GENERAL POSTHARVEST CONSIDERATIONS 

All fruits, vegetables and root crops are living biological organisms, having a respiratory system, similar to that of humans. They continue their living processes after harvest. Respiration is the process by which plants take in oxygen and give out carbon dioxide. On the basis of their respiration rate and ethylene production patterns during maturation and ripening, fruits can be classified in two groups: climacteric fruits (they exhibit a large increase in carbon dioxide and ethylene production rates coincident with their ripening) and non-climacteric fruits (which exhibit no changes in their generally low carbon dioxide and ethylene production rates during ripening). In accordance with the respiration rate most horticultural commodities can be classified as follows:

 • Low respiration rate. Nuts, dates, dried fruits and vegetables, apples, citrus, grape, garlic, onion and sweet potato. 

• Moderate respiration rate. Banana, cherry, plum, cabbage, carrot, lettuce, pepper and tomato. 

• High respiration rate. Cauliflower, avocado, berries and green onion. 

• Extremely high respiration rate. Broccoli, peas, spinach and sweet corn. 

Ethylene 

Ethylene is a natural product of plant metabolism and is produced by all tissues of higher plants. It is considered the natural aging and ripening hormone and is active even at small traces. Horticultural commodities can be classified as follows, based on the amount of ethylene they produce: 

• Low ethylene production. Cauliflower, cherry, citrus, leafy vegetables, root vegetables, potato, cucumber, eggplant, pepper, pineapple, pumpkins and watermelon. 

• Moderate ethylene production. Banana, guava, honey dew melon, mango, plantain and tomato. 

• High and very high ethylene production. Apples, avocado, cantaloupe, papaya, kiwi, pear, plum, passion fruit, sapote and cherimoya. 

Fruits, vegetables and root crops contain 65 to 95 percent of water and their post harvest life depends on the rate at which they use up their stored food reserves and their rate of water losses. When food and water reserves are exhausted the produce dies and decays. 

Objective of post-harvest handling 

Both quantitative and qualitative losses occur at all stages in the post-harvest handling system of the distribution chain of perishables (from harvesting, through handling, packing, storage and transportation to final delivery of the fresh produce to the consumer). Factors affecting post-harvest losses vary widely from place to place and are more and more difficult. A farmer growing fruits for his family’s consumption does not mind too much if his produce has a few bruises and scars and if it is not packed for a suitable transportation to a market at a certain distance. Meantime if he is producing for the market at any distance from his own farm he must have a different attitude if he wants to get the best return from his produce: he mast know about the quality requirements wanted by the consumers and the proper containers needed for the transport. 

Two examples below help to explain the importance of post-harvest handling. Example 1. By knowing the market and its needs, the grower can and must judge how important are the requirements of appearance, maturity and flavor of his produce for the consumer .Those requirements are strictly related with maturity indexes, which are influenced by a proper harvesting time. A farmer must, therefore, know the proper harvesting time for his produce. 

Example 2. The farmer must decide whether the investment in packaging will increase his revenue from the crop. It will be of no value to buy expensive containers for his produce if the harvesting is not properly done and bruises and scars damage the content before packaging. It is more important for the grower to change his attitude toward reducing post-harvest losses, through improving harvesting, than to think that the purchase of expensive packages will automatically solve his problem and increase his income. The objective of post-harvest handling is, therefore, the creation of an understanding of all the operations concerned from harvesting to distribution so as to enable people to apply the proper technology in each step and in such a way to minimize losses and maintain quality as high as possible during the distribution chain. The farmer must give, among others, special and careful attention to the following steps of the post-harvest chain: 

-Market demand for the produce they are planning to grow. 

-Market requirements and buyers; -Knowledge of the fresh produce.  

-Cultivation practices. 

-Factors affecting post-harvest deterioration. 

-Harvesting and field handling; -Packing in the field. 

-Handling and packing in the packing house. 

-Common storage and refrigeration. 

-Transport. 

-Sale to agents, traders or consumers. 

-Market handling, and 

-Shelf-life of the produce. 

The first part of this manual was prepared as an overview of the general principles and operations involved in the post-harvest handling and storage of fresh fruits, vegetables and root crops. The second part of the manual is centered to the specific handling and distribution operations of fruits, vegetables and root crops grown in Grenada. This document has been produced for use, along with other material, as a training component for concerned government and private sector persons interested to understand the principles of post-harvest and its applications to the fresh commodities marketed within the country and overseas. 

