Factors Influencing Nutritive Value in Food Grain Legumes - iBrarian

Factors Influencing Nutritive Value in Food Grain Legumes: Mucuna Compared to Other Grain Legumes

Factors Influencing Nutritive Value in Food Grain Legumes: Mucuna Compared to Other Grain Legumes R. Bressani1

Abstract This paper discusses the nutritional characteristics of food grain legumes –mainly Phaseolus vulgaris– and compares it to information available on Mucuna. The review suggests that Mucuna is very much like P. vulgaris and other grain legumes with respect to chemical composition, micronutrient content, amino acid values, nutritional and biological quality, and content of antinutritional substances with the exception of the compound L-Dopa (3,4-dihydroxy-L-phenylalanine) present in Mucuna beans. A limited number of studies all indicate that various types of processing techniques alone or combined with others could, to a large degree, render Mucuna beans free of adverse L-Dopa effects and useful in providing adequate nutrition to people. Studies on Mucuna processing should be expanded and the products obtained should be evaluated biologically. Likewise, studies should be conducted to determine the acceptability characteristics of Mucuna beans to the consumer.

1. Introduction It is a well-recognized fact that food grain legumes, such as common beans, lentils and kidney beans, represent the main supplementary protein 1 Centro de Ciencia y Tecnología de Alimentos, Instituto de Investigaciones, Universidad del Valle de Guatemala, Guatemala.

164

FOOD AND FEED FROM MUCUNA: CURRENT USES AND THE WAY FORWARD

source in cereal and starchy food-based diets consumed by large sectors of the population living in developing countries. Not only is the nutritional value of these legumes of great importance, their intake is unfortunately lower than what is desirable. Furthermore, food grain legumes should be free of anti-physiological substances, have high nutrient bioavailability and be easily processed into edible, acceptable products. Factors that determine bean grain quality may be divided into two large categories: those related to acceptability to the consumer, and those associated with nutritive value (Table 1) (Bressani, 1989, 1993). The point of view of consumers is key to defining acceptability characteristics of the raw grain and its processed forms. But such characteristics are very difficult to determine and controversial to measure since they depend to a large extent on subjective characteristics associated with cultural behavior and patterns among different populations. Studies are, however, being conducted in this Table 1. Quality components of food grain legumes. Acceptability components Physical factors - seed appearance, color, flavor, size Texture Cooking time Food products Positive nutritional components Nutrition-related High protein content High lysine content Health-related Dietary fiber Negative nutritional components Antinutritional factors Enzyme inhibitors, lectins, flatulence factors, tannins, phytic acid, saponins, others Nutrition related Protein digestibility, sulfur amino acid deficiency, carbohydrate bioavailability Source: Bressani, 1989

165


area, particularly in relation to the hard-to-cook characteristic true of most food legumes, including common beans. Of all acceptability characteristics, the hard-to-cook defect is without doubt the most important (Bressani, 1993a; El-Tabey Shehata, 1992; Hincks and Stanley, 1986). For common beans, additional acceptability attributes include the thickness of the soup, the cohesiveness of fried beans, and particle size and color of the products. The integrity of the bean after cooking is of importance in industrial applications and possibly also at the household level (Bressani, 1993a). Acceptability data on Mucuna beans are not available but should be obtained to help better use this grain legume as food or feed. The nutritional value of food grain legumes, not always fully understood and appreciated by consumers, is divided here into two large groups: positive and negative factors. The positive factors include high protein and lysine content, which allows legumes to serve as excellent protein supplements to cereal grains (Bressani, 1989, 1993). The health-related value of beans includes their positive effect on blood cholesterol and glucose levels (Walker, 1982; Leeds, 1982), possibly through the dietary fiber present in beans. The negative factors fall into two groups. Antinutritional factors include enzyme inhibitors, hemagglutinin, flatulence factors, polyphenols, tannin and phytic acid. The negative nutritional factors include protein and carbohydrate digestibility, and sulfur amino acid deficiency (Bressani, 1989, 1993). In the following review, attention is given to some of the chemical, biological and nutritional information available for Phaseolus vulgaris, a food grain legume of high preference by the Latin American population, as well as other grain legumes. This information is compared to that available on Mucuna beans in order to highlight gaps in our knowledge and to suggest factors in Mucuna that may be limiting its wider and more efficient use as food and feed.

166


2. Nutritive Value: Mucuna in Comparison to Other Legumes Mucuna beans have been used more as a cover crop than as a foodsource for humans. This may explain in part why culinary practices associated with Mucuna are still poorly developed, why acceptability of the bean is limited, and why chemical and nutritional information is yet forthcoming in comparison to that available for other edible grain legume crops of economic significance. Even so, people in different countries of Asia and Africa have been consuming Mucuna, regardless of their knowledge of its possible deleterious effects. Consequently, it is very important to increase our knowledge about the acceptability characteristics, nutritive value and food safety of Mucuna beans. 2.1. Positive Factors For populations living in developing countries, food grain legumes represent foods that provide protein not unlike what meat and cheese do for those in the developed world. Because of their high protein and lysine content, they also represent good sources of supplementary protein when added to cereal grains and root crops, which are low in protein and lysine. Furthermore, grain legumes contain high levels of dietary fiber and phytochemicals (phytonutrients), which may be closely associated with health promotion. 2.1.1. Nutritional Component As already indicated, the positive nutritional components in food grain legumes include relatively high protein and available lysine content (see Table 2 regarding the protein and lysine content of food grain legumes consumed in Latin America, including Mucuna). Although not shown in the table, the protein content of legumes other than Mucuna varied from 18 to 44% on a dry weight basis, a relatively high variability for each spe167


