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Concept of productivity

Economic considerations in systems of food production, whether they are food crops, livestock, or bioconversion products, take into account only the total amount produced, with little regard to whether the products will be used efficiently. In view of this, we define productivity as total production per hectare, or per unit of weight or volume, corrected by a food technology factor and by a nutritive value factor (18):

TABLE 4. Protein Quality of Chlorella, Yeast, and Casein in Human Subjects









True protein





B.V. %

Casein + RNA 4.25 - 1.00 95 66
  7.84 +0.33 99 52
Chlorella 4.83 +0.28 89 79
  7.81 +0.05 82 60
Torula 4.51 - 1.23 83 70
  8.20 +0.39 87 58

Source: Waslien et al. (17).

Productivity = Production/ha x Food technology factor x Nutritive value

This equation is applicable to production of foods from soil or other sources, such as those described in these proceedings, and is applicable to evaluation of feed for animals and also food for human consumption.

The term "food technology" in the formula has two components. One is related to those characteristics of a food or product that introduce functionality, texture, and structure to food systems. For example, the high-yielding variety of rice IR8 was not accepted by the consumer because it did not meet the eating quality associated with rice. The second component is related to the capacity of the product to undergo processing without physical, chemical, or microbiological deterioration. An example would be milled Opaque-2 corn, which has a low yield of grits because of the nature of the endosperm. In the area of biomass, specifically algae, the green colour is an example of the first food technology component, and bacteria-induced deterioration is an example of the second.

The nutritive value factor in the equation is related to the efficiency with which the nutrients of the food products, whether they are calories, proteins, or any other specific nutrients, are utilized.

One example that shows the effect of better land use through a more efficient utilization of the protein in cereal grains is presented in Table 6. For children, the amount of protein from corn needed for equilibrium, that is, neither weight gain nor loss, requires cultivation of 69 and 182 kg/yr of Opaque-2 and common maize, respectively. These amounts of protein are lost in faeces and urine because the figures represent the condition at protein equilibrium, and are equivalent to 0.013 and 0.035 ha per person per year. For adults, the results show the same trend; i.e., less land use due to more efficient utilization of the nutrients in Opaque-2 maize than those in common corn. Therefore, productivity expressed in production per unit area should also include the efficiency of utilization of the crop produced. Even with the 10 - 15 per cent lower yield and a slightly lower food technology factor, Opaque-2 maize has a higher productivity than can be derived from common corn.

TABLE 5. Urinary and Plasma Uric Acid Levels of Men Fed Nucleic Acid Added to Casein and as Found in Algae and Yeast

Diet Nucleic acid

intake (g/day)

Uric acid (mg)


Plasma/100 ml
Protein-free 0 394 5 4
Casein + RNA      
25 g prot 1.8 562 6.9
50 g prot 3.7 886 8.7
25 g prot 1.7 605 7.4
50 g prot 3.6 872 9.7
25 g prot 5.0 942 10.2
50 g prot 10.3 1,536 12.6

Source: Waslien et al. (17).

Table 7 shows the significance for productivity of low and high digestibility bean protein. Using the results from nitrogen balance studies, it can be seen that low digestibility results in poor land use because significant amounts of N are lost in the faeces in comparison to N loss when a material of higher digestibility is fed.

TABLE 6. Amount of Corn Protein Found Experimentally to Be Necessary for Nitrogen Equilibrium in Children and Adult Subjects

  Type of corn


g protein/child/day 16.8 45.0
g corn/child/day 188 500
kg corn/child/year 69 182
ha/person/year 0.013 0.035
g protein/head/day 27.9 43.8
g corn/head/day 250 547
kg corn/head/year 91 200
ha/person/year 0.018 0.040

The above is based on a yield of 5,000 kg/ha.

