Contents - Previous - Next

This is the old United Nations University website. Visit the new site at http://unu.edu

Post-harvest losses: extent of the problem

Agide Gorgatti-Netto
Director General, Food Technology Institute, Secretary of Agriculture for the State of Sao Paula, Campinas, Brazil (ITAL)

In the last decade, worldwide production of basic food has increased faster than the total population has grown - about 2.5 per cent per year vs. 1.9 per cent for population increase. However, in the developing countries, despite a 3.2 per cent increase in-food production each year, production has barely kept ahead of the rate of population growth. A variety of factors underlie the world food problem, and the imbalances between developed and developing countries. One is avoidable losses of food crops. After all the effort devoted to produce food, it is of utmost importance to handle it carefully after harvest.

For this reason, priority should be given to post-harvest studies, particularly in humid tropical climates where at least half of the food supply from plants and animals may be lost between harvest and consumption. The magnitude of these losses can only be estimated, because so few assessments are available. For grain crops, the conservative estimate is that at least 10 per cent are lost after harvest in developing countries, and losses up to 40 per cent have been recorded. These losses are classified in Table 1.

A reduction of these losses by half could provide for almost 50 per cent of the food-grain import requirements of developing countries by 1985, at a value of about $US 8 billion. Losses may be either in quantity or quality, or both. Losses in quantity are more easily determined; for example, the difference in weight of grains infested with insects. However, deterioration of nutritive quality is often overlooked and is more difficult to determine.

THE DIMENSIONS AND CAUSES OF THE PROBLEM

Low agricultural yields have been blamed for world food problems, but can we continue to emphasize only agricultural production when an average of 30 per cent of the crops raised never reaches the consumer? Damage caused by insects, rodents, or birds varies extensively in different areas, particularly with respect to cereals and oilseeds. Insects and rodents are the principal causes of losses of stored cereals or legumes in tropical or subtropical countries and the speed with which many insect species multiply is influenced by the moisture content of a particular commodity.

Micro-organisms, such as bacteria or fungi, are responsible for most of the losses of perishable products such as fruits and vegetables. Fungi in particular attack cereals as well as fruits and vegetables, and contribute to both quantitative as well as qualitative loss in food value and a decrease in the monetary value of the crops. Another serious concern is that certain species of fungi produce metabolic toxins, or microtoxins, for example the aflatoxin produced by Aspergillus flavus, that renders a product dangerous for both human and animal consumption.

TABLE 1. Classification of Losses

Information on post-harvest losses is still very inconsistent and scarce, especially for fruit and vegetable crops, for which losses are much larger than those of cereal crops. A recent study done in the State of Sao Paulo, Brazil, indicated that out of 23 food products, 6 kinds of fruits and vegetables accounted for 10.6 per cent to 13.3 per cent of the total food expenses of 2,380 families interviewed. From an economic point of view, tropical fruit losses are important both for these families and for their export potential. In Sao Paulo, horticultural crop losses may vary from 4 per cent to 34 per cent, depending upon the product and the efficiency of the marketing system (Table 21. In Recife, in the northeast of Brazil, horticultural crop losses caused by deficiencies in the commercial marketing system vary from 7.6 per cent to 40 per cent. In the State of Piaui, in northern Brazil, 80 per cent of the production of cashew fruit is lost every year, mainly because the fungus Rhizopus nigricans attacks the fruit after harvest, and also because the local market does not have the capacity to absorb all of the fresh fruit available or to process it for future consumption or shipment to other markets.

Data obtained in 1973 from the Ministry of Agriculture in Brazil (Table 3) show the amount of fruits produced and the

TABLE 2. Per Cent Losses during Commercial Handling of Fruits and Vegetables in Two Major Brazilian Cities, Sao Paulo (average annual temperature 23°C) and Recife (average annual temperature 31°C) in Both Wholesale and Retail Markets, 1971

*Supermarket

TABLE 3. Amounts of Fruit Produced and Estimated Losses in Brazil, 1973

Information obtained from the Brazilian Ministry of Agriculture. estimated losses that occurred that year. Losses of potatoes and onions are also high, largely because of inadequate storage and marketing conditions. Both tubers are very susceptible to poor handling procedures; they are exposed to rodents, bacteria, etc., that cause rot. Losses as high as 30 per cent are reported for both products. For onions, the major problem is that the varieties cultivated in many regions of the country, particularly in the northeast, do poorly in this environment. They have a very low percentage of total solids after harvest, do not store well under unfavourable conditions, and spoil easily during handling and transport to the market.