cies. Each of the species studied contained around 65% carbohydrate, with the exception of lupins, soybeans and peanuts, each of which contained high levels of fat. The protein content of Mucuna beans varied between 23 and 35% and is therefore similar to that of other food grain legumes (Dako and Hill, 1977; Kay, 1979; Laurena et al., 1991; Mary Josephine and Jonardhanan, 1992; Siddhuraju et al., 1996; Vijayakumari et al., 1996). This level of protein is of nutritional significance since moderate intake of beans will greatly increase total dietary protein intake. The values for lysine range from 325 to 492 mg g-1 N for all samples (Table 2). However, as with protein content, the variability for each species may be high. Peanut protein is an exception for grain legumes with a low lysine value of around 223 mg g-1 N. Lysine values for Mucuna beans vary from 327 to 412 mg g-1 N (Laurena et al., 1991; Mary Josephine and Table 2. The protein, lysine and sulfur amino acid content of grain legumes. Common name

Scientific name

Protein (%)

Common bean Caraota Cow pea Pigeon pea Chick pea Peas Faba beans Kidney beans Lentils Tepary Dolichos Canavalia Lupinus Soya Peanuts Mucuna FAO/WHO

P.vulgaris P. coccineus V. sinensis C. cajan C. arietinum P. sativum V. faba P. lunatus L. esculenta P. acutifolius D. lablab C. ensiformis L. mutabilis G. max A. hypogaea Mucuna species Ref. Pattern

22.0 22.8 24.1 19.2 18.2 22.5 24.0 22.3 23.7 23.2 22.1 25.4 44.3 33.4 26.7 23-35 -

168

Lysine (mg gN-1) 464 470 407 451 431 458 351 408 382 428 492 457 325 395 223 327-412 360

Total sulfur amino acids (mg gN-1) 125 179 177 161 172 156 70* 179 96 144 224 85* 152 195 149 116-132 220


Janardhanan, 1992; Rajaram and Janardhanan, 1991; Siddhuraju et al., 1996) which is 91-114% of the reference WHO/FAO standard (WHO/FAO, 1973). The high lysine content of grain legume protein is a very important nutritional attribute, and probably more important than total protein content because it makes food grain legumes a significant supplementary protein to cereal grain-based diets, which are known to be deficient in lysine. The supplementary effect for various cereal grains and food legumes can be seen in Figure 1. In general, protein quality is high when cereals are fed with grain legumes in a weight ratio of 7-8 parts cereal to 3-2 parts beans. This ratio has been derived from experiments with animal and human subjects Figure 1. Protein quality of cereal grain/food legume mixtures. 3 Rice/Common beans

Net Protein Ratio

2.5 Rice/Chickpeas 2 Wheat/Fava beans 1.5 Corn/Common beans 1

0.5

0 0/100

25/75

50/50 Cereal/Grain legume, %

75/25

100/0

Source: Bressani, 1993a, 1993b.

169


(Bressani, 1989, 1993a). Data on mixtures of Mucuna beans with cereal grains are not available. But based on its high lysine content we would expect a similar response. In these cereal-legume mixtures, cereals supply sulfur amino acids, which generally are low in legumes, thus further improving the balance of essential amino acids. The mineral content of food grain legumes is of interest from the point of view of nutrition but also, in respect to the hard-to-cook problem, because of effect that some minerals have on the cooking process. Table 3 summarizes some information on the mineral composition of P. vulgaris (Augustin et al., 1981) and Mucuna as published by various authors (Mary Josephine and Janardhanan, 1992; Rajaram and Janardhanan, 1991; Ravindran and Ravindran, 1988; Siddhuraju et al., 1996). The levels of minerals in Mucuna vary considerably, yet are similar to those found in Phaseolus. The relatively high level of potassium (K) in Mucuna and Phaseolus is especially noteworthy. Iron content is of special interest because of its deficiency in the diets of many in developing countries, particularly among rural dwellers. -1

Table 3. 1

, ,

170

2

3

4

5


2.1.2. Health-related components Various studies conducted with P. vulgaris and other grain legumes have shown that beans, when consumed, reduce plasma cholesterol levels and slowly increase blood glucose levels (Leeds, 1982; Walker, 1982). These effects have been associated with the dietary fiber fraction in beans. Table 4 presents data on insoluble dietary fiber (neutral detergent fiber) in various food grain legumes. In addition, the table shows values reported for Mucuna, with NDF varying in Sri Lanka from 17.7 – 21.8 g.100 g-1 with an average of 20.45 ± 0.7 g.100 g-1 (Ravindran and Ravindran, 1988); the ADF and NDF values for the sample from Guatemala are lower. In general, the differences in ADF and NDF between Mucuna and other grain legumes are small and, therefore, Mucuna bean intake will possibly have positive effects in the control of plasma cholesterol and blood glucose levels. It should be pointed out that cooking of grain legumes increases the dietary fiber, particularly in the insoluble fraction. And too much of an increase may not be desirable, considering the binding effects of fiber on a number of nutrients, and particularly minerals.

