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It is generally known that germination markedly improves the nutritional quality of legumes. A dramatic increase in ascorbic acid in legume seeds has been observed during germination. Also, the concentration of a number of other vitamins is high in germinated legume seeds.
Various attempts have been made to study the effect of germination on the reduction of antiphysiological factors and changes in the organic constituents of legumes in order to improve their nutritive value, but contradictory results are reported in the literature, particularly with respect to protein quality. Most of the reports on the subject indicate that trypsin inhibitor activity is retained in germinated food legumes without affecting nutritive value, an observation deserving more research. Likewise, starch is broken down and both flatulence factors and polvphenolic content are reduced (21-28).
Results of the effects of germination on the protein quality of chick peas are shown in Table 7 as one example (29). Germination did not affect protein quality significantly, although there was a small increase in digestibility. This should have led to an increase in protein quality, but it did not occur because bean protein is deficient in sulphur amino acids. interestingly, trypsin inhibitor activity did not decrease with germination time; however, this did not affect protein quality. On the other hand, prolonged germination causes a significant decrease in the nutritive value of common beans (30), as shown in Table a. Protein efficiency ratio decreases significantly after three days of germination, with a very low value after nine days, reflecting a decrease in total sulphur amino acid content, since apparent protein digestibility showed no major changes until the end of the germination period. Although not shown in this table, protein solubility in 0.01 N NaOH decreased during germination, whereas it increased in the fraction extracted with 5 per cent KCI. Protein solubility in water and in 70 per cent ethyl alcohol remained practically unchanged. The latter should be the object of further investigation, since available amino acid composition will depend on the protein fraction that prevails at different satages of the germination period, the probable reason for the controversial results reported.
FIG. 5. Limiting Nutritional Factors of Common Beans
TABLE 6. Effect of Cooking Food Legumes by Autoclaving, Drum-Drying, and Extrusion on Rat Growth
|Autoclave||Wt. gain,g*.||41.00±6.80||44.00 ± 4.20|
|PER||2.33±0.18||1.47 ± 0.09|
|Drum-drying||Wt. gain, g*||28.00±0.40||52.00 ± 2.60|
|Extrusion||Wt. gain, g*||48.00±4.90||75.00±5.20|
* 28 days
Source: Reference 20.
TABLE 7. Effect of Germination on the Nutritive Value of Chickpea for Rat Growth
|2-day germination, raw||30||3.58±0.41||3.05||75.1±1.5|
|2-day germination, boiled||30||3.86±0.37||2.72||80.0±2.5|
|4-day germination, raw||28||3.60±0.32||3.60||78.0±1.5|
|4-day germination, boiled||34||3.67±0.26||1.03||82.4±2.0|
Source: Reference 29.
TABLE 8. Changes in the Nutritive Value for Rat Growth of Common Beans (Phaseolus vulgaris) during Germination
Processing food by fermentation has been practiced by man for centuries and has been used quite extensively in various parts of the world, particularly in the Orient. The number of foods that normally undergo fermentation is relatively high, and there are obviously many changes in chemical composition and nutritive value, all well documented. Some general observations made by different workers on the effects of fermentation on nutritive value include increases in B12 as well as in other vitamins of the B group. Likewise, there are increases in protein quality, increased availability of various nutrients, and removal of antiphysiological factors. Of particular significance is the supplementary effect induced by microbial growth on a substrate (31). Although fermentation is usually carried out on the food legume itself, from the nutritional point of view, fermentation of mixtures of legumes and cereal grains have attractive possibilities, as shown in Table 9 (32).
A mixture of soybean and wheat in a ratio of 60:40 provides protein of a quality higher than that of either one alone (33). if these foods individually or combined are fermented through the use of micro-organisms such as Rhizopus oligosporus, there are important increases in protein quality, as shown in the table. The fermented product in every case showed a higher protein quality, depending on the inherent protein quality of the food before fermentation. For example, wheat protein quality increased much more than that in soy because the protein of the micro-organisms contains Iysine, which is deficient in wheat, and both micro-organisms and soy protein are deficient in methionine. The point is that fermentation offers very good opportunities to develop foods of higher quality (32).
