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An index of quantitative and qualitative food loss

C.P.F. De Lima Crop
Storage Section, Malkerns Research Station, Malkerns, Swaziland

Introduction

On a global scale all food losses are important, but local differences require attention. Most countries have a food staple: maize in South, East, and Central Africa, roots and tubers in Europe and America. In some countries, there may even be a significant variation in diet within the country. For example, in India wheat is the staple in the north, and rice is the staple in the south. The main food is usually supplemented by significant amounts of other products. In some countries the protein requirement is met from legumes and pulses, in others from fish. Important nutrients are obtained from fruits and vegetables. All these foods are subject to varying degrees of qualitative and quantitative loss.

Aspects of food loss

From the moment of harvest until it is eaten, most food, including fish, is subject to degradation from a variety of causes. Deterioration may occur relatively slowly in cereals and pulses (durable produce) and more rapidly in fruits and vegetables (perishable produce). The rate of loss may be slowed down in a number of ways: by destroying the "agents" of loss by chemical means or reducing their effect by "curing" the product or modifying its physical environment (cold storage, inert atmospheres, etc.).

Under the conditions of tropical subsistence agriculture, preserving agents, pesticide chemicals, inert gases, and cold storage are not readily available, economically justifiable, or technologically appropriate for general use. Stored foods therefore deteriorate fairly rapidly (fig. 1). Perishables lose half their quality within 2 weeks and cannot be graded after 3 weeks; on a quantitative basis, half the product may be eaten after 21/2 weeks, and none after 4 weeks.

This general picture varies from product to product; for example, freshly harvested fish may deteriorate within hours, while a coconut may "go bad" after 8 weeks. Durable produce retains harvest quality during the first 8 weeks, loses half after 18 to 20 weeks, and is "under" grade" after 26 weeks; quantitative loss is slower, and after one year's storage, there is still half the original amount. The curves for deterioration in figure 1 refer to loss in the absence of human consumption. Quantitative estimates of loss made on a national basis would take into account human consumption, among other things, and final loss would be lower.

Qualitative and Quantitative Deterioration of Food stored

TABLE 1. Calculation of the QST Index for Stored Food in Kenya

* Ministry of Agriculture, Kenya, 1978.

These and other aspects make it difficult to obtain a clear, overall picture of food loss in a country unless a way can be found to represent on a single (self-weighing) scale the losses suffered by so many products from so many causes. A new index, the QST index, has been developed to give quantitative (weight) loss and qualitative (e.g., protein) loss comparisons for durable and perishable produce to guide resource allocation in the planning and conduct of food-loss surveys.

The QST index

The index is obtained in the following way. First, a list is made of the food that is produced and consumed in the country. Then an estimate is obtained of the amounts consumed in urban and rural areas (or other use) and the storage time for each. The quantity of the produce stored is then multiplied by the pivotal storage time and the values so obtained scaled to 100 (table 1). For example, maize in Kenya is stored for rural and urban consumption as well as in reserve for famine. The length of time and the quantities of maize stored for each use vary, and this is reflected in the value of the QST index. Thus, maize accounts for nearly 80 per cent of the index on a national basis and almost five-sixths of rural consumption of food grains.

The value of the index in identifying the relative importance of various commodities is illustrated in figure 2. Here, the annual QST index has been broken down for various commodities for the harvesting and storage periods. Thus, the proportion of the crop harvested in the long and short rainy seasons can be shown, as well as the overlap between harvesting and storage times. The calculation and plotting of the QST index on a country basis provides valuable guidance for planning of food storage programmes and facilities.

For loss assessment on a physical (weight) basis or from a nutritional standpoint, the relevant factor can be obtained by field or laboratory investigation or from published data. This factor can then be multiplied by the index and the index re-scaled to 100 to provide a new index for the characteristic under study. For variables that increase with storage time, e.g., weight loss, the pivotal estimate would be appropriate. For "constants" such as protein per cent, the actual value is justified. Therefore, the estimate of weight loss for various products in Kenya (values for perishables are based on an informed guess) can be indexed to give the QSTw for weight loss or QSTp for protein loss. These data show that about 70 per cent of the weight and protein losses occur in maize, the staple food, and about 25 per cent in perishables (table 2). Activities for loss reduction should therefore be directed at these commodities.

Discussion

As I have discussed elsewhere (1, 2), programmes to establish country losses must establish priorities and have a defined scope of work. This can be more easily achieved by use of the QST index. The value of the index in drawing quantitative and qualitative comparisons of a wide variety of commodities on a national basis is established. Similarly, the index can be used to evaluate the economic costs of pest control; weight and grade losses; drying and other storage facilities, etc., on a national basis to guide planning strategies.

Fig. 2. partitioning of the annual qst index over the Long-Rain and Short-Rain Harvest for Maize, Pulses, and Roots and Tubers in Kenya. (LH = long-rain harvest; SH = short-rain harvest)

TABLE 2. Use of the QST Index to Determine Weight and Protein Loss on a Country Basis

References

1. C.P.F. De Lima, "Appropriate Techniques for Use in the Assessment of Country Loss in Stored Produce in the Tropics," Trop. Stored Prod. Inf., 38: 16-19 (1979).

2. C.P.F. De Lima, "The Conduct of Field Infestation Surveys and the Economic Use of Their Results," in Proceedings of the First International Working Conference on Stored Product Entomology, Savannah, USA, October 7-11, 1974 (1975), pp. 47 60.

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