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The need for food utilization and processing studies to supplement nutritional evaluation

R.A. Luse

International Centre of Tropical Agriculture (CIAT), Cali, Colombia

Statements of Interest at the International Centres on Product Quality

The two international agricultural research centres at which the author has worked have made very positive statements regarding their intent to improve the quality of the commodities with which they are concerned. The term "quality" has been interpreted to include both nutritional value and consumer acceptance factors. The International Centre of Tropical Agriculture (CIAT) in Call, Colombia, has stated its objectives as follows: "To generate and deliver, in collaboration with national institutions, improved technology which will contribute to increased production, productivity and quality of specific basic food commodities in the tropics-principally in countries of Latin America and the Caribbean-thereby enabling producers and consumers, especially those with limited resources, to increase their purchasing power and improve their nutrition."

The International Institute of Tropical Agriculture (IITA) in Ibadan, Nigeria, has given the following as one of its major objectives: "To increase yields and improve the quality of food crops in the humid and sub-humid tropics through every available means, especially the development of high-yielding and insect- and disease-resistant plants."

These statements have been taken as a clear mandate to examine several aspects of quality in the food crop varieties being developed at these centres, especially cowpea ( Vigna unguiculata), lima bean (Phaseolus lunatus), and cassava (Manihot escutenta) at IITA, and the field bean (Phaseolus vulgaris) and cassava at CIAT.

Present Activities of IITA and CIAT on Product Quality

International Institute of Tropical Agriculture (IITA)

A programme to evaluate nutritional content and consumer acceptance of new grain legume cultivate was established and was closely integrated with the plant breeding activities in 1973. Evaluation extended from initial mass screening for seed protein content and protein quality, through determination of complete amino acid composition of selected lines, to measurement of consumer acceptance factors. As promising lines were identified in any of the other legume screening programmes (e.g., pathology, entomology), these lines were evaluated for nutritional content and consumer acceptance. Of the more than 8,000 lines in the IITA world collection of cowpea germ plasm, more than 5,000 were screened for protein content and protein quality. This first-stage screening relied on determination of total nitrogen content to estimate seed protein and of total sulfur content to estimate the sulfur-containing amino acids that limit protein quality. The result of this work was to identify four classes of cowpeas on the basis of their content and quality of protein for use in subsequent plant breeding work. Two classes were of particular interest: The first consisted of lines having high sulfur and high nitrogen content, found with a frequency of about 0.1 per cent. The second contained lines, occurring with a frequency of about 0.06 per cent, that had higher than average protein quality, as indicated by their high sulfur to nitrogen ratios (S/N). The latter class is the likely source of genes for high-protein quality and was used in subsequent plant breeding work. To confirm this initial screening, the amino acid composition of these cowpea lines was determined by ion exchange chromatography.

In order to estimate the acceptance of new IITA cowpea cultivars by consumers in West Africa, several factors that determine acceptance were measured. These include cooking time and water uptake for whole beans, and the taste, texture, and appearance of dishes prepared from ground beans. Cooking time and water uptake (or the ability to "fill the cooking pot") were measured by plotting increase of wet seed weight as a function of the time that beans were submerged in boiling water. The beans initially absorbed water linearly with time, but at the point where they were judged cooked by test panel members, water uptake stopped. Cooking time was thus taken as the time to reach this plateau, while swelling was directly related to the maximum water absorption. More than 100 cowpea lines were screened for these two factors. Cooking times ranged from 35 to 90 minutes and water uptake from 98 - 170 per cent. Only those lines with short cooking time and high swelling capacity were acceptable to consumers.

Cowpeas are frequently consumed in West Africa as fried akara balls and steamed moin-moin, both of which are prepared from ground beans. In order to estimate this aspect of consumer acceptance, these dishes were made from local recipes, using flour of IITA cowpea cultivars. This work was done in cooperation with the test kitchen of the University of Ibadan. Taste panels graded the product on the basis of taste, texture, and appearance. A high-quality cultivar was always included in the test as a standard, so that results were stated as preference or non-preference of the IITA cultivar compared with the standard.

A limited number of informal dietary surveys were carried out by IITA staff as a part of our nutritional studies. A number of more formal surveys done by the Food Science and Applied Nutrition Unit of the University of Ibadan were made available to us as unpublished reports. On the basis of these reports and others, it was determined that grain legumes are an important source of protein in the diets of people living in villages in Southern Nigeria, but that green leafy vegetables and other components of the soups and stews eaten daily also contribute more protein than is usually realized.