Finally, fermentation processes using solid substrates have been considered as an attractive alternative for the production of new sources of protein foods in the underdeveloped countries.
TABLE 9. Weight Gain, Food Consumption, and Protein Efficiency Ratio in Rats Fed Fermented or Unfermented Grains as Protein Sources
|Wheat (control)||37.6±2.7||295 ±13||1.28±0.05|
|Wheat (fermented)||55.0±1.6***||322 ±7**||1.71±0.05|
|Soybeans (control)||76.5±2.3||353 ±10||2.17±0.03|
|Soybeans (fermented)||72.9±3.3||321 ± 12**||2.27±0.05|
|Soybean/wheat (control)||97.1±3.2||389±8||2.49± 0.04|
**Significantly different (P <0.05j from corresponding unfermented grain Source: Reference 32.
STORAGE OF PROCESSED FOOD LEGUME PRODUCTS
Processed bean products include canned beans as well as powders. However, studies on the effect of storage on nutritive value are few. Improperly stored powders become damaged rather easily; one example for soybean flour is shown in Table 10. In this case soybean meal, after delivery to the port of entry, was stored at the unloading site for about four months before transfer to the feed mill.
TABLE 10. Effect of Storage on the Nutritive Value of Soybean Meal.
* INCAP, unpublished data
Samples, classified by colour, were taken for chemical and biological analysis with the results shown in the table. Available Iysine was acceptable in the light-coloured samples, but it was significantly low in the dark-coloured ones. The loss in available Iysine was reflected in the evaluation of protein quality by the NPR procedure, the data showing a significant difference in protein quality (INCAP, unpublished data). This type of deterioration has been reported in other food products, particularly in milk powder, often shipped by developed to developing countries for distribution in supplementary feeding programmes. Losses in food quality through improper handling and storage obviously have significant economic and nutritional implications that may be reduced or eliminated by improving storage conditions. Similar observations have been made with bean powders produced by moist cooking in an autoclave followed by dehydration and storage in paper and polyethylene bags at ambient temperature. Prolonged storage resulted in increased free fatty acid content and reduced feed intake in biological trials because of decreased protein quality in the product (34-.
OTHER PROCESSING PROBLEMS WITH COMMON BEANS
Recently, the results of various studies have indicated that common beans contain polyphenolic compounds that interfere with protein digestibility and protein quality (35), as indicated in Figure 6 (36-. The fate of such compounds during cooking has been studied The results shown in Figure 7 indicate an initial drop during the first 15 minutes of cooking, with the value remaining stable for up to 60 minutes. The values then increase slightly and remain constant. The increase is attributed to an uptake of tannins by the beans from the cooking liquor, since as cooking time progresses the cooking water is partially absorbed by the beans. On the other hand, trypsin inhibitors drop continuously to zero values at 90-minutes cooking time at atmospheric pressure. The cooking water contains polyphenolic compounds and the value in that fraction at the end of 150 minutes is also shown in the figure. It amounted to 0.42 g catechin equivalent/100 g. Analysis of polyphenolic compounds in raw and cooked bean samples, taking into consideration the content in the remaining cooking water, showed that large losses in trypsin inhibitors had taken place.
