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Despite the remarkable progress made in increasing food production at the global level, approximately half of the population in the Third World does not have access to adequate food supplies. There are many reasons for this, one of which is food losses occurring in the post-harvest and marketing system. Evidence suggests that these losses tend to be highest in those countries where the need for food is greatest.
Both quantitative and qualitative food losses of extremely variable magnitude occur at all stages in the post-harvest system from harvesting, through handling, storage, processing and marketing to final delivery to the consumer. Although the subject of food losses had been on the agenda of many meetings, it was not until the 1974 World Food Conference and the 7th Special Session of the UN General Assembly that special attention was given to it. In response, the 1977 FAO Conference approved the establishment of a Special Action Programme for the Prevention of Food Losses. Initially, this programme focused on staple food grains but, since 1983, at the request of the FAO Conference, additional attention has been given to perishable food commodities: roots and tuber crops, fruits and vegetables.
As part of this programme, FAO has organized numerous regional, subregional and national workshops and training sessions to help technical officers to recognize and reduce post-harvest losses and enhance the efficiency of marketing operations. In 1985, a training manual (FAO Training Series No. 10, to be revised and reissued as FAO Training Series No. 17/1) on the prevention of post-harvest food losses in grain crops was published. The present manual, on the prevention of post-harvest food losses in fruits, vegetables and root crops, is based on material previously developed during FAO's training programmes and is now being published as a companion to the volume on grain crops in the FAO Training Series. This manual also complements and updates FAO's Marketing Guide No. 2, Marketing Fruits and Vegetables.
I trust that this manual will be of assistance to all those providing practical training for the prevention of post-harvest food losses in perishable crops.
This manual, Volume II of the training manual on the prevention of post-harvest food losses, presents material from a wide variety of disciplines associated with the prevention of food losses and development of marketing operations, particularly those in fruit, vegetables and roots and tubers. It is directed to field staff, project supervisors, teachers at agricultural schools and at training institutions, and extension personnel connected with the handling and marketing of those commodities.
This manual should serve as a reference work on the prevention of post-harvest food losses. For specific training purposes, the manual takes up a number of crops and techniques from which the trainer can select according to local conditions. Trainers are encouraged to supplement the material by practical work and by detailed worksheets or handouts covering special topics of local interest.
Time and money are required to cultivate food products, and unless the farmer is providing food only for his own household, he automatically becomes part of the market economy: he must sell his produce, he must recover his costs, and he must make a profit.
Estimates of the post-harvest losses of food grains in the developing world from mishandling, spoilage and pest infestation are put at 25 percent; this means that one-quarter of what is produced never reaches the consumer for whom it was grown, and the effort and money required to produce it are lost-forever. Fruit, vegetables and root crops are much less hardy and are mostly quickly perishable, and if care is not taken in their harvesting, handling and transport, they will soon decay and become unfit for human consumption. Estimates of production losses in developing countries are hard to judge, but some authorities put losses of sweet potatoes, plantain, tomatoes, bananas and citrus fruit sometimes as high as SO percent, or half of what is grown. Reduction in this wastage, particularly if it can economically be avoided, would be of great significance to growers and consumers alike.
Factors affecting post-harvest food losses of perishables vary widely from place to place and become more and more complex as systems of marketing become more complex. A farmer who is growing fruit for his family's consumption probably doesn't mind if his produce has a few blemishes and bruises. If he is producing for a market at any distance from his own locality, however, he and his workers, if he has any, must have a different attitude if he hopes to get the best money return on his work.
