Contents - Previous - Next

This is the old United Nations University website. Visit the new site at http://unu.edu

SUPPLEMENTARY EFFECT OF BEANS FOR CEREAL GRAINS AND STARCHY FOODS

Food intake patterns in many developing countries show that beans are usually consumed with cereal grains, mainly rice and corn; in other patterns, beans are eaten with cassava or plantain. In both systems, beans play a very important role. In the first, they provide a higher protein intake and, probably more important, an amino-acid pattern that significantly increases the protein quality of the cereal-bean mixture. This is because cereal and bean proteins complement each other to a very large extent. Beans provide the lysine that is deficient in cereal grains and the latter provide part of the methionine deficient in beans. However, some limitations still persist. In starchy food (e.g., cassava) and bean combinations, the role of beans is critical in that beans only provide more total protein, but fail to increase protein quality because of a deficiency in sulfur amino acids, as previously shown.

Cereal-Bean Mixtures

Maximum protein quality values of rice and beans are shown in Fig. 5. These are obtained when 80 per cent of the total protein is derived from rice and 20 per cent from beans, either Phaseolus vulgaris or Phaseolus mungo.^10,11 The results of adding the limiting amino acids are shown on the right of the figure, demonstrating increases in quality in every case. However, addition of methionine alone to beans, although increasing quality, did not raise it to the levels in other examples, probably because of a secondary deficiency in tryptophan and low digestibility.

Additional examples of protein quality in corn and in different species of beans are shown in Fig. 6. In this case, only the main responses are shown for the soybean common corn system, beans and opaque-2 corn, and beans and common corn for purposes of showing nutritional contrasts.¹² In the first place, all three systems show maximum quality values when each component of the system provides an equal amount of protein to the total.

FIG. 4. Possible Factors Influencing the Protein Digestibility of Legumes

FIG. 5. Protein Complementation between Legumes and Rice

Second, the difference between common beans and soybeans (on the left) is due to higher content of methionine and tryptophan as well as to higher protein digestibility in soybeans in comparison with beans. Third (on the right), the difference is due to a higher lysine and tryptophan content in opaque-2 corn in contrast to common corn. Fourth (in the middle, above), the difference in quality is due to higher levels of lysine, tryptophan, and methionine in the soybean-corn, and bean and opaque-2 corn systems. Thus, any blend to the left of the maximum protein quality line (coinciding with the peak quality of the mixtures) is deficient mainly in methionine, with a secondary deficiency in tryptophan, and any blend to the right of the maximum protein quality line is deficient primarily in lysine, with a secondary tryptophan deficiency. On the basis of these results and analyses, the standards for total sulfur amino acids, tryptophan, and lysine have been calculated, as shown in Table 5. Present commonly reported levels are shown in the first column, while the middle column shows the desired values, and the last the variability reported in the literature. The values in the last column indicate the variability that exists in attaining standard or desired values.

On a more practical basis, Fig. 7 summarizes a large number of biological studies using experimental animals. However, a few of these results have been confirmed in experiments with children.^12.13 This figure is essentially the same as that shown previously, but it also provides additional information on how to increase the nutritional protein value of diets based on corn and beans. From the information shown, the following conclusions are reached, assuming protein quality in corn does not change.

TABLE 5. Nutritional Standard for Common Beans (Phaseolus vulgaris)

FIG. 6. Protein Quality of Mixtures of Corn and Beans

1. To reach level A of bean consumption, and thus protein-quality B it is necessary to increase productivity and availability of beans/ha.
2. To reach level of bean-consumption A and protein-quality C, it is necessary to increase productivity and availability of beans with higher levels of total sulfur amino acids and tryptophan. The alternative is to provide foods of good protein quality, as indicated in the figure.
3. To maintain level of bean-intake D with protein-quality E or F. it is necessary to increase levels of tryptophan in beans, with minor increases in total sulfur amino acids, keeping a high lysine content and biological availability. The alternative is to provide supplementary protein foods, as shown in the figure.
4. To maintain level of bean-intake D with a protein quality between E and B. it would be necessary to produce beans with a higher protein content and with the same amino-acid pattern. However, it would be significantly better if, together with higher protein content, beans contained higher levels of sulfur amino acids, tryptophan, and lysine.