In work done by the IITA plant physiologist, a large number of cassava plants were tested for cyanide level because this is an important factor in nutritional value for the so-called "bitter" varieties having high levels of cyanogenic glucoside. Nearly 100,000 plants were screened during the period of this work, using a very simple colour test with sodium picrate paper. Frequency of plants having low cyanide content was judged to be about 3 per cent, though in certain composites developed in the breeding programme, the frequency of low cyanide cultivars reached over 7 per cent. In other work, done by the IITA starch chemist, the theological properties of cassava starch were studied, together with their relation to consumer preference factors such as texture and gari manufacture.

International Centre of Tropical Agriculture (CIAT)

Work on cassava quality at CIAT centers primarily on post-harvest storage and processing. Cassava is a highly perishable crop, with physiological deterioration of the roots often beginning within two days after harvest and microbial deterioration starting in less than one week. The fresh roots are bulky to handle, as they have a water content of about 65 per cent. Simple methods are needed to solve these problems of perishability and the bulky nature of the root. Recent work at CIAT has shown that high-quality stored roots may be achieved by either pre-harvest leaf pruning or by packing the roots subsequent to harvest in polyethylene bags containing a fungicide. The problem of residual fungicide toxicity may not be serious, because cassava is peeled before eating, but it is essential to search for less toxic materials and to determine any residues remaining in the roots. A number of research centres in the world are studying simple methods utilizing solar energy for the drying of cassava. CIAT scientists will be testing these methods and, if necessary, adapting them to fit the needs of the Latin American cassava producer.

At the present time the author is setting up a programme at CIAT to screen all advanced Phaseolus bean lines coming from the breeding programme for protein content. Cooking time in these lines will also be studied, although with emphasis primarily on ways to reduce cooking time through simple chemical treatment during soaking or through proper storage conditions. Here it may be noted that the treatment of seeds with edible oil, a method found effective against weevil attack on cowpeas and field beans, is being examined for its possible reduction of hard seed coat development during poor storage conditions. As other methods are proved of value in determining nutritional value and for estimating consumer acceptance, they will be applied at CIAT in a full screening programme for bean quality.

Proposed Activities for Quality Evaluation and Utilization

Nutritional evaluation

Estimating the nutritional value of a foodstuff requires knowledge of three important factors: its role in actual dietary consumption, its protein digestibility, and how it is processed for food. While it is necessary to have a general idea of the amino acid composition of a foodstuff, there is a complementary balancing of amino acids between cereals and legumes (lysine from legume methionine from cereal), so that simple amino-acid scores are of limited value in estimating the true value of mixed diets. This point has been well made by Bressani in the case of maize and dried beans in Central America. An even more impressive case can be made for cowpea-sesame seed mixtures (see Table 1), where the complementarity is excellent and serves as the basis for the "benniseed" "benniseed" weaning food in Sierra Leone.. A less exact matching is that of pigeon pea and millet (Table 2), though here the chemical score may be nearly doubled over those of the components through an appropriate mixing. The factor of protein digestibility becomes important when food legumes are involved, because they typically have digestibilities of only 69 - 83 per cent. Lastly, processing of the foodstuff may have important effects on its nutritional value and digestibility, and can convert a poor foodstuff into a good food.

TABLE 1. Amino Acid Patterns in Cowpea and Sesame Seed and Their Mixture

Amino acid Amino acid content,
mg/g N
Isoleucine 290 250 270 250
Leucine 530 440 485 440
Lysine 490 195 340 340
+ cystine
180 310 245 220
Phenylalanine+ tyrosine 640 550 600 380
Threonine 290 250 270 250
Tryptophan 100 110 105 60
Valine 370 310 340 310
Chemical score 82 57 100  

Limiting essential amino acids: methionine + cystine, lysine

The above statements imply that when strategies for plant improvement include evaluation of nutritional characteristics, plant breeders need to have dietary consumption data for the target areas where the improved varieties will be used, plus additional information beyond the usual amino acid composition, preferably NPU or equivalent nutritional values. Obtaining such figures is outside the activities of the international centres, and there is a good case to be made for working co-operatively with national and regional institutes of nutrition and food science. To generate this information, CIAT is at present proposing such co-operation with the Institute of Nutrition of Central America and Panama (INCAP) in Guatemala and with the National Institute of Nutrition in Caracas.

Food preparation and processing studies

Included in the CIAT studies is a small amount of work on the study of food preparation techniques (typically at the household and village level), and of commercial food processing techniques (typically at a national or regional level). This is because there is a possibility to extend traditional food preparation methods so as to improve both the nutritional quality and consumer acceptance of the food actually reaching the consumer. Here such techniques as chemical treatment during soaking to produce a "quick cooking" bean may be considered. Processing at the commercial level, and possibly even at the community level, also needs to be studied, with the idea of introducing modern techniques such as low-cost food extruders. These types of studies might have a profound influence on the actual utilization of beans in Latin America.