Table 4. Fiber fractions in various grain legumes (g 100g-1) (dry weight basis). Component

Canavalia ensiformis1

Acid detergent fiber (ADF) Neutral detergent fiber (NDF) Hemicellulose Cellulose Lignin

11.0 13.6 2.6 8.1 2.9

Cajanus cajan1 9.1 15.1 6.0 6.9 2.2

Vigna sp.1 7.6-7.9 9.5-10.7 1.6-3.1 5.0-5.7 2.2-2.6

Mucuna Guatemala1 utilis2 8.9 14.7 5.8 7.1 1.8

10.4±0.6 20.4±0.7 10.0±0.9 9.3±0.9 0.8±0.06

1 Bressani and Chon (unpublished data). 2 Ravindran and Ravindran, 1988.

171


2.2. Negative Factors Food grain legumes have always been associated with a number of substances which inhibit specific physiological functions of the animal organism, including digestion, enzyme activity, and metabolism and absorption of nutrients. Most of the substances are changed in the process of preparing foods, and cooking is one of the most efficient ways to reduce these compounds. There are other substances, such as sugars, which produce gas and cause much discomfort to individuals who consume grain legumes. In addition, it is well known that grain legume protein is limiting in sulfur-containing amino acids. The addition of 0.2 - 0.3% of these amino acids increases protein quality significantly; however, digestibility is not improved. 2.2.1. Antinutritional Factors The acceptability and use of food grain legumes has been limited by the presence of relatively high concentrations of a number of antinutritional factors, including protease inhibitors (trypsin), a-amylase inhibitors, lectins, polyphenolic compounds, tannins, phytic acid, HCN, flatulence factors, and allergens (Liener and Kakade, 1980; Liener, 1989). These factors negatively affect the nutritive value of beans through direct and indirect reactions: they inhibit protein and carbohydrate digestibility; induce pathological changes in intestine and liver tissue thus affecting metabolism; inhibit a number of enzymes and bind nutrients making them unavailable (Bressani, 1989, 1993). Data for Mucuna beans and other grain legumes are presented in Table 5 (Mary Josephine and Janardhanan, 1992; Rajaram and Janardhanan, 1991; Ravindran and Ravindran, 1988; Siddhuraju et al., 1996;Vijayakumari et al., 1996). Although there are some differences in concentration among the various Mucuna and other legume samples (not shown) (Fernández et al., 1981, 1982; Iyer et al., 1980; Jaffe, 1973; Ologhobo and Fetuga, 1983), the values are not sufficiently different to indicate that 172


Table 5. Antiphysiological substances in grain legumes. Antiphysiological substance

TIA (Protease inhibitor) Amylase inhibitor Lectins Phytic acid Polyphenols Tannins HCN Hydrocyanic acid Flatulence factors: Raffinose Stachyose Verbascose L-Dopa

Food grain legumes + + + + + + + + + + Fava beans Mucuna beans

Mucuna

48.43 units (16.1 mg prot-1m-1)(1) 86.4 units g-1 (5) + (1) 0.31 (3), 0.5.-0.63 (2) g 100g-1 2.07 g 100g-1 (1) 6.14 g 100g-1 (1) 5.8 mg 100g-1 (3) 1.36-1.62 g 100g-1 (2) 1.18-1.24 g 100g-1 (2) 0.96-1.07 g 100g-1 (2) 1.50 g 100g-1 (1) 6.97-9.16 g 100g-1 (4)

(1) Rajaram and Janardhanan, 1991 (2) Vijayakumari et al., 1996 (3) Ravindran and Ravindran, 1988 (4) Mary Josephine and Janardhanan, 1992 (5) Siddhuraju et al., 1996

Mucuna would be of poorer nutritional quality due to antinutritional factors. All grain legumes contain relatively high amounts of sugars responsible for flatulence, and Mucuna is no exception (Table 5). Mucuna is known to contain toxic levels of L-Dopa, which is also found in fava beans though in lower concentrations (Daxenbichler et al., 1972; Liener and Kakade, 1980; Liener, 1989; Mary Josephine and Janardhanan, 1992; Rajaram and Janardhanan, 1991).

173


2.2.2. Antiphysiological Effects Protein Digestibility Table 6, which summarizes digestibility studies conducted on rats, compares the apparent protein digestibility of the main food grain legumes consumed in Latin America (Bressani et al., 1977; Bressani, 1993a) with Table 6. Apparent protein digestibility (A.P.D.) of edible grain legumes in rats. Grain legume

A.P.D. %

Common bean (P. vulgaris)-all colors Runner bean (P. coccineouos) Cowpeas (V. sinensis) Chick pea (C. arietinum) Broad beans (V. faba) Lentil (L. esculenta) Pea (P. sativum) Pigeon pea (C. cajan) Lima beans (P. lunatus) Sweet lupin (L. mutabilis) Jack bean (C. ensiformis) Mucuna

67.4-78.5 68.6 - 72.8 65.0 - 80.2 73.0 - 83.0 77.7 - 83.5 73.7 - 80.3 82.4 - 89.3 59.9 51.3 76.5 - 77.8 76.4 - 78.7 72.19* - 68.5**-81.6**

*

Laurena et al., 1991 Siddhuraju et al., 1995

**

Table 7. Apparent protein digestibility (A.P.D.) of P. vulgaris in human subjects. Bean sample Black Red White 50% Black/50%White Black Cheese Source: Bressani, 1993a.

