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From the charter of the United Nations university
Report of a working group sponsored by the International Union of Nutritional Sciences and the United Nations University World Hunger Programme
Edited by Peter L. Pellett and Vernon R. Young
Peter L. Pellett is a member of the Department of Food Science and Nutrition, Chenoweth Laboratory, University of Massachusetts, Amberst, Massachusetts, USA.
Vernon R. Young is a member of the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
From the charter of the United Nations University
Article I Purposes and structure
ARTICLE 11 Academic freedom and autonomy
In 1962 an international Working Group on the Evaluation of Protein Quality met in Washington, D.C., under the auspices of the Committee on International Nutrition Programs of the Food and Nutrition Board, with Dr. Nevin S. Scrimshaw as Chairman. The work of this meeting and subsequent extensive correspondence and discussions resulted in the National Academy of Sciences - National Research Council publication Evaluation of Protein Qua/ity (NAS-NRC Publ. 1100), for which Dr. Peter L. Pellett served as editor. With the rapid advance in methodologies for the evaluation of protein quality, this publication became increasingly in need of revision. For this purpose, a task force of Committee 7, "Biological and Clinical Evaluation of Protein Foods," of Commission I of the International Union of Nutritional Sciences (IUNS), under the chairmanship of Dr. Vernon Young, and the Protein-Calorie Advisory Group (PAG) of the United Nations system joined in sponsoring a meeting in Cambridge, Massachusetts, USA, held 4-6 March 1974. Members of the group were Drs. A.W. Bender, R. Bressani, K.J. Carpenter,* D. M. Hegsted, J.M. McLaughlan, M. Milner, H. N. Munro, P.L. Pellett, B.S. Narasinga Rao,* N.S. Scrimshaw, and V.R. Young.
Unfortunately, publication arrangements were so delayed that this version became outdated by the rapid progress in the field. For this reason, a working group from the current IUNS Committee 7 of Commission I, with Dr. Ricardo Bressani as Chairman, met under the auspices of the United Nations University (UNU) World Hunger Programme in Cambridge, Massachusetts, USA, 5-7 September 1979. Members were Drs. Bjorn Eggum, J.M. McLaughlan, Hamish Munro, Peter Pellett, William Rand, Kenneth Samonds, Lowell Satterlee, Nevin Scrimshaw, and Vernon Young (see the list at the end of the book for affiliations and addresses). Using the previous document as a basis, considerable revision and updating were undertaken, together with the decision that the new document should include working information of various procedures so that it might have value on a worldwide basis. Although individual papers on specific topics were submitted to the group, so many modifications, additions, and changes in emphasis were made by the working group that the group as a whole assumed responsibility for the views and opinions expressed.
The revised version developed at this meeting was once again widely circulated, and the resulting suggestions taken into account. Individuals receiving copies for their comments and criticisms included Drs. M. ArayaLopez, Santiago, Chile; A. Bender, London, UK; C.E. Bodwell, United States Department of Agriculture (USDA), Beltsville, Maryland, USA; S. Fomon, lowa City, lowa, USA; D. Calloway, Berkeley, California, USA; K. Carpenter, Berkeley, California, USA; A. Harper, Madison, Wisconsin, USA; D.M. Hegsted, USDA, Washington, D.C., USA; D. Hopkins, St. Louis, Missouri, USA; G.R. Jansen, Fort Collins, Colorado, USA; F.M. Lajolo, Sao Paulo, Brazii; J. Mauron, La Tour-de-Peilz, Switzerland; D.S. Miller, London, UK; P.R. Payne, London, UK; H. Rafalski, Lodz, Poland; Z. Sabry, FAO, Rome, Italy; D. Southgate, Norwich, UK; and B. Torun, Guatemala City, Guatemala.
Especially detailed and helpful comments and criticisms were received from C.E. Bodwell, D. Calloway, G.R. Jansen, J. Mauron, P.R. Payne, and B. Torun. To the fullest extent possible, all revisions, additions, comments, and criticisms were taken into account in this final version, which has been edited by P.L. Pellett and V.R. Young.
This report is intended to provide a broad overview of the problems and procedures applicable to protein quality evaluation. It offers a series of practical recommendations on the methods considered appropriate for the assessment of dietary protein quality for various purposes. Consideration is also given to the sequence of plant-breeding programmes to improve nutritional value. To the extent possible, it provides the necessary details for each method proposed. A glossary is included in an attempt to define and standardize the meaning of terms and ratios as they are used in this publication on protein quality evaluation. A.Y. Pellett prepared the index and performed the final library checking of the reference list.
The United Nations University was established to apply the instruments of scholarship, research, advanced training, and the dissemination of information to the solution of pressing global problems. The combat against world hunger is the focus of the World Hunger Programme, one of three initial programmes; the other two are the Programme on the Use and Management of Natural Resources, and Human and Social Development Programme. Within the World Hunger Programme, the three sub-programmes are "Food and Nutrition Policy," "Post-Harvest Conservation of Food," and "Nutritional Requirements under the Conditions Prevailing in Developing Countries." The World Hunger Programme supported both the meeting of the September 1979 working group and the subsequent editorial process for this publication.
Nevin S. Scrimshaw, Senior Adviser
World Hunger Programme, The United Nations University
Since the publication of Eva/uation of Protein Qua/ity in 1963 (1) there has been considerable work in the area of protein quality evaluation, not only with respect to defining nutritional requirements but also in relation to the practical needs to monitor and regulate protein quality in food production, processing, and marketing. In this regard, some government regulatory agencies have introduced protein quality criteria into their food standards in order to assure minimal protein values of processed foods and to provide standards of quality for commercial food products.