FIG.6. Relationship between Polyphenolic Content (Catechin Equivalent) in Raw and Cooked Beans (Phaseolus vulgaris) and Apparent Protein Digestibility in Adult Humans
FIG. 7. Changes in Catechin Equivalent and in Trypsin Inhibitors during Cooking of Common Beans
In other experiments the partition of polyphenolics has been studied (Table 11) (36). The upper part of the table shows the values in the fraction analysed, while in the lower section the values represent percentage distribution. The figures show that, of the total polyphenolics in raw beans expressed as tannic acid, 60.4, 66.7, and 37.4 per cent remained in black, white, and red beans, respectively, after cooking. The cooking liquid contained 19.1, 15.5, and 11.7 per cent of the total. If no destruction of tannins takes place, it may be assumed that 20.5, 17.8, and 50.9 per cent of the total become bound. Thus, the differences- in the apparent loss when polyphenolics are expressed as tannic acid or as catechin equivalent may be because the tannic acid indicates the amounts that became bound. Bound tannins would be those polyphenolic compounds not measured by current analytical methods, since they have reacted with amino groups of the protein and are thus not extracted by methanol, which would be responsible for the decrease in protein digestibility. An important consideration in understanding the effect of polyphenolic compounds on digestibility is to establish the fate and role of them compounds during cooking, an area that should receive increased attention, including improved analytical techniques for such compounds.
TABLE 11. Partition of Polyphenolic Compounds in Beans upon Cooking
||White g/500 g||Red|
A second problem is related to the possible presence in beans of proteins resistant to enzymatic action even after "appropriate cooking". This fraction found in cooked beans decreased protein digestibility, as shown by the reggression equation in Figure 8. In this case the alkali-soluble fraction in cooked beans, amounting to 9 to 20 per cent of the total, negatively influenced protein digestibility in rats. Similar results have been obtained in dogs (37), and even more important, in human studies (38), in which a negative correlation (Y = 95.81 - 1.17 X, r. = 0.94 was also found. This is another area that deserves additional research. Thus, the nutritional potential of bean protein is diminished by these two factors.
FIG. 8. Relationship between Salt-Soluble Proteins in Cooked Beans and Their True Protein Digestibility
The above discussion presented a number of examples of the effects of storage and processing on the nutritional value of food legumes, with emphasis on common beans. Although the conditions leading to the hard-to-cook phenomenon are relatively well established, it is important to understand the biochemical mechanism catalysed by such storage conditions so as to develop practical ways to ret duce or inhibit the process. Likewise, chemical components responsible for resistance to insect attack should be determined to minimize physical losses of products and reduce losses in nutritive value. With respect to processing, various methods can be used to make food legumes edible and to obtain the maximum nutritive value possible from its chemical composition.
Improper processing may lead to products still containing antiphysiological substances and protein structures resistant to hydrolysis and utilization. Although the usual carbohydrate/protein interactions probably reduce nutritive value, the role of other substances such as polyphenols should be established.
Additional aspects of a chemical and biochemical nature must be further studied in order to improve the utilization and consumption of legume foods. For processing reasons, the prolonged cooking time of dehulled beans, and the improved protein utilization of beans processed by extrusion must be investigated. Identification of changes in the carbohydrate fractions in raw and processed legumes, as well as determination of the protein solubility pattern during germination must be attempted. Chemical methods for polyphenol identification and quantitative determination and analysis are urgently needed.
Finally, there should be strong interactions among chemists, geneticists and plant breeders, food scientists and technologists, and nutritionists to upgrade the nutritional potential of food supplies, especially of legumes.
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5. R. Bressani, "Research Needs to Up Grade the Nutritional Quality of Common Beans (Phaseolus vulgaris)." In: Proceedings of the Workshop, Current Aspects on Legumes as a Foord Constituent with Special Emphasis on Lupines, San Diego California, August 1981 (in press, 1982).
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15. R. Bressani, L. G. Elías, and R. Gómez Brenes, "Valor Proteínico del Haba (Vicia faba) y su Utilización en Sistemas de Consumo Alimentario para Seres Humanos." INCAP Annual Report (1981), p. 72.
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17. M.R. Molina, G. de la Fuente, and R. Bressani, "Interrelation-ships between Soaking Time, Cooking Time, Nutritive Value and Other Characteristics of the Black Bean (Phaseolus vulgaris)." J. Food Sci. 40: 587 (1975).