174

Number of subjects (adults) 12 12 12 12 12 12

A.P.D. % 49.6±10.2 55.7±16.2 62.1±10.1 57.4±9.1 53.4±7.2 76.2±4.9


Table 8. Relationship between tannin (tannic acid) consumption with and without methionine on the protein efficiency ratio (PER) and apparent protein digestibility (A.P.D.) of red P. vulgaris.

Tannin intake, g

Without methionine PER A.P.D. %

0.74±0.14 1.00±0.14 1.12±0.17 0.82±0.09

0.90±0.24 0.66±0.16 0.53±0.25 0.37±0.16

69.2±3.1 71.8±2.3 66.8±4.3 66.6±4.3

With methionine Tannin PER intake, g

A.P.D %

1.33±0.14 1.28±0.11 2.13±0.27 2.03±0.32

69.5±2.8 63.3±9.2 64.9±2.8 66.0±9.6

2.28±0.16 2.28±0.28 1.86±0.18 1.78±0.34

PER = Protein Efficiency Ratio = Average weight gain/protein intake. Source: Braham and Bressani, 1985

Mucuna (Laurena et al., 1991; Siddhuraju et al., 1996). It shows that Mucuna protein digestibility is similar to that of other grain legumes. In general, the large variability evident in Table 6 is of interest since it may suggest that within one species some varieties are more digestible than others. Table 7 (Bressani, 1993a), which summarizes protein digestibility studies conducted in human subjects, shows that digestibility is a problem with Phaseolus and other grain legumes. White beans have the highest digestibility (62.1%) followed by black and red beans (49.6 and 55.7%, respectively).The average protein digestibility of the animal proteins in our study was 76.2%, which is significantly higher. The poor digestibility of the 50%/50% blend of black and white beans, which falls between that of white and black alone, can originate from a number of factors. First, it is probably associated with polyphenolic compounds in the seed coat, which are present in greater amounts in black than in white beans. Second, the low digestibility can also result from increases in dietary fiber during cooking. These issues should be studied in more detail for Mucuna. Finally, Table 8 illustrates that tannins affect protein digestibility and protein quality. As intake of tannins increases, protein quality and protein digestibility of P. vulgaris decreases both in the absence and presence of methionine. Various authors have reached similar 175


conclusions (Aw and Swanson, 1985; Braham and Bressani, 1985; Bressani et al., 1977; Elías et al., 1979). Since Mucuna contains tannins as well, it is expected to affect protein digestibility in a similar negative fashion. Carbohydrate Digestibility Carbohydrate digestibility of grain legumes is often lower than would be expected. This low digestibility may be the result of the high amount of dietary fiber found in beans, which increases during cooking. Grain legumes also contain amylase inhibitors, which are destroyed during cooking. One aspect of importance is water penetration into the cell, which helps to gelatinize the starch. If the cell is not well hydrated, starch will not gelatinize resulting in low digestibility. Large seeds and seeds with an impermeable seed coat tend to have low carbohydrate digestibility. Sulfur Amino Acid Deficiency Table 2 presents the average content of sulfur amino acids for a number of grain legumes. Their content varies from 96 to 224 mg g-1 N. The FAO/ WHO reference value is 220 mg g-1 N, which makes most grain legumes limiting in these amino acids. Values for Mucuna found in the literature vary from 116 to 132 mg g-1 N (Laurena et al., 1991; Mary Josephine and Janardhanan, 1992; Rajaram and Janardhanan, 1991; Siddhuraju et al., 1996), about 53-60% of the FAO/WHO reference (1973), indicating that Mucuna protein is deficient in sulfur amino acids. Table 9 shows the significant improvement in protein quality, which is obtained by adding 0.3% methionine to several food grain legumes (Jaffe, 1950). Since the sulfur amino acid content of Mucuna is low and similar to that of other grain legumes, we would expected protein quality to be improved with supplements of methionine. That this is the case is demonstrated at the bottom of Table 9 (Dako and Hill, 1977). When methionine supplementation reached 0.5%, a high improvement in protein quality was 176


obtained. The usual level of methionine supplementation is 0.3%, if a diet of 10% protein is derived exclusively from cooked beans. This added methionine should theoretically raise the total sulfur amino acid content of the food to the requirement level. However, other factors may play a role in determining actual level of supplementation in biological trials. For example, in one study P. vulgaris beans of black, red and white color were fed to rats at 10% protein and supplemented with up to 0.4% methionine. We observed that white beans gave higher weight gains and Protein Efficiency Ratio (PER) values at lower levels of methionine addition than did black and red beans. This suggests that other factors besides methionine deficiency play a role in the response to sulfur amino acid supplementation (Bressani, 1993). The protein content would be of particular interest for populations that use root crops as their basic diet; also important, however, is the quality of the protein. Improvement in weight performance of growing laboratory rats fed cassava with beans both with and without methionine has been shown. WithTable 9. Protein efficiency ratio (PER) of food grain legumes with and without methionine supplementation. Food grain legume