A new priority, which emphasizes the importance of protein quality and its evaluation, is the growing imbalance between world food supplies and population growth. When chronic food shortages are commonplace, clearly, there will be a need to utilize available food resources as efficiently as possible. At this time, it seems quite likely that developing countries, whose population expansion is putting increasing pressure on their food supplies, will have little opportunity to improve dietary protein quality through increased animal protein production. They will need to emphasize improvements of the protein content and quality in the basic plant foods, particularly cereals, food legumes, and root crops. Thus, considerations of protein quality are of importance in national and international food and nutrition policies.
Interest in protein quality has arisen also in the field of agricultural research (2, 3). This is particularly true in relation to considerations of improved nutritional value, particularly protein content and quality, in the breeding of food crops. Nearly all of the current efforts to produce improved varieties of cereals (rice, wheat, corn, and sorghum), legumes (common beans, cow peas, grams, pigeon peas, soy beans, and similar edible species), and root crops (potatoes and cassava) include evaluations of protein quality. Thus, the plant breeder has identified the need to screen for protein quality and quantity in large numbers of cultivars.
During the past decade, considerable research has been devoted to the approaches and methods used in assessing the nutritive value of food and feed protein sources.
Limitations of the methods that were in common use at the time of the previous publication are now recognized. In particular, the standardized biological assay procedures such as protein efficiency ratio (PER) and biological value (BV) are not now considered by many workers to provide satisfactory predictions of the capacity of proteins to fulfil nutritional needs. Re-evaluation of the methodology for assessing protein quality is therefore required, and in this revision modern developments are taken into full account in arriving at the recommendations for evaluation of protein quality.
The nutritional value of a dietary protein depends largely upon the pattern and concentration of essential amino acids that it provides for the synthesis of nitrogen-containing compounds within the body. This concept provides the fundamental basis for all methods that attempt to assess the protein nutritive value of a food. Thus, the quality of a protein may vary with the amount and pattern of amino acids required for the functions measured.
The comprehensive evaluation of protein quality begins with the determination of nitrogen content, identification of the principal nitrogenous constituents of the food, and assessment of nutritional values, including digestibility, by means of in vitro and in vivo assays. The final stage is determination of the capacity of the protein to meet nutritional requirements of human beings of various ages. The various chapters in part I of this report consider each phase in the evaluation of protein quality. The methods and procedures, as well as their significance and limitations in assessing the nutritional value of dietary protein sources, are discussed. Initially, a brief review is made of humans' protein and amino acid requirements as a basis for subsequent considerations of protein quality. Then the chemical, microbiological, and enzymic methods for the determination of protein and amino acids, and methods that are less direct but potentially useful in screening large numbers of samples for these constituents, are discussed. A chapter is devoted to the assessment of protein quality from amino-acid profile and digestibility data. This approach provides a relatively easy means of obtaining an approximation of the nutritive value of a protein or a mixture of proteins, and may be the only means of judging the potential of a protein source. Although chemical and in vitro methods provide initial information on the possible nutritive value of a protein, it is desirable and often essential to explore the nutritive value of proteins in vivo. Since food protein sources for direct human feeding require experimental evaluation of protein quality and, furthermore, the introduction of unconventional protein foods and changes in the usual dietary sources of protein intake make it important to assess the nutritional impact of protein quality in reference to humans, the biological assay of protein quality in both experimental animals and human subjects is discussed. A separate chapter covers the evaluation and choice of specific assay procedures.
Part 11, on the other hand, provides detailed methodology for workers concerned with various aspects of protein quality evaluation. The methods discussed range from relatively simple chemical procedures to suggested protocols for human studies. Inclusion of procedures in this report does not imply specific endorsement but is an attempt to make a wide range of relevant procedures available to investigators throughout the world whose facilities and requirements may vary greatly. The final chapter in part 11 outlines some of the statistical techniques for handling the data generated in such protein quality evaluation procedures.
Part 111 is a glossary of terms used in protein quality evaluation, in an attempt to define and standardize the meaning of terms and ratios as they are used not only in this publication but also on a worldwide basis.
Because there is a need to develop newer and improved crop varieties, consideration should be given to the sequence and methods of procedures to be followed in the monitoring and development of plant breeding programmes. A summary of the recommendations of the Protein-Calorie Advisory Group (PAG) of the United Nations system (4) is given in appendix A. Appendix B, in two parts, lists a selection of reviews and texts in the field of protein evaluation, and relevant documents from the PAG and from the United Nations University World Hunger Programme.
This report is not an exhaustive review of the problems and procedures applicable to a protein quality evaluation. Rather, it is intended to provide a broad overview and assessment of strengths and weaknesses of the various methods that may be used in the evaluation of dietary protein quality. However, an effort has been made to include the detailed descriptions of a number of established and new methods so that they may be applied by workers who may not have ready access to the original literature.
1. Committee on Protein Malnutrition, Food and Nutrition Board, National Research Council, Evaluation of Protein Quality, ed. P.L. Pellett, NAS-NRC Publ. 1100 (National Academy of Sciences, Washington, D.C., 1963). 2. J.H. Hulse, K.O. Rachie, and L.W. Billingsley, eds., Nutritional Standards and Methods of Evaluation for Food Legume Breeders, IDRC-TS7e (International Development Research Centre, Ottawa, Canada, 1977). Nutritional Eva/uation of Cereal Mutants, proceedings of an Advisory Group meeting, Vienna, July 1976, ST1/Pub. 444 (International Atomic Energy Agency, Vienna, Austria, 1977) 4. "Protein Methods for Cereal Breeders as Related to Human Nutritional Requirements," PAG Guideline No. 16,PAG Bulletin, V (2): 2248(1975).