization, pp. 81-91.
Satterlee, L.D., Marshall, H.F. and Tennyson, J.M. (1979), ``Measuring protein quality'',J. Am. Oil Chem. Soc., Vol. 56, pp. 103-9.
Serna-Saldivar, S.O., McDonough, C.M. and Rooney, L.W. (1991), ``Millets'', in Lorenz, K. and Kulp, K. (Eds), Handbook of Cereal Science and Technology, Chapter 6, Marcel Dekker, New York, NY. Weingartner, K.E. (1987), ``Processing, nutrition and