PER Without methionine

Phaseolus vulgaris (black)* Phaseolus vulgaris (red)* Phaseolus vulgaris (white)* Vigna sinensis (black)* Vigna sinensis (beige)* Pisum sativum (green)* Pisum sativum (yellow)* Lens esculenta* Cicer arietinum* Mucuna pruriens**

0 - 0.9 0 1.2 1.0 1.0 0.3 0 0 1.7 2.3

With methionine 3.5 - 3.8 1.7 2.7 1.6 1.8 2.7 1.2 0.4 2.8 3.6

* Jaffé, 1950. (0.3% Methionine) **Dako and Hill, 1977 (0.5% Methionine)

177


out methionine, a ratio of 15 g of beans to 85 g of cassava was needed to achieve weight equilibrium. However, with methionine the same ratio gave a weight gain of 20 g (Bressani, 1989). The amino acid content of P. vulgaris and Mucuna beans (Kay, 1979; Laurena et al., 1991; Mary Josephine and Janardhanan, 1992; Rajaram and Janardhanan, 1991; Siddhuraju et al., 1996) as well as the FAO/WHO reference pattern is shown in Table 10. As discussed previously, Mucuna Table 10. Amino acid content of P. vulgaris and Mucuna (g 16 g-1 N). Amino acid

Lysine Histidine Arginine Tryptophan Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Cystine Methionine Valine Isoleucine Leucine Tyrosine Phenylalanine

Average P. vulgaris 1 7.74 2.52 5.68 1.14 13.72 4.65 6.28 19.50 3.73 4.10 4.35 1.26 1.27 (2.53)3 5.03 4.03 8.66 2.50 5.50

1 Kay, 1979. 2 Ravindran and Ravindran, 1988. 3 Total sulfur amino acids. Limiting amino acids.

178

Average Mucuna 1 6.60 3.14 7.16 1.35 8.16 3.64 4.10 17.23 5.12 2.81 0.84 1.28 (2.12)3 5.57 4.12 7.85 4.73 3.85

Mucuna utilis 2 6.41 2.23 5.90 ND 8.93 4.18 4.07 14.42 5.25 3.93 3.29 1.86 5.26 4.71 7.18 4.77 5.23

FAO/WHO standard 5.5 1.0 4.0 3.53 5.0 4.0 7.0 6.0


beans seem to contain sufficient amounts of all essential amino acids with the exception of sulfur amino acids (S.A.A.). However, it would be of interest to test whether sulfur amino acids are deficient, and to assess other potential amino acid deficiencies since, in some situations, amino acids may not be amply available.

3. Processing to Improve Nutritive Value and Acceptability In order to make food grain legumes edible, consumers have developed a relatively large number of processing methods. Researches have studied Table 11. Main nutritional effects of processing on grain legumes. 1

Thermic processes with water a. inactivate enzyme inhibitors and lectins b. reduce other antinutrients - tannins c. increase protein and carbohydrate digestibility d. increase protein quality e. excess heat reduces lysine and sulfur amino acid bioavailability f. addition of salts and soaking may reduce protein quality if cooking is not controlled

2

Dry-thermic processes a. extrusion cooking: (high T, short time) induces similar effects as those to cooking with water b. roasting: (high T, long time) decreases nutritive quality

3

Germination and fermentation a. increase vitamin content b. reduce flatulence factors c. other effects controversial (e.g. protein quality)

4

Dehulling and cooking a. increase protein digestibility b. increase protein quality c. decrease tannin content

179


these traditional recipes, as well as some more modern technologies, and the results obtained have helped not only to make the beans more acceptable to consumers but also to remove or significantly reduce any antinutritional elements in the food grain legumes. Table 11 summarizes the various processes that have been studied and their effect on nutritive value. The most common way by which food legumes are processed is by subjecting them to a thermal process. Although the main reason for thermal processing is to render the grain soft, its effects go beyond the changes in physical structure and texture (Bressani et al., 1984; Bressani, 1985, 1989, 1993; Bressani and Sosa, 1990). Other process methods include cooking beans at atmospheric pressure or pressure-cooking. Cooking may be done on beans with or without previous soaking in water, which typically reduces cooking time. Often in rural homes, boiling is repeated three or four times per day until the amounts prepared are all consumed (Bressani, 1993a). This practice is significant from the point of view of gastronomic acceptability and nutritive value. Cooking beans in water, with or without pressure, increases the protein quality and the protein and carbohydrate digestibility, and it inactivates protease and amylase inhibitors, as well as lectins (Bressani, 1993a). This process also reduces the concentration of other antinutritional factors such as tannins and phytic acid (Bressani, 1989,1993; El-Tahbey Shehata, 1992; Iyer et al., 1980). Elimination and redistribution of tannin in the cooked bean and cooking water is of interest since it may contribute to an increased nutritive value. On the other hand, cooking increases dietary fiber content from around 19 to 26%, trapping protein and probably making it unavailable. Cooking induces losses of vitamins (25-30%) and minerals (10-15%) (Augustin et al., 1981; Bressani et al., 1988; Bressani, 1993a). Cooking beans by extrusion yields food products that are often equal and sometimes superior in quality to food produced by wet cooking. In the extrusion process the bean particle size, the level of water in beans, the temperature, and the feed rate and velocity of extrusion are important factors to consider in developing products of high nutritive value. On the other 180