TABLE 2. Amino Acid Pattern in Pigeon Pea and Millet Seed and Their Mixture

Amino acid Amino acid content,mg/g N FAO/WHO pattern, 1973
Pigeon pea Millet 33 - 67% mixture
Isoleucine 194   230   218 250
Leucine 394 783 655 440
Lysine 481 167 271 340
Methionine 32 93 120 217 176 220
+ cystine 61 97
Phenylalanine 517 643 305 544 577 380
+ tyrosine 126 239
Threonine 182   225   211 - 250 60
Tryptophan - -
Valine 225 303 277 310
Chemical score 42 49 80 -

Limiting essential amino acids: methionine + cystine, lysine; methionine + cystine and lysine equally.

Such studies are also generally outside of the proper scope of the international centres, yet there needs to be a dialogue between plant breeders, who know the genetic diversity within their crop, and the food technologists, who know what their equipment can do. It is hoped that the food scientist will tell the plant breeder what characteristics are required for a given processing technology so that the plant breeder can develop it. In many cases, changes in the processing steps may be necessary to utilize available genetic diversity, but it should be possible to end with a compromise between what the processor demands and what the plant breeder can produce, to the ultimate benefit of the consumer. There is also a subtle benefit for the international centres here, because, in the developing countries which are the centres' target areas, consumer preferences in such basic foodstuffs as beans are often sharply defined. Without good acceptability/preference characteristics, a new crop variety will find no market, and hence low acceptance by the farmer producer. The centres would be well advised to know these preferences, and how they may be met by processing, and to carry out their plant improvement programmes accordingly.


The multidisciplinary programme to improve the cowpea for West Africa, carried out at the International Institute of Tropical Agriculture (IITA), included both nutritional evaluation (protein, sulfur amino acids), and consumer acceptance factors (cooking time, taste, texture, and appearance of prepared cowpea dishes). Such screening identified cowpea varieties combining superior yield potential, good nutritional value, and high consumer acceptant e. A similar programme at CIAT to improve the field bean (Phaseolus vulgaris) will include screening for content of protein, methionine, lysine, tryptophan, and anti-nutritional factors, plus cooking time, seed characteristic preferences, and suitability for processed foods.

It is felt that the international agricultural research centres should extend their present nutritional screening activities and should have staff responsible for assessing consumer utilization and processing methods. In developing countries, consumer preferences in basic foodstuffs are often sharply defined. Without good acceptability/preference characteristics, a new crop variety will find no market, and thus be undesirable to the farmer producer. The international centres and national plant breeding programmes should encourage food utilization and processing research in national nutrition and food science institutes and work co-operatively with them.

Dietary Effect of Fibre on Protein Digestibility-A Correction

We regret that Table 3.2 on page 27 of the report Protein-Energy Requirements under Conditions Prevailing in Developing Countries: Current Knowledge and Research Needs, distributed as a supplement to the May 1979 issue of the Food and Nutrition Bulletin, contained an error that alters one of the conclusions

A revised table appears in later printings.

The figure for protein retention by the US student group on an egg formula fibre-free diet should have beer 91 3, not 87 3. Instead of the addition of oat fibre to the egg formula diet having little effect on its nitrogen absorption, the correct conclusion would be that it had a significant negative effect. The correct table is as follows.

Revised TABLE 3.2. Percentage Absorption of Nitrogen and Calories from Diets of Varying Fibre Content by Guatemalan and US Males Fed 0.6 9 Protein per kg Body Weight

  Guatemalan corn-
black-bean diet
Egg formula
fibre-free diet
Egg formula diet
with oat bran







24 rural lowland Guatemalan males 15 - 45 Years old 73 10 914 764 953 - -
13 rural lowland Guatemalan males after 20 - 23 months' military service 855 922 - - - -
6 US male university students*** 692 892 913 971 864 942

* Apparent protein digestibility, % dietary N-faecal N/dietary N x 100.
** Digestible energy, % = dietary keel (bomb)-faecal kcal (bomb)/dietary kcal (bomb) x 100.
*** D.H. Calloway and M.J. Kretsch, "Protein and Energy Utilization in Men Given a Rural Guatemalan Diet and Egg Formulas with and without Added Oat Bran, Amer. J. Olin. Nutr, 31: 1118 (1978).


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