TABLE 7. Efficiency of Land Utilization in Terms of the Protein from Beans (Phaseolus vulgaris)


of 64%



of 84%


Yield of beans/ha, kg 1,000 1,000
Yield of protein/ha, kg 230 230
Protein absorbed/ha, kg 147 193
Protein waste/ha, kg 83 37
Waste as beans/ha, kg 360 160
% land poorly utilized 36 16
Nitrogen intake 227 227
Faecal nitrogen 81 36
Urinary nitrogen 109 109
Nitrogen absorbed 146 191
Nitrogen retained 37 82

Finally, energy inputs into agricultural production systems are also affected by the quality of the end-product. Table 8 shows calculation of agricultural and nutritional efficiency using data from Pimentel et al. (19).

With respect to nitrogen input, agricultural efficiency for corn is 0.61 whether it is common or Opaque-2 maize. However, the nutritional efficiency of the nitrogen input is 0.44 for Opaque-2 maize and a significantly lower value of 0.19 for common corn. For energy inputs, the returns of agricultural efficiency for both types of corn would be 2.82; on the other hand, the nutritional efficiency of the energy input would be 1.35 for Opaque2 corn and a very low value of 0.87 for common corn.

TABLE 8. Agricultural Productivity of Cereal Grains of Improved Nutritional Value Out put/input

Parameter Output/input

Common corn

Opaque-2 corn
For N inputs in corn production    
Agricultural efficiency (grain) 0.61* 0.61*
Nutritional efficiency 0.19 0.44
For energy input in corn production    
Agricultural efficiency (grain) 2.82. 2.82*
Nutritional efficiency 0.87 1.35

* Equal yields/ha were assumed.

These calculations indicate that, independent of the nutrition problem, there are practical advantages in producing food grains of the highest possible protein quality.


As I indicated in the introduction to this paper, the harvest indices from food crops are small, and the amounts of potential energy left in the field are very large. Even smaller indices are obtained after food is processed, indicating still greater wastes. As the papers in this proceedings show, there are various products that can be made by bioconversion. In my opinion, especially in rural areas, priority should be given to processes that will convert wastes into materials that will induce better structure and fertility in soils and hence make them more productive. Second, biogas production also has potential and is a system that is compatible with bioconversion processes. A third approach would be to produce biomass that, without any further processing, can be used as animal feed. Some wastes can be converted into foods for man, but because of the types of raw material used and the subsequent processing needed to make such products wholesome for human consumption, large-scale industries are required. Quality products can thus be made to enter the present food consumptions systems.


1. J.E. Braham and R. Bressani, (eds.), Pulpa de Cafe. Composición, Technologia y Utilización. IDRC 108 s.

2. Protein-Calorie Advisory Group of the United Nations System (PAG) Guideline No. 6, "Preclinical Testing of Novel Sources of Protein," United Nations, New York.

3. PAG Guideline No. 7, "Human Testing of Supplementary Food Mixtures," revised, in PAG Bulletin 3 (No. 3): 12 19 119731.

4. PAG Guideline No. 8, "Protein-Rich Mixtures for Use as Weaning Foods," United Nations, New York, 1971.

5. PAG Guideline No. 12, "Production of Single-Cell Protein for Human Consumption," United Nations, New York, 1972.

6. PAG Guideline No. 15, "Nutritional and Safety Aspects of Novel Protein Sources for Animal Feeding," United Nations, New York.

7. D.A. Navarrete, V.A. Louiro de Daqui, L.G. Elías, P.A. Lachance, and R. Bressani, "The Nutritive Value of Egg Protein as Determined by the Nitrogen Balance Index (NBI), Nutr. Rep. Internat. 16:695 704 (1977).

8. R. Bressani, D.A. Navarrete, L.G. Elias, and J.E. graham, "A Critical Summary of a Short-Term Nitrogen Balance Index to Measure Protein Quality in Adult Human Subjects," in H.L. Wilcke, D.T. Hopkins, and D.H. Waggle (eds.), Proceedings of a Conference on Soy Protein and Human Nutrition, Keystone, Colorado, 22 25 May 1978. Academic Press, New York. (proceedings in press.)

