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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderNutritional evaluation in humans
View the document(introduction...)
View the documentIntroduction
View the documentEvaluation of products of bioconversion for human consumption
View the documentProcedures for nutritional evaluation in humans
View the documentThe evaluation of various food products
View the documentConcept of productivity
View the documentConclusions
View the documentReferences
View the documentDiscussion summary: Papers by van Weerden, Shacklady, and Bressani

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.