Starchy Foods-Bean Mixtures

The nutritional significance of higher protein quantity and quality in beans is also observed in diets based on starchy food products such as plantain, cassava, or yams. A representative example is shown in Fig. 8. In this case, experimental animals were fed, ad libitum, various mixtures made from cassava flour and cooked beans, the latter with and without methionine supplementation.¹² Although not shown in the figure, protein content in the diet increases as more beans are present in the mixture. The data also show that about 32 g of beans and 68 g of cassava are needed to maintain the body weight of rats; however, only 15 g of beans and 85 g of cassava are needed for the same purpose when beans contain higher amounts of methionine. Therefore, the recommendation here would be to increase the overall quality of bean protein, as indicated previously.

OTHER ASPECTS OF INTEREST

There are other factors in beans that deserve the attention of agricultural scientists, nutritionists, and food technologists. These are factors related to acceptability characteristics and those having to do with storage and processing for consumption. Certain acceptability standards are particular to specific population groups, but one that is universal is "cookability." Beans are cooked before consumption, and the less cooking time required to make them soft, the higher their acceptability. It also appears that a bean that cooks well produces a thicker broth. Good cookability is apparently closely associated with rapid water uptake; however, the reasons for differences in cookability are not known. These may be inherited characteristics or may be induced by environmental differences in places where beans are cultivated, or by the stage of maturity when harvested. Furthermore, cookability is also affected by improper storage conditions, evident in extreme hardening of the shell and cotyledons.

FIG. 7. Protein distribution in diet(%)

The observations that have been made may be summarized as follows.

a. There are differences in cookability among cultivars from the same and different locations, suggesting that environmental and genetic factors are each partially responsible.
b. Recently harvested beans are more easily cooked than stored beans are.
c. Rapid water uptake is indicative of good cooking characteristics.
d. High moisture content, high storage temperature, and long storage time decrease cookability by increasing cooking time, as shown in Fig. 9 for a black-coated bean stored at three different moisture levels for six months. ¹⁴
e. The addition of "salt hydration medium" decreases cooking time.
f. Acidity in bean fat increases with storage time, a factor also enhanced by higher moisture levels in the beans and higher storage temperature.
g. A heat treatment inducing sterility inhibits hardening and reduces cooking time. Some representative results of such a simple technology are shown in Fig. 10. It is evident that nine months of storage induced extreme hardening that could be controlled by application of dry or wet heat for a short time.^15,16
h. Incomplete gelatinization of starch granules in beans resulted from barriers imposed by cell structure.¹⁷

FIG. 8. Nutritional Significance of Bean Protein Quantity and Quality to Cassava-Based Diets

FIG. 9. Effect of Moisture in Beans and Storage Time on Cooking Time of Beans

FIG. 10. Effect of Storage (25°C, 70% Relative Humidity) Time on the Hardness of Cooked (18 Hours Soaking, 20 Minutes Boiling), Untreated and Retort-Treated (15 Psi, 121 C) Black Beans

These observations have suggested that hardening may be the result of:

a. tannin condensation decreasing water permeability;
b. reactions between Ca and Mg and organic compounds under the seed coat;
c. chemical reactions between protein and tannins catalyzed by improper storage conditions;
d. enzymatic reactions under the seed coat;
e. cell structure changes.

The main point is that very little is known about this problem. Studies must be carried out, therefore, because acceptability is as important as nutritive value in these foods that are so widely consumed in diets based on cereal grains and starchy foods.

AGRONOMIC AND GENETIC INFORMATION ON THE NUTRITIVE VALUE OF PROTEIN IN BEANS

As a consequence of the need to approach the problem of bean productivity in an interdisciplinary way, efforts are being made to understand the effects of environment, agricultural practices, and genetic factors on the nutritive value of the protein in beans. The results so far available will be reviewed.