9. R. Bressani and E. Marenco, "The Enrichment of Lime-Treated Corn Flour with Proteins, Lysine and Tryptophan, and Vitamins," J. Agric. Food Chem. 11: 517 - 522 (1963).

10. R. Jarquin, P. Noriega, and R. Bressani, "Enriquecimiento de Harinas de Trigo, Blanca e Integral, con Suplementos de Origen Animal y Vegetal," Arch. Latineamer, Nutr. 16: 89 - 103 (1966).

11. L.G. Elias, R. Jarquin, R. Bressani, and C. Albertazzi, Suplementación del Arrox con Concentados Proteinicos," Arch. Latinoamer. Nutr. 18: 27 - 38 (1968).

12. G.A. De la Fuente, M. Flores, R. Molina, L. Almengor, and R. Bressani, "Some Nutritional Characteristics of a Naturally Occurring Alga (Microcystis sp.) in a Guatemalan Lake," Appl. Environ. Microbiol. 33: 6 - 9 (1977).

13. Y. Morimura and B. Tamiya, "Preliminary Experiments in the Use of Chlorella as Human Food," Food Technol. 8: 179 - 182 (1954).

14. R.C. Powell, E.M. Nevels, and M.E. McDowell, "Algae Feeding in Humans," J. Nutr. 75: 7 - 12 (1961).

15. R. Dam, S. Lee, P.C. Fry, and H. Fox, "Utilization of Algae as a Protein for Humans," J. Nutr 86: 376 - 382 (19651.

16. S.K. Lee, H.M. Fox, C. Kies, and R. Dam, "The Supplementary Value of Algae Protein in Human Diets," J. Nutr. 92: 281 - 285 (1967).

17. C.I. Waslien, D.H. Calloway, S. Margen, and F. Costa, "Uric Acid Levels in Men Fed Algae and Yeast as Protein Sources," J. Food Sci. 35: 294 - 298 (1970).

18. R. Bressani, "Productivity and Improved Nutritional Value in Basic Food Crops," in Improving the Nutrient Quality of Cereals. II. Report of Second Workshop on Breeding and Fortification, September 1976, p. 265, AID Washington, D.C.

19. D. Pimentel, L.E. Hurd, A.C. Belloti, M.J. Forster, I.N. Oka, O.D. Sholes, and R.J. Whitman, "Food Production and the Energy Crisis," Science 182: 443 - 449 (1973).

Discussion summary: Papers by van Weerden, Shacklady, and Bressani

Asked about the meaning of the term "technological quality" of proteins, Dr. 8ressani replied that the phrase was used to indicate how amenable (or otherwise) protein preparations are to normal domestic or industrial processing. It was recommended that new preparations should be evaluated in terms of their replacement for other protein sources rather than in absolute terms. This is, in fact, the normal procedure when evaluating food mixtures for human consumption.

Senez, commenting upon van Weerden's paper, pointed out that the rations containing yeast in the experiments he described were generally supplemented with methionine. With regard to the apparent differences in species response to the fungus tested, he wished to stress that it related to only one out of several thousands of fungi that might be used. van Weerden agreed with both comments, but said that the latter served to underline his contention that we know very little about this very large subject.

Stanton commented upon the one in one million level of risk mentioned by Shacklady and said this was close to the natural frequency of mutation of many bacteria. He also suggested that Tetrahymena pyriformis could be a useful organism for field-workers comparing or evaluating potential feed ingredients. In reply, Shacklady said that the one in one million possibility of error referred, not to mutagenicity studies, but to lifespan feeding studies on experimental animals, and simply indicated the magnitude of the studies acceptable to the FDA Regarding T. pyriformis, this has been used by some workers as an index of protein quality, but it has a number of disadvantages, one being that it does not have an absolute requirement for lysine, frequently the first limiting amino acid in cereals. As far as Shacklady knows, it has not been used in mutagenicity studies, the most commonly used organisms being Salmonella typhimurium mutants along with those of Escherichia cold and Bacillus subtilis.

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