A survey made by the Brazilian Financing Commission (CFP) of the Ministry of Agriculture showed that 5 - 20 per cent losses occur in cereal grains during storage in both warehouses and silos. An average loss of 6 per cent was reported for cereals bought and stored by the CFP, and the major causes were (a) excess moisture content; (b) insect infestation; (c) inadequate stacking; and (d) inadequate packaging materials. A research paper published in 1970 by the Federal University of Vicosa-Minas Gerais, states that loss in weight of corn attacked by insects and rodents during storage on the farm reached 12 per cent after a period of three to seven months. Similar losses in corn weight have been reported from Zambia, Nigeria, Ethiopia, and India. Even in developed countries such as the United States and Germany, millions of dollars are lost in the value of stored cereals after harvest, indicating the complexity of the problem.

THE ROLE OF RESEARCH INSTITUTIONS

Studies in Brazil point out that the main causes of horticultural and cereal crop losses are inadequate harvest techniques, lack of, and inadequate, storage facilities, and poor transportation, handling, and packaging practices. Obviously, more knowledge about the magnitude and true nature of the losses is required, and approprate technology to reduce them should be utilized wherever it is possible.

Although appropriate technology has been the subject of a growing volume of literature, the term is open to multiple in the context of "intermediate" or "low-cost" technologies. However, the term does not refer to a specific technology, but to a concept. Appropriate technology is the one that will contribute most to the economic and social objectives of development in a given situation.

It is crucial that research institutions become involved in doing what they can to alleviate the problem. It is necessary to determine the true nature of the problem in each case and establish precise methodology for solving it. "ITAL" is the acronym for the Food Technology Institute of the Secretary of Agriculture for the State of Sao Paulo, Brazil. In the past ten years, it has been active in conducting post-harvest research with the objective of transferring the results to farmers as well as government agencies. The following studies are in progress.

1. Storage of Maize at the Farm Level

Maize is grown in most of the states of Brazil, usually on small and medium-sized farms. It is a product that is nearly always stored on the farm for use as animal feed. It is, therefore, the cereal that suffers the highest losses during storage from insects, micro-organisms, and rodents. Without any doubt, the poor storage facilities and obsolete procedures for the storing of maize in rural areas contribute to these high losses. The adoption of bulk storage systems in metal or concrete bins would be one solution, but implies a relatively high initial investment not always within reach of the small farmer. For such cases, a low-cost storage system with no need for specialized manpower for its construction is highly desirable.

The storage of grain in underground pits is one of the oldest systems known, used since remote times in South Asia. In Malta, grain is traditionally stored in large vase-shaped underground pits lined with straw. In Israel, Donahaye and co-workers improved this system by lining the pits with polyethylene sheets. They obtained good results with rye stored for 15 months. These researchers consider rodents as the possible limiting factor for this type of storage.

Underground pits allow hermetic storage conditions. The principle is that decreasing the concentration of oxygen and increasing that of carbon dioxide via respiration of grain and of insects eventually cause the insects to become inactive, and will sometimes kill them. Experiments have demonstrated that either a reduction in oxygen or an increase in carbon dioxide will kill insects within hours or days, depending on the concentrations of oxygen and CO,, the insect species, and on factors such as temperature and moisture content in the grain. It is also known that the degree of hermetic sealing required to prevent growth of fungi is much more critical than that needed to control insects in dry grain, where light infestation can sometimes be tolerated.

An experiment was set up to see whether fumigated, de husked maize with low moisture content could be successfully stored in an underground pit lined with locally available, fairly thin polyethylene. This system was developed for use on small farms. Three tons of maize were stored in a pit 2 m x 1.4 m and 1.5 m deep in well-drained red lathosol soil. The floor was covered with Malathion-treated maize straw 15 cm thick to protect the plastic sheet from abrasion and also to provide an additional buffer against moisture. The pit was then lined with a plastic sheet 8 x 7 m and filled with maize.

Hermetic conditions were attained as follows: The edges ah of the plastic sheet along the shorter (1.40 m) sides of the pit were folded toward the inside and the edges on the 2 m sides were pulled together and folded once very close to the level of the grain. A 2 m steel bar 3/8 inch in diameter was placed at each side of the folded plastic, and the bars and plastic were fixed by clamps set 20 cm apart for the length of the bar. A layer of rice husks 20 cm thick was put on top of the bin, over which a second plastic sheet 4 x 3.5 m was placed in order to achieve better thermal insulation. The upper surface was rounded to avoid rainwater infiltration, and, because of the slope of the ground, a small U-shaped channel was constructed around the bin to catch rainwater. No live insects were detected when the pit was opened for inspection after eight months of storage. The initial 4.6 per cent of insect-damaged grains did not increase during the storage period. The moisture content remained constant and uniform throughout the storage period, and no condensation accumulated at any point of contact between the grain and the plastic sheet. The initial temperature of the maize was 27.2°C. The average final temperature, taken at five different points in the maize, was 26.9°C ( minimum observed 26.2°C, maximum 27.5°C). As there was no moisture migration, it can be assumed that there was no significant temperature variation during the storage period.