Interactions of Environmental and Genetic Factors on Chemical Composition

There are a number of studies reporting the effects of the interaction between environmental and genetic factors on the chemical composition and nutritive value of common beans.^18-21 Some representative findings are shown in Table 6. Most studies report that environmental factors as a whole and genetic constitution influence yield and affect protein and sulfur amino-acid content. Thus, protein quality is also affected. Various studies on specific cultural practices have attempted to measure their effect on protein quality. The application of NPK fertilizer, N-fixing bacteria, and higher plant density increase yield, but no change in protein quality is obtained. On the other hand, there are indications that P applications and S-Triazine herbicides increase protein and free amino-acid content, but the effects have not been evaluated biologically. Other interesting relationships related to yield and protein content in Phaseolus vulgaris are that protein percentage is negatively correlated with bean yield and seed size, protein yield is positively correlated with bean yield, and total protein is positively correlated with seed weight.^3,20,22 Understanding these relationships should be useful in screening programmes aimed at increasing yield as well as protein percentage. However, it would be highly desirable to test the association of such characteristics with cooking and organoleptic qualities as well.

This whole area requires more detailed study in order to understand the possible effects of environmental and genetic factors and cultural practices on the nutritive value and acceptability of common beans.

Amino-Acid Content

The variability reported for the limiting amino acids is presented in Table 7. This variability is due to genetic and environmental factors and to cultural practices.^18,19,23-30

Legume breeding programmes to increase protein quality, i.e., to select yield cultivars with a high methionine content, have progressed only to the point of establishing the range of variability and determining whether or not the level of amino acid is genetically controlled.

TABLE 6. Summary of Results Reported on the Effects of Environmental and Genetic Factors on Various Legume Grains

TABLE 7. Reported Range in Levels of Limiting Amino Acids (mg/g N) of Legume Grains

Source: Reference 18.

Collections from a number of a samples of Central American Phaseolus vulgaris beans have been analyzed and the results studied, as shown in Fig. 11.31 There is a normal distribution of protein, as well as of methionine, cystine, and lysine percentages. From information of this nature, relationships among nutrients have been established, as summarized in Table 8. Both sulfur amino acids, individually or combined, are negatively related to protein content in Vigna and Phaseolus. Of interest is the positive significant correlation between total sulfur and total sulfur amino acids. However, from the available information, the biological value relationships are not clear, as is shown in the lower part of the table. Protein quality should follow chemically determined relationships. Furthermore, even chemically derived data may not give clear relationships, as shown in Table 9 for a study of 127 cultivars of Phaseolus vulgaris. These data show that only cystine is negatively related to protein in ail beans, as a whole or by colour.

TABLE 8. Statistically Significant Relationships between Protein and Sulfur Amino Acids, Total Sulfur and Protein Quality

N = Negative
P = Positive

Methionine and protein, and lysine and protein, were negatively related to protein to a significant degree. Finally, positive correlations have been reported between pairs of amino acids, which suggests that selection for one results in increases in the other. This finding must be confirmed because it may be useful as a selection tool, particularly if analytical techniques are easier to use with one amino acid than with another.

There are two possible ways to attain higher protein quality. One would be to establish whether or not sulfur amino acids are genetically controlled as such, and the other would be to establish whether genes regulate individual protein distribution in legume grains, thereby permitting selection for those proteins higher in sulfur amino acids. Evidence favouring this last approach has already been provided by various workers. Of particular interest are the findings in peas, where protein quality could be predicted from the albumin content, or from a lower globulin-to-albumin ratio, as the latter is a richer source of methionine than the globulins are. Another possibility would be to select for a higher content of alcohol-soluble proteins, which represent about 10 per cent of the total protein. This fraction is also higher in sulfur amino acids.

TABLE 9. Relationships Among Protein and Methionine, Cystine, and Lysine in 127 Cultivars of Phaseolus vulgaris*

*From Central America
NS = not significant
S = significant

Finally, chemical relationships should be reflected in biological assays, but this is not always the case, as suggested earlier. The reasons may be several, such as effect of cooking and subsequent dehydration which, if not carried out under controlled conditions, may decrease amino-acid availability. Other possible reasons are the presence of factors such as tannins, the stage of maturity at harvest, and even possible differences between crude and true protein content.

As is the case with other nutrients, the need for research in this area includes improvement in the chemical and in vitro methodology for determining amino-acid content and availability, especially in the total sulfur amino acids. It is believed that many more studies will be required in order to establish clearer relationships than those shown when comparing chemical characteristics with biological ones.