Figure 1. Principal marketing and distribution channels for fresh fruit, vegetables and root crops
By knowing his market, the grower can and must judge how important are the requirements of appearance, maturity and flavour for his produce. Furthermore, the grower must decide whether the investment in packaging will in fact pay for itself in increased value of the crop. It will be of no value to buy expensive containers for his produce if the field hands pitch them around and damage the contents. It is more important for the grower to change the attitude of himself and his workers toward reducing post-harvest losses than it is for him to think that buying fancy packaging will automatically solve his problems and improve his income. The farmer must give careful attention to:
The following sections will discuss these among other factors. The grower must recognize that small changes in attitudes toward the prevention of post-harvest food losses may profit him more than changes in the techniques of the marketing chain, whether containers or transport improvements, and may cost him less in the long run. He must instruct his family, field workers, and others in the methods of reducing his losses.
Most people eat a mixed diet of foods from plants and animals. In most societies, starchy staple foods, particularly cereal grains, are the main source of energy in the human diet. In certain areas, especially in the humid tropics, root and tuber crops, together with plantains and similar plants, are either the staple food or a supplement to cereal staples.
Fruit and vegetables are important sources of essential minerals and vitamins in the human diet. When eaten together with some root (potato, sweet potato) and leguminous (pigeon peas, beans, lentils) crops, they provide a proportion of protein requirements as well as variety in flavour and colour.
The keeping and the preparation of fresh produce after harvest affects its nutritional value in several ways, for example:
Further information on the food value of fresh produce can usually be obtained at national nutritional councils or departments of health.
TABLE 1. Vitamins supplied by fruit, vegetables and root crops
|From carotene in dark green leaves, tomatoes, carrots, papayas
|Pulses, green vegetables, fruit (cereal grains have B. in germ and outer-seed coat)
|Green leafy vegetables and pulses
|Niacin (nicotinic acid)
|Dark green leaves, broccoli, spinach, beets, cabbage, lettuce, avocados
|Dark green leaves, spinach, cauliflower, sweet pepper, citrus, guava, mango, papaya
Source J. Srhuur, FAOR, Barbados.
The overall quality and condition of fresh produce cannot be improved after harvest. The final potential market value of his produce depends on the grower's decisions on what and when to plant and on the subsequent cultivating and harvesting practices. The adoption of good post-harvest practices described in the later sections of this manual can extend the useful post-harvest life of fruits and vegetables but only to the extent that their quality and condition at harvest permit.
Growers in general rely on their own experience and local traditions in selecting crops and in cultivation practices, but if they want or need assistance they may need to be referred to agricultural extension officers or possibly to research and development specialists of their national department of agriculture or its equivalent.
Market factors affecting farmers' decisions on the growing of specific crops are:
A commodity can be "too good" as well as "too bad": one that greatly exceeds market requirements may not bring higher prices and thus be a waste of labour and resources.
An important limitation of most markets is that only certain varieties of a commodity are traded and others are unacceptable. In Indonesia, for example, 242 varieties of mango have been recorded by the Agricultural Seed Experiment Station in East Java, but only seven have any commercial potential beyond certain villages. The non-marketable mangos, however, constitute about 70 percent of the total production, and the local grower can effectively increase his market share only by replacing existing trees with those of the desirable varieties.
In international trade, this specification of variety is of critical importance. Countries wishing to export have little choice but to offer what will be bought by importing countries. This holds true among developing countries. For example, the Association of South East Asian Nations (ASEAN) has consciously promoted trade in fruit and vegetables, many of which are common in the various countries, but there are still distinct preferences for different cultivars between countries.
New varieties are not easily introduced into developing countries and established as profitable crops. Apart from physical conditions and cultivation practices, problems may include the overcoming of traditional human conservatism unless there are compelling economic incentives.
Pre-harvest production practices may seriously affect post-harvest returns in quality and quantity and result in the rejection or downgrading of produce at the time of sale. Some of them are:
3.3.1 Water supply (Irrigation). Growing plants need a continuous water supply for both photosynthesis (the process by which plants convert light to chemical energy and produce carbohydrates from carbon dioxide and water) and transpiration (the giving off by a plant of vapour containing waste products). Bad effects can be caused by:
3.3.2 Soil fertility, use of fertilizers. Lack of plant foods in the soil can seriously affect the quality of fresh produce at harvest. On the other hand, too much fertilizer can harm the development and post-harvest condition of produce. Some of the effects are:
These are a few of the commoner soil-nutrition problems that can be readily identified at harvest. The problem of fertilizer balance in soils and its effect on crops is complex and depends also on other conditions such as temperature, moisture, acidity of the soil and reactions among different fertilizer chemicals. Severe soil-nutrition problems need reference to specialist advice, if available.