1.2. Post-harvest technology procedures Temperature and humidity are used to control shelf-life of commodities in refrigerated cold stores. 

1.2.1. Temperature management practices Temperature management is the most important tool that we have to extend shelf-life of fresh horticultural commodities after harvesting the produce. Temperature management begins with a rapid removal of the field heat by using one of the following cooling methods: 

• Hydro cooling. 

• In package ice. 

• Top icing. 

• Evaporative cooling. 

• Room cooling. 

• Forced air cooling. 

• Serpentine forced air cooling. 

• Vacuum cooling; and 

• Hydro-vacuum cooling. 

Cold storage facilities should be well constructed and adequately equipped. They should have: 

• Good construction, and insulation and vapor barrier. 

• Strong floor. 

• Adequate doors for loading and unloading. 

• Effective distribution of refrigerated air. 

• Properly located controls. 

• Enough refrigerated coil surface. 

• Capacity adequate to expected needs. 

• Appropriate stacking of the produce. 

1.2.2. Control of relative humidity Appropriate relative humidity is important to control the following: • Water losses; • Decay development; • Incidence of some physiological disorders; • Uniformity of ripening. Proper relative humidity should be 85-95% for the majority of the fruits, 95-98% for vegetables (except dry onions and pumpkins at 70-75%) and 95-100% for some root vegetables. Relative humidity can be controlled by the following methods: 

• Addition of moisture to air by humidifiers. 

• Regulation of air movement in relation to produce. 

• Maintaining coil temperature to 1˚C difference to air temperature. 

• Wetting the floor in the storage room; and 

• Addition of crushed ice. 

1.2.3. Controlled atmosphere Controlled atmosphere means the addition or removal of gases resulting in an atmospheric composition surrounding the commodity that is different from that of the air 79% of nitrogen, 21% of oxygen and traces of carbon dioxide). Usually this involves reduction of oxygen and elevation of carbon dioxide, in a perfectly sealed room. The use of controlled atmosphere can be considered only as a supplement to the proper temperature and humidity procedures. Controlled atmosphere is used for a certain number of crops to extend shelf-life, reduce disorders such as chilling injuries, reduction of pathogens and some insect control. 

1.2.4. Supplemental procedures 

The following treatments may be applied to horticultural commodities: 

• Curing of certain roots, tubers and bulbs vegetables (see details on specific chapter); 

• Sorting for defect elimination. 

• Waxing and other surface coatings. 

• Hot water treatment; 

• Treatment with post-harvest fungicides or bactericides. 

• Use of sprout inhibitors. 

• Special post-harvest chemical treatment. 

• Fumigation for insect control. 

• Films wrapping; and 

• Ethylene treatment for de-greening and ripening certain fruits, such as citrus, bananas and mangos. 

Details are given in the specific chapters. 

1.2.5. Ripening fruits with ethylene gas 

In the post-harvest physiology of most horticultural crops, ethylene plays an important role, sometime beneficial (improving quality of the produce by faster and more uniform ripening prior to retail distribution) and often deleterious (increasing the rate of senescence and reducing shelf-life). Systems for ethylene treatments. Handlers can equip existing rooms for use as ripening chambers or they can install specially built ones. Both need automatic control of temperature (for heating and cooling), humidity and ventilation. The room should be as tight as possible, to prevent leakage of gas, but not essentially hermetically sealed. Amount of gas needed. It is recommended100 ppm of gas. Higher concentration will not speed up the ripening process. Too much gas may result an explosive air gas mixture. Safety precautions have to be followed. Temperature and humidity. Optimum temperature varies from 18 to 25˚C. At lower temperature ripening is slowed, from 25 to 30˚C ripening may be inhibited and decay accelerated. Relative humidity should be as high as possible. 

Other technologies for using ethylene. Fruits ripening could also be induced with the following methods: 

• Explosion-proof ethylene mixed with an inert gas. 

• Ethylene generators, widely used in developed countries. 

• Ethephon. 

• Calcium carbide which, in a furnace, releases acetylene (which has an ethylene like response) when combined with water. 