CONCLUSIONS

A significant amount of work is being carried out today on problems related to increasing legume grain productivity. However, because of the important nutritional role these large groups of staples play in human diets, it is also necessary to explore ways to improve their nutritional and technological properties. It is important to learn more about the interactions among environmental factors, cultural practices, and genetic make-up and their effects on protein and amino-acid content, particularly with respect to the limiting amino acids. Current information from chemical measurements indicates that these factors all influence nutritional value. Protein digestibility is also a problem of importance, as it is necessary to achieve increased availability of the nutrients stored by the plant in the seed. Studies are also needed to obtain more knowledge about the relationship between chemical measures of nutrient quality and biological data on nutritive value. Finally, in yield production programmes, attention should be given to improvement of technological properties, including desirable cooking qualities, consumer acceptance qualities, and the preservation of these attributes during storage.

FIG. 11. Distribution of Nitrogen, Methionine, Cystine, and Lysine in Phaseolus vulgaris (Central America)

References

1. R. Bressani, LG. Elias, M. T. Huezo, and J.E. Braham, "Estudios sobre la produccción de harina precocida de frijol y caupí, solos y combinados mediante cocción-dehisdratación," Arch. Latinoamer. Nutr., 27: 247 260 (1977).

2. R. Bressani, L.G. Elias, and A.T. Valiente, "Effect of Cooking and of Amino Acid Supplementation on the Nutritive Value of Black Beans (Phaseolus vulgaris)," Brit. J. Nutr., 17: 69 (1963).

3. R. Bressani, L.G. Elias, and M.E.F. de España, "Estudio sobre las posibles relactiones entre medidas físicas, químicas y nutricionales en Phaseolus vulgaris," INCAP, Annual Report, 1977.

4. R. Bressani, E. Marcucci, C.E. Robles, and N.S. Scrimshaw, "Nutritive Value of Central American Beans," I. "Variation in the Nitrogen, Tryptophan, and Niacin Content of Ten Guatemalan Black Beans (Phaseolus vulgaris, L.) and the Retention of the Niacin after Cooking," Food Res., 19: 263 - 268 11954)

5. "FAD/WHO Energy and Protein Requirements," report of a Joint FAD/WHO Ad Hoc Expert Committee, WHO Technical Report Series No. 522 (WHO, Geneva, 1973).

6. J.E. graham, R.M, Vela, R. Bressani, and R. Jarquin, "Efecto de la cocción y de la suplementación con aminoácidos sobre el valor nutritivo de la proteina del gandul (Cajanus cajan)," Arch. Venez. Nutr., 15: 19 - 32 (1965).

7. L.G. Elias, D.G. de Fernandez, and R. Bressani, "Studies on the Possible Effects of Seed Coat Pigments of Beans on the Nutritional Quality of Its Protein," submitted for publication, J. Food Sci.

8. R. Bressani, D.A. Navarrete and L.G. Elias, "Calidad protenínica del frijol común y del soya en adultos jóvenes," INCAP, Annual Report, 1977.

9. D.A. Navarrete, L.G. Elias, and R. Bressani, "Estudios sobre la digestibilidad del frijol en humanos," INCAP, Annual Report 1977.

10. Asian Vegetable Research Development Center (AVRDC), Progress Report, 1976. "Report on Mixtures of Mungbeans, Rice and Variability in Methionine Content," Mungbeans, pp. 61 - 67, AVRDC, Taiwan.

11. R. Bressani and A.T. Valiente, "All-Vegetable Protein Mixtures for Human Feeding," VII. "Protein Complementation between Polished Rice and Cooked Black Beans," J. Food Sci., 27: 401 406 (1962)

12. R. Bressani, "Objetivos nutricionales tentativos dirigidos al fitomejorador pare el mejoramiento de alimentos básicos," Arch. Latinoamer. Nutr., 27 (2): 97 - 117 (1977).

13. R. Bressani, A.T. Valiente and C. Tejada, "All-Vegetable Mixtures for Human Feeding," VI. "The Growth-Promoting Value of Combinations of Lime-Treated Corn and Cooked Black Beans,"J. Food Sci., 27: 294 (1962).

14. E.S. de Freitas de Ruiloba, "Efecto de diferentes condiciones de almacenamiento sobre las caracteristicas físico-químicas y nutricionales del frijol (Phaseolus vulgaris)," thesis, CESNA, INCAP, 1973.