3.3.3 Cultivation practices. Good crop husbandry is important in achieving good yields and quality of fresh produce. Certain aspects are particularly important, such as:
3.3.4 Agricultural chemicals. These are of two types:
A critical time for growers of fruit and vegetables is the period of decision on when to harvest a crop. Normally any type of fresh produce is ready for harvest when it has developed to the ideal condition for consumption. This condition is usually referred to as harvest maturity. Confusion may arise because of the word maturity since, in the botanical sense, this refers to the time when the plant has completed its active growth (vegetative growth) and arrived at the stage of flowering and seed production (physiological maturity) as shown in Figure 3.1. Harvest maturity thus refers to the time when the "fruit" is ready to harvest and must take into account the time required to reach market and how it will be managed en route. This time lag usually means that it is harvested earlier than its ideal maturity.
3.4.1 How is harvest maturity identified? Most growers decide when to harvest by looking and sampling. Judgements are based on:
Experience is the best guide for this kind of assessment. Newcomers to fresh produce-growing may find that learning takes time. Harvest maturity can readily be observed in some crops: bulb onions when their green tops collapse and potatoes when the green tops die off. Other crops can be more difficult: avocados remain unripe off the tree after maturity.
Figure 3.1 The comparison of physiological and harvesting maturity is shown here. In the various crops. harvesting maturity may be at a very different stage of the plant's development from that of physiological maturity. (Source: Improvement of post-harvest fresh fruits and vegetables handling, FAO(RAPA)/AFMA, Bangkok, 1986)
Large-scale commercial growers combine observation with more sophisticated measurement:
The final decision on harvesting will take account of the current market value of the expected yield, and also the time during which the crop will remain in marketable condition. With seasonal crops, growers are often tempted to harvest too early or too late in order to benefit from higher prices at the beginning and end of the season.
All fruits, vegetables and root crops are living plant parts containing 65 to 95 percent water, and they continue their living processes after harvest. Their post-harvest life depends on the rate at which they use up their stored food reserves and their rate of water loss. When food and water reserves are exhausted, the produce dies and decays. Anything that increases the rate of this process may make the produce inedible before it can be used. The principal causes of loss are discussed below, but in the marketing of fresh produce they all interact, and the effects of all are influenced by external conditions such as temperature and relative humidity.
An increase in the rate of loss because of normal physiological changes is caused by conditions that increase the rate of natural deterioration, such as high temperature, low atmospheric humidity and physical injury. Abnormal physiological deterioration occurs when fresh produce is subjected to extremes of temperature, of atmospheric modification or of contamination. This may cause unpalatable flavours, failure to ripen or other changes in the living processes of the produce, making it unfit for use.
Careless handling of fresh produce causes internal bruising, which results in abnormal physiological damage or splitting and skin breaks, thus rapidly increasing water loss and the rate of normal physiological breakdown. Skin breaks also provide sites for infection by disease organisms causing decay.
All living material is subject to attack by parasites. Fresh produce can become infected before or after harvest by diseases widespread in the air, soil and water. Some diseases are able to penetrate the unbroken skin of produce; others require an injury in order to cause infection. Damage so produced is probably the major cause of loss of fresh produce.
The influences of all three causes are strongly affected by the various stages of post-harvest operations, discussed below. Furthermore, they all have great effect on the marketability of the produce and the price paid for it.
Commodities entering the trade in fresh produce include a wide variety of plant parts from a large number of plant families and species. The words fruit, vegetables and root crops have no real botanical meaning but are terms of convenience used for horticultural and domestic purposes. As commodities, however, they may be conveniently grouped in relation to the type of edible plant parts, their response to post-harvest handling and their storage characteristics.