hand roasting beans, which enhances their flavor, also reduces their nutritive value by lowering the levels of available lysine (Bressani, 1993a). Germination and fermentation of grain legumes—uncommon practices in Latin America—increase vitamin content and reduce flatulence factors and phytic acid. Dehulling followed by cooking increases protein quality and digestibility (Bressani et al., 1982,1984; Bressani et al., 1988; Bressani, 1993a). This effect is due to the removal of not only crude fiber but also of tannins, both of which are present in the hulls of the bean. There are other methods used to process food grain legumes such as those applied to ‘tarwi’ (Lupinus) in Peru and Bolivia, which include long soaking times often in running water to remove the alkaloids present. Heat processing, when done under controlled time and temperature, usually improves the protein quality of food grain legumes (Bressani, 1985). Table 12 shows the effect of dehulling, in terms of cooking time at atmospheric pressure, on the protein quality of beans (Bressani et al., 1984). Increased cooking time reduced protein quality in both the whole and dehulled beans, probably due to loss of available lysine. Dehulling improved protein quality and digestibility, most likely due to the removal of the seed coat tannins (Bressani et al., 1984), which may contribute to decreased Table 12. Effect of cooking and dehulling on the protein efficiency ratio (PER) and protein digestibility (PD) of P. vulgaris. Cooking time min

PER

10 20 30 40 50 Casein

0.91 0.66 0.51 0.43 0.46 2.60

Whole bean PD (%) 60.8 61.6 59.9 60.3 57.7 91.2

Dehulled bean PER D (%) 1.60 1.35 1.45 1.15 1.20

70.8 73.1 71.6 73.1 69.7

Source: Bressani, 1984.

181


Table 13. Effect of processing on stability of antinutritional factors in grain legumes.

P. vulgaris 1 Raw black bean P. vulgaris Cooked + liquor Cooked P. vulgaris 2 Raw dry bean Soaking, 18 hrs 22°C Soaking + cooking (15 min) Cooking (90 min), conventional Mucuna 3 Tannin g kg-1 Raw 2.5 (100%) Dry heat 1.8 (28%) Autoclaved 0.7 (72%)

Tannic acid g 100 g-1 0.074 (100%) 0.032 (56.8%) 0.025 (66.2%) Phytic acid mg g-1 4.6 - 5.8 (100%) 30.4 - 48.3 % of raw 68.7 - 86.9 % of raw 23.4 - 43.2 % of r aw Phytic acid g kg-1 7.7 (100%) 4.9 (36%) 4.1 (47%)

L-Dopa g kg-1 78.1 (100%) 43.0 (45%) 58.6 (25%)

1 Bressani et al., 1991 (Hagerman-Butler method) 2 Iyer et al., 1980 3 Siddhuraju et al., 1996.

protein digestibility. Table 13 shows the effect of different processing methods on the reduction of antinutritional factors in grain legumes. By cooking, P. vulgaris tannic acid is reduced up to 66.2%; even though there seems to be a redistribution of tannins from cooked beans to cooking liquid (Bressani et al., 1991). Cooking beans, particularly after soaking them, will also reduce phytic acid in P. vulgaris (Iyer et al., 1980). The same is true for Mucuna. Tannins, phytic acid and L-Dopa levels are all reduced by processing (Siddhuraju et al., 1996). It is expected that other antinutritional factors are reduced as well, but additional studies are required to demonstrate that. We must not overlook the effect that processing has on the gastronomic acceptability and the nutritional value of food legumes, since the conditions used for any particular process can affect the results. Although the overall effects are well known, optimum processing conditions are not well established and the mechanisms giving the results measured still need to be understood, particularly with substances like tannins and dietary fiber. 182


4. Possible Research Program for Mucuna As Food The data so far presented indicate that: •

•

•

•

•

•

Mucuna beans are similar to common beans and other edible grain legumes in proximate composition, amino acid content and micronutrients. Mucuna beans are also similar to common beans and other edible grain legumes in content of antiphysiological substances (e.g., enzyme inhibitors, lectins, phenolic acid, tannin compounds, phytic acid, sugars), with the exception of L-Dopa, which is also present in Faba beans but at a lower content. The protein quality, the deficiencies of certain amino acids, and digestibility of protein are similar in Mucuna beans as compared to other edible grain legumes. Additional studies should be conducted on interactions between inhibitors and nutrient content, particularly with sulfur amino acids. As for other edible grain legumes, appropriate processing methods improve Mucuna’s nutritive value and significantly reduce levels of antiphysiological substances. Processing also reduces L-Dopa, though to a variable degree. Only a few studies have been conducted on Mucuna, so additional research is needed. Acceptability characteristics –including cooking properties, flavor and diet supplementary effect– merit further attention regarding Mucuna beans.

On the basis of the review conducted, the final section of this presentation will suggest important areas for future research (Table 14), the identification of which has benefited from our previous research on Canavalia ensiformis, another green manure crop: 183


Table 14. Research possibilities. 1. 2.