Grains, as living organisms, breathe and are subject to chemical and biological transformations that modify their composition. The intensity of such transformations is directly related to the storage conditions, length of storage, and insect infestation and microflora. The retention of germination capacity and the low increase in free fatty-acid level during the eight months of storage in this experiment is attributable to slow grain metabolism resulting from the low moisture content and relatively stable temperature (27°C). The estimated cost for this kind of storage pit is:

* $us - equals approximately 20 cruzeiros.

It was found that harvested maize with a moisture content of 12 per cent, fumigated and stored in an underground pit lined with a plastic sheet, retained good characteristics during a storage period of eight months. When the pit was opened, the maize was found to have its natural colour, odour, and texture. There were no changes in either moisture content or germination capacity. The small chemical changes observed did not damage the quality of the oil in the stored maize.

2. Aerobic Storage for Preservation of Soybeans in Silos

Brazil is the world's second largest producer of soybeans, with a production of 12.5 million metric tons in the 1976/77 harvest. In contrast to the widely disseminated maize production, the production of soybeans is concentrated in the southern part of the country, where only two estates produce more than 80 per cent of the total soybean crop. The evolution of soybean production has occurred largely over the past six years, with the area cultivated increasing from 1.3 million hectares in 1970 to 6.6 million hectares in 1977. The average yield increased from 1143 kg/ha to 1760 kg/ha in the same period. Soybean production is increasing in Brazil because it is teased on modern agricultural technology, it uses genetically sound seed, and is carried out primarily on very large farms. However, from the beginning, there was an obvious lack of an infra-structure to store this huge volume of soybeans.

Co-operatives were organized and, through government help, existing storage facilities were improved and new ones were built. Large silos began to appear with a capacity for storing from 30,000 to 100,000 metric tons of soybean in bulk. To maintain the quality of the stored soybeans, aeration systems were installed to force air through the silos and avoid the risk of rapid aging caused by rising temperature.

Research work was carried out at ITAL with two metal cylindrical silos, one aerated, one not. After six months in the aerated silo the beans had a better quality than those stored in the non-aerated one. The humidity level dropped from 12.7 to 10 in the same period in the aerated silo. The free fatty-acid content (as oleic acid) in the beans rose from 0.3 - 0.4 to 0.6 - 0.7 after ten months of storage in the aerated unit, while it reached a level of 1.2 to 1.3 in the beans stored for ten months in the non aerated unit.

This year in the State of Paraná, silos are under construction that will hold 40,000 metric tons of soybeans. These silos are being coupled with an aeration system powerful enough to provide a current of air at the rate of 10 me/ in/ton Soybeans should enter the units with 16 per cent humidity and lose 2 per cent after four months of storage. The average yearly temperature and relative humidity for Paraná are 22 C and 8 per cent, respectively, with large deviations.

Soybeans in non-aerated silos have been found to have a moisture content of 12 per cent.

If, by introducing aeration to the storage system, we can r, consistently maintain a 14 per cent moisture content in soybeans, this would mean a gain in weight of 0.02 x 40,000, or 800 metric tons. With a market price of soybeans at $US 200/ton, 800 x $US 200 = $US 160,000. This saving would be enough to pay for installation of the aeration system, which costs about $US 100,000.

The above data show that in the case of soybean storage, aerated silos may be the appropriate technology to adopt in order to avoid losses in both quantity and quality of a crop that has a high monetary value.

3. Storage of Fruits in Cold Maturation Rooms with Controlled Atmosphere

Storing Tahitian and Sicilian lemons at low temperature in a controlled atmosphere containing gibberellic acid showed that the fruit could be kept for at least six months with minimum weight losses.

Similar studies were made with avocados. Methods for proper storage and ripening of bananas, and post-harvest control of fungi that attack mangoes have also been successfully developed and contribute significantly to minimize post-harvest losses of these fruits.

Some studies have been done for private companies, mainly on installation of storage and cooling chambers for fruits and vegetables.

Although horticultural crops may not be considered to be as important as grain crops, their nutritional and economic values should not be neglected.

CONCLUSIONS

ITAL's experience in Brazil and through bilateral projects with other countries has led us to the following conclusions.

1. Post-harvest technology from developed countries can be more easily adapted in developing countries than industrialized agricultural technology can.
2 Government programmes related to post-harvest handling, and government extension services, can help to transmit post-harvest technology to the final user.
3. International co-operation for post-harvest technology transfer can be more effective when research institutes are directly involved.
4. Improvements in post-harvest handling would greatly benefit the final consumer in terms of product quality, price, and availability of food.

Contents - Previous - Next