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19. G. Tobin and K.J. Carpenter, "The Nutritional Value of the Dry Bean (Phaseolus vulgaris). A Literature Review." Nutr. Abstr. Rev. 48:919 (1978).
20. R. Bressani, LG. Elías, M.T.Huezo, and J.E.Braham "Estudios sobre la Produción de Harinas Precocidas de Frijol y Caupí, Solos y Combinados mediante Cocción-Deshidratación." Arch. Latinoamer. Nutr. 27: 247 (1977).
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24. ALL. Kakade and R.J. Evans, "Effect of Soaking and Germination on the Nutritive Value of Navy Beans." J. Food Sci. 31: 781 (1966).
25. I. Noor, R. Bressani, and LG. Elías "Changes in Chemical and Selected Biochemical Components, Protein Quality and Digestibility of Mung Bean (Vigna radiata) during Germination and Cooking." Qual. Plant Foods Hum. Nutr. 30: 235 (1980).
26. U. Chandrasekhar and K. Jayalakshmi, "Evaluation of Protein Quality of Sprouted Roasted and Autoclaved Legumes on Albino Rats." Indian J.Nutr. Diet. 15: 414 (1978).
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29. A. Khaleque, L.G. Elías, J.E. Graham, and R. Bressani, "Studies on the Development of Infant Foods from Plant Protein Sources. Part 1 Effect of Germination of Chickpea (Cicer arietinum) on the Nutritive Value and Digestibility of Protein " J. Sci. Food Agric., in press (1982).
30. L.G. Elías, A. Conde, A. Muñoz, and R. Bressani, "Effect of Germination and Maturation on the Nutritive Value of Common Beans (P. vulgaris)." In: Nutritional Aspects of Common Beans and Other Legume Scads as Animal and Human Foods, W.G. Jaffe'(Ed.). Proceedings of a Meeting Held Nov. 6-9, 1973, Ribeirao Preto, S.P. Brasil (pp. 139-152).
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32. Hwa L. Wang, D.l. Ruttle, and C.W. Hesseltine "Protein Quality of Wheat and Soybean after Rhizopus oligosporus Fermentation." J. Nutr. 93: 109 (1968).
33. R. Bressani, "Complementary Amino Acid Patterns." In: Nutrionts in Processed Foods, Proteins P.L. White and D.C. Fletcher (Eds.) for American Medical Association. (Publishing Sciences Group, Inc., Acton, Massachusetts, 1974, pp. 149-166).
34. L.G. Elías, R. Bressani, and M. Flores, "Los Problemas y los Potenciales en el Almacenamiento y Procesamiento de los Leguminosas de Grano Comestibles en América Latina." In: Seminario "El Potencial del Frijol y de Otras Laguminosas de Grano Comestibles on América Latina" Feb. 26- Mar. 1 1973, Cali, Colombia (CIAT, Cali, Colombia, 1973, pp. 32-48).
35. R. Bressani and LG. Elías, "The Nutritional Role of Polyphenols in Beans." In: Poliphenols in Careals and Legumes, J.H. Hulse (Ed.) (IDRC-145e, IDRC, Ottawa, Canada, 1979).
36. R. Bressani, L.G. Elías, and J.E. Braham, "Reduction of Digestibility of Legume Protein by Tannins." In: Workshop on Physiological Effects of Legumes in the laymen Diet, XII International Congress of Nutrition, San Diego, California, August 1981 (in press, 1982)
37. R. Bressani, L.G. Elías and M.R Molina, "Estudios sobre la Digestibilidad de la Proteína de Varias Especies de Leguminosas". Arch. Latinoamer. Nutr. 27: 215 (1977).
38. R. Bressani, E. Hernández, D. Navarrete, and J.E. Braham "Protein Digestibility of Common Beans (Phaseolus vulgaris) in Adult Human Subjects" (in press, 1982).
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