•

•

184

Evaluation of the immature seed - chemically, toxicologically, nutritionally, processing Dry seed a. effect of moist cooking • atmospheric vs pressure cooking • ± previous soaking • acid, neutral, alkaline pH • extrusion cooking b. other processing methods • dry heat (roasting) • germination • fermentation • frying c. agroindustrial use • isolation of L-Dopa • protein/starch

Evaluation of the immature seed: While conducting utilization research on Canavalia, it was noticed that people harvested and cooked immature seeds for consumption. Some studies were carried out with seeds at different stages of development: immature, intermediate, and mature dried seed. In the mature seed, crude fiber and protein quality were higher. However, in the immature seed nitrogen content was higher, an efficient complement to the maize protein. When dried, the pods of the immature seed had an attractive chemical composition suitable for ruminant animals. Studies on processing: The number of studies on the chemical composition of Mucuna beans is relatively large. However, studies on processing and its effect on nutritive value and antinutritional factors are very few. Therefore, they should be expanded as suggested in Table 14. The effects of atmospheric and pressure-cooking with and without previous soaking should be explored, and the results should be evaluated chemi-


•

cally and biologically using experimental animals. There are a few studies that show a beneficial effect of cooking grain legumes in an alkaline medium (Bressani and Sosa, 1990). An example is shown in Table 15 for Canavalia. The addition of lime at a level of 0.45% did induce a growth performance similar to that observed with extrusion cooking. Alkaline cooking may increase the inactivation of L-Dopa in Mucuna beans. Other processing methods that may give nutritionally acceptable products include dry heat (roasting), extrusion cooking, germination and fermentation. Like wet cooking, these processes also destroy antinutritional factors. Another possibility for how better to use Mucuna is to develop methods that help to extract and recover L-Dopa while utilizing the residue to isolate or extract the starch and protein fraction of the seed (about 50%). A method such as this was applied to Canavalia beans to obtain a protein concentrate and starch with acceptable yields (Molina and Bressani, 1973). Some studies show that Mucuna protein is made up mainly of albumin and globulins, which typically have a very attractive pattern of essential amino acids. Mucuna protein could, therefore, be developed into such useful ingredients if L-Dopa and other antinutritional factors were eliminated.

Table 15. Comparative study on the effects of four processing methods on the protein efficiency ratio (PER) of Canavalia seeds. Process Roasting (175°C, 15 min) Alkaline cooking (0.45% ) Ca(OH) 2 Cooking (15 lb pressure, 30 min) Extrusion cooking (320°C) Casein

Wt. gain (g)

Intake (g)

24 ± 5 c 46 ± 9 bc 32 ± 4 b 45 ± 6 b 133 ± 20 a

205 ± 22 c 270 ± 43 bc 228 ± 14 b 264 ± 28 b 418 ± 42 b

PER 1.12 ± 0.20 d 1.61 ± 0.11 ed 1.36 ± 0.12 bc 1.66 ± 0.16 b 2.81 ± 0.23 a

Averages with different letters are statistically significant. Soruce: Bressani and Sosa, 1990.

185


5. Bibliography Augustin, J., C.B. Beck, G. Kalbfleish, L.C. Kagal, and R.H. Mattews. 1981. Variation in the vitamin and mineral content of raw and cooked commercial Phaseolus vulgaris classes. Journal of Food Sciences 46: 1701-1706. Aw, T.L. and B.G. Swanson. 1985. Influence of tannins on Phaseolus vulgaris protein digestibility and quality. Journal of Food Sciences 50: 67-71. Braham, J.E. and R. Bressani. 1985. Effect of bean broth on the nutritive value and digestibility of beans. J. Sci. Food Agr. 36: 1028-1034. Bressani, R., L.G. Elías, and M.R. Molina. 1977. Estudios sobre la digestibilidad de la proteína de varias especies de leguminosas. Archivo Latinoamericano de Nutrición. 27: 215-231. Bressani, R., L.G. Elías, and J.E. Braham. 1982. Reduction of digestibility of legumeproteins by tannins. Journal of Plant Foods. 4: 43-55. Bressani, R., L.G. Elías, and J.E. Braham. 1984. Efecto del descascarado sobre el valor proteínico y complementario del frijol común. INCAP, Informe Anual p. 62-63. Bressani, R. 1985. Nutritive value of cowpea. In Cowpea research, production and utilization. Ed by: S. R. Singh and K.O. Rachie. Wiley and Sons. Bressani, R., E. Hernández, and J.E. Braham. 1988. Relationship between content and intake of bean polyphenols and protein digestibility in humans. Plant Food and Human Nutrition. 38: 5-21. Bressani, R. 1989. Revisión sobre la calidad del grano de frijol. Archivo Latinoamericano de Nutrición. 39: 419-442. Bressani, R. and J.L. Sosa. 1990. Effect of processing on the nutritive value of canavalia Jackbean (Canavalia ensiformis, L.) Plant Food and Human Nutrition. 40: 207-214. Bressani, R., D.R. de Mora, R. Flores, and R. Gómez-Brenes. 1991. Evaluación de dos métodos para establecer el contenido de polifenoles en frijol crudo y cocido y efecto que estos provocan en la digestibilidad de la proteína. Arch. Latino Amer. Nutr. 41: 564-583. Bressani, R. 1993a. Grain quality of common beans. Food Reviews International. 9: 217-297. Bressani, R. 1993b. Papel de los granos de leguminosas comestible tropicales en los alimentos y nutricion. In: Canavalia ensiformis (L) DC. Producción, procesamiento y utilización en alimentación animal. Primer Seminario Taller sobre Canavalia ensiformis. Maracay, Venezuela, 25-28 Junio, 1991. p. 212-41. Dako, D.Y. and D.C. Hill. 1977. Chemical and biological evaluation of Mucuna pruriens (utilis) beans. Nutr. Rept. Intl. 15: 239-244.