15. M.R. Molina, G. de la Fuente and R. Bressani, "Interrelationships between Storage, Soaking Time, Cooking Time, Nutritive Value, and Other Characteristics of the Black Beans (Phaseolus vulgaris)," J. Food Sci. 40: 587 - 591 (1975).

16. M.R. Molina, M.A. Baten, R.A. Gomez Brenes, K.W, King and R. Bressani, "Heat Treatment: A Process to Control the Development of the Hard-to-Cook Phenomenon in Black Beans (Phaseolus vulgaris)," J. Food Sci, 41: 661- 666 (1976).

17. E. Varriano-Marston and E. de Omance, "Effects of Sodium Salt Solutions on the Chemistry and Morphology of Black Beans (Phaseolus vulgaris)," J. Food Sci., 44: 531 - 536 (1979).

18. J.F. Kelly, "Increasing Protein Quantity and Quality," in Nutritional Improvement of Food Legumes by Breeding, M. Milner (ed.), published by the Protein Advisory Group of the United Nations System, United Nations, New York, 1973.

19. O.B. Tandon, R. Bressani, N.S. Scrimshaw and F. Le Beau, "Nutritive Value of Beans: Nutrients in Central American Beans," J. Agric. Food Chem., 5: 137 - 142 (1957).

20. O.I. Leleji, M.H. Dickson, L.V. Crowder and J.B. Bourke, "Inheritance of Crude Protein Percentage and Its Correlation with Seed Yield in Beans, Phaseolus vulgaris L." Crop Sci., 12: 168 - 171.

21. H.C. Murray, S. Kellenbarger and G.A. Armbruster, "Protein Efficiency and Methionine Content of Alaska Peas Grown with the Use of Various Fertilizers," Argon. J., 44: 252- 253 (1952).

22. M.L. Ortega, C. Rodriguez and E. Hernandez X., "Análisis bioquímico exploratorio de granos de los genotipos de Phaseolus vulgaris L. y P. coccineus cultivados en Mexico," Fitotecnia Latinoamericana, 10: 70 - 74 (1974).

23. M.W. Adams, "On the Quest for Quality in the Field Beans," in Nutritional Improvement of Food Legumes by Breeding, M. Milner (ed.), published by the Protein Advisory Group of the United Nations System, United Nations, New York, 1973.

24. M.T. Evans, D. Boulter, R.L. Fox and B.T. Kang, "The Effect of Sulphur Fertilizers on the Content of Sulpho-Amino Acids in Seeds of Cowpea ( Vigna unguiculata)," J. Sci Food Agric., 28: 161 - 166 (1977).

25. F.A. Bliss, "Cow Peas in Nigeria," in Nutritional Improvement of Food Legumes by Breeding, M. Milner (ed.), published by the Protein Advisory Group of the United Nations System, United Nations, New York, 1973.

26. M.T. Evans and D. Boulter, "Chemical Methods Suitable for Screening for Protein Content and Quality in Cowpea (Vigna unguiculata) Meals,"J Sci Food Agric., 25: 311- 322 (1974).

27. S. Bajaj, O. Mickelsen, L.R. Baker and D. Markarian, "The Quality of Proteins in Various Levels of Peas," Brit. J. Nutr., 25: 207 212 (1971).

28. S. Bajaj, O. Mickelsen, H.A. Lillevik, L.R. Baker, W.G. Bergen and J.L. Giel, "Prediction of Protein Efficiency Ratio of Peas from Their Albumin Content," Crop Sci, 11: 813 - 815 (1971).

29. M.H. Dickson and L.R. Hackler, "Protein Quantity and Quality in High-Yielding Beans," in Nutritional Improvement of Food Legumes by Breeding, M. Milner (ed.), published by the Protein Advisory Group of the United Nations System, United Nations, New York, 1973.

30. F.A. Bliss and T.C. Hall, "Food Legumes: Compositional and Nutritional Changes Induced by Breeding," Cereal Foods World, 22: 106 - 713 (1977).

31. R. Bressani, L.D. Hasbun and L.G. Elías, "Contendido de nitrógeno, metionina, cistina, y lisina de cultivares de frijol (Phaseolus vulgaris) de Centro America," unpublished data, 1970.

Contents - Previous - Next