4.5.1 Roots and tubers. These are underground parts of plants, adapted for the storage of food materials. They are the means by which the crop survives unfavourable seasonal conditions, and they provide the food reserve enabling the plant to make rapid growth when conditions are favourable. They include:
|Swollen stem tuber
|Irish or white potato
|Compressed stem tuber (corm)
|Dasheen, tannia, eddoe
|Root tuber (from fibrous root)
|Root tuber (from main tap-root)
In most of these, the stored food material is starch, but in some tap-root tubers, such as carrots, it is mostly sugars.
Figure 4.1 Roots and tubers
4.5.2 Edible flowers. Plant breeders have produced various vegetables with dense massed flower heads that can be eaten when the flowers are immature buds. These have long been popular in temperate countries but in recent years have become well-known in the tropics, where cultivars that can be grown in warm conditions or at higher altitudes have been developed. In contrast to the massed flower head, the pineapple, one of the most widely produced tropical fruits, is formed by the fusion of a mass of immature and unfertilized flowers clustered around the plant's main stalk, which becomes the core of the fruit. Examples of such flowers are:
|Massed flower heads
|Fused mass comprising unfertilized flower parts and main flower stalk
4.5.3 Vegetative growth (leaves, stems, shoots). These common green vegetables are important sources of minerals, vitamins and fibre (roughage) in the diet. They vary greatly, but typical examples are:
|Whole above-ground vegetative growth (before flowering)
|Dasheen (callaloo), spinach
|Swollen leaf base
|Onions (including dry bulb onions), leeks
4.5.4 Reproductive structures. These are fleshy, seed-bearing structures eaten principally for their fleshy parts. They are mostly well-known fruits having a high sugar content when ripe and are normally eaten at that stage. Some, such as tomatoes and peppers, are used as salads or vegetables. In addition, some vegetables, such as immature green seed pods of some crops, are eaten before the seeds harden.
Figure 4.2 Edible flower structures
In a few crops the immature seeds only are eaten:
|Fleshy fruits with single seed (drupe)
|Mango, avocado, plum
|Fleshy fruits with several seeds
|Tomato, citrus (orange, grapefruit, mandarin, lime), cucumber, pepper, aubergine, banana
|Immature green pods with partly developed seed
|Green beans, yard-long beans (asparagus bean, bodi), okra
|Immature seed only
|Pigeon pea, green pea
Most of these examples are indigenous to the tropics and subtropics and are chilling-sensitive when held in storage.
Growing green plants use the energy provided by the sunlight falling on their leaves to make sugars by combining carbon dioxide gas from the air with water absorbed from the soil through the roots. This process is known as photosynthesis. The plant either stores these sugars as they are or combines the sugar units into long chains so that they form starch. The sugars and starches, known as carbohydrates, are stored in various parts of the plant and are used later to provide the energy for its further growth and reproduction. Starches are stored by root crops over the dormant period to supply the energy for renewed growth when dormancy ends. The energy for growth in both cases is released by the process of respiration, which occurs in all plant parts before and after harvest.
What is the normal pattern of activity of fresh produce after harvest? How is this activity affected by conditions after harvest, and what effect does this have on losses?
Figure 4.3 Vegetative structures
We referred earlier to physiological deterioration as one of the causes of post-harvest loss in fresh produce. The word physiology means the study of processes that go on within living things. When fresh produce is harvested, these processes of living continue, but in modified form. Because the crop can no longer replace food materials or water, it must draw on its stored reserves, and as these are used up, the produce undergoes an ageing process that is then followed by breakdown and decay. Even if produce is not damaged or attacked by decay organisms, it will eventually become unacceptable as food because of this natural rot. The principal normal physiological processes leading to ageing are respiration and transpiration (Figure 4.5).
Figure 4.4 Reproductive structures (fruits)
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