186


Daxenbichler, M.E., C.H. VanEtten, F.R. Earle, and W.H. Tallent. 1972. L-DOPA recovery from Mucuna seed. Journal of Agr. and Food Chemistry. 20(5): 1046-1048. Elías, L.G., D.G. Fernández and R. Bressani. 1979. Possible effects of seed coat polyphenols on the nutritional quality of bean protein. Journal of Food Science 44: 524-527. El Tabey Shehata, A.M. 1992. Hard-to-cook phenomenon in legumes. Food Reviews International 8: 191-221. Fernández, R., L.G. Elías, and R. Bressani. 1981. Variabilidad genética y ambiental en inhibidores de tripsina y hemaglutininas observados en cultivos de frijol común (P. vulgaris) provenientes de Centroamérica y Colombia. Turrialba 31: 153-161. Fernández, R., L.G. Elías, J.E. Braham, and R. Bressani. 1982. Trypsin inhibitors and hemagglutinins in beans (Phaseolus vulgaris) and their relationship with the content of tannins and associated polyphenols. Journal Agricultural Food Chemistry 30: 734-739. Hincks, M.J. and D.W. Stanley. 1986. Multiple mechanisms of bean hardening. Journal of Food Technology 21: 731-750. Iyer, V., D.K. Salunkhe, S.K. Sathe, and L.B. Rockland. 1980. Quick-cooking beans (Phaseolus vulgaris L.). II. Phytate, oligosaccharides and anti enzymes. Plant Food Human Nutr. 30: 4552. Jaffe, W. 1950. El valor biológico comparativo de algunas leguminosas de importancia en la alimentación venezolana. Archivo Venezolano de Nutrición 1: 107-111. Jaffe, W.G. 1973. Toxic factors in beans. Their functional importance. In: Nutritional aspects of common beans and other legume seeds as animal and human foods. Ed by W.G. Jaffé and J.E. Dutra de Oliveira. Archivo Venezolano de Nutrición. p 199-209. Kay, D.E. 1979. Food Legumes. Crop and Product Digest No. 3. Tropical Products Institute, London, UK. 435 p. Laurena, A., F.M. Rodríguez, N.G. Sabino, A.F. Zamora, and E.M.T. Mendoza. 1991. Amino acid composition, relative nutritive value and in vitro protein digestibility of several Philippine indigenous legumes. Plant Food and Human Nutrition. 41: 59-68. Leeds, A.R. 1982. Legumes and gastrointestinal function in relation to diets for diabetics. Journal of Plant Foods 4: 23-27. Liener, I.E. and M.L. Kakade. 1980. Toxic compounds of plant foodstuffs. Academic Press, New York. Liener, I.E. 1989. Antinutritional factors. In: Legumes. Chemistry, technology, and human nutrition. Ed by R.M. Matthews. Marcel Dekker, Inc. Mary Josephine, R. and K. Janardhanan. 1992. Studies on chemical composition and antinutritional

187


factors in three germplasm seed materials of the tribal pulse Mucuna pruriens (L) DC. Food Chemistry. 43: 13-18. Molina, M.R. and R. Bressani. 1973. Protein-starch extraction and nutritive value of the jackbean and jackbean protein isolate. In: Nutritional aspects of common bean and other legume seeds as animal and human foods. Ed by W.G. Jaffé and J. D. de Oliveira. Archives of Latino American. Nutrition. p 153-163. Ologhobo, A.D. and B.L. Fetuga. 1983. Investigations on the trypsin inhibitors hemagglutinin, phytic acid and tannic acid contents of cowpea Vigna unguiculata. Food Chemistry. 12: 249254. Rajaram, N. and K. Janardhanan. 1991. The biochemical composition and nutritional potential of the tribal pulse, Mucuna gigantea (Willd) DC. Plant Food and Human Nutrition 41: 45-51. Ravindran, V. and G. Ravindran. 1988. Nutritional and antinutritional characteristics of Mucuna (Mucuna utilis) bean seeds. Journal for Science of Food and Agriculture 46: 71-74. Siddhuraju, P., K. Vijayakumari, and K. Janardhanan. 1996. Chemical composition and protein quality of the little-known legume, velvet bean (Mucuna pruriens (L) DC. Journal of Agr. and Food Chemistry 44: 2636-2641. Vijayakumari, K., P. Siddhuraju and K. Janardhanana. 1996. Effect of soaking, cooking and autoclaving on phytic acid and oligossacharide contents of the tribal pulse, Mucuna monosperma. Food Chemistry 55: 173-177. Walker, A.F. 1982. Physiological effects of legumes in the human diet: A review. Journal of Plant Food 4: 5-14. WHO/FAO. 1973. Energy and protein requirements. Report of Joint FAO/WHO Adhoc Expert Committee. Rome.

188