• Fruits already ripe (included in the high ethylene producing category) can be used in very small commercial operations, or at home, to ripen other fruits. 

Deleterious effect of ethylene. The potent effect of ethylene on senescence of perishables commodities can greatly reduce the shelf-life of product sensitive to it. Techniques to remove it (such as the utilization of potassium permanganate, ozone, hypobaric storage and oxidizers) or reduce its effect (such as loss of green color in certain vegetables, accelerate ripening, sprouting and decreased shelf-life) are of considerable importance. Storage of perishables sensitive to the gas should not be done in the same room where products which have a high or very high production of ethylene are kept. See more details in the first part of this chapter. 

1.3. Postharvest deteriorations The interaction of metabolic and environmental factors are responsible for many post-harvest deteriorations. Among the main causes of wastage are the following: 

-General senescence; 

-Water loss; 

-Diseases and pests; 

-Physical damages (mechanical injury); 

-Injuries from temperature effects (chilling injuries); and 

-Other causes. 

1.4. Standardization, quality factors, quality standards and quality control Almost all agricultural commodities in developed countries are now marketed on the basis of official standards established under national or international laws. The role of the official standards is particularly important in the case of perishable commodities such as fresh fruits vegetables and root crops. Standardization, as applied to fresh commodities can be described as “common acceptance of the practice of classifying produce and offering it for sale, in term of quality characteristics that have been precisely defined and are constant over the time and distance”. Time and distance are important parameters since produce quality deteriorates with increased time and/or handling. Products that leaves the farm or the packinghouse as Grade 1 may be Grade 2 on arrival at the wholesale or retail market as a result of improper harvesting and handling, bad packaging, rough transport, excessive delays and other malpractices. Definition of quality. The word quality is used in various ways in reference to fresh fruits, vegetables and root crops, such as market quality, edible quality, dessert quality, shipping quality, table quality, nutritional quality, internal quality, and appearance quality. Quality of fresh horticultural commodities is a combination of characteristics, attributes, and properties that give to the commodity value to humans for food (fruits, vegetables and root crops). Producers should be concerned that their commodities have good appearance and few visual defects, but for them a useful cultivar must have high yield, disease resistance, easy to harvest and shipping quality. To receivers and market distributors, appearance quality is most important, followed by firmness and shelf-life. 

Consumers consider good quality, fruits and vegetables which look good, are firm, and offer good flavor, good edible quality and nutritive value. Quality components. The various components of quality are used to evaluate commodities in relation with specifications for grades and standards, and evaluation of responses to various environmental factors and post-harvest treatments. The relative importance of each factor depends upon the commodity and its intended use, fresh or processed. The main components are: • Appearance. Many defects can influence the quality appearance of horticultural crops. Morphological defects are sprouting of potatoes, onions and garlic, rooting of onions, germination inside tomatoes and peppers, floret opening in broccoli, etc. Physical defects include shriveling and wilting of all commodities, internal drying of some fruits, mechanical damage such punctures, cuts and scratches, spitting and crushing, skin abrasions, deformation and bruising. Temperature related disorders (such as sunburn, chilling, sunscald), blossom end rot. Pathological defects include decay provoked by fungi and bacteria. • Texture. It is important for eating and cooking quality. • Flavor. Evaluating flavor quality involves perception of taste and aroma. • Nutritive value. Fresh fruits and vegetables play an important role in human nutrition, especially as a source of vitamins, minerals and dietary fibers. Physical damage may reduce the nutritive value of a commodity. • Safety. Safety factors include the presence of toxicants such as the greening of potatos, chemical residues and mycotoxine produced by fungi. Factors influencing quality. Many pre and post-harvest factors influence the composition and quality of fresh horticultural crops. They may include: • Genetic factors: cultivar selection and rootstocks; • Pre-harvest environmental factors: climatic conditions, cultural conditions and time and method of harvesting; • Harvesting: maturity, ripeness, physiological age; • Post-harvest treatments: handling methods, storage time between harvesting and consumption; and • Interaction among the above detailed factors. Some form of grading and quality control is always carried out whenever fruits, vegetables and root crops are traded. The most basic quality standard is that the produce must be edible, so severely diseased or badly damaged produce is not accepted even in the simplest market. Other quality requirements vary depending on the stage of development of the market and personal preferences of the consumers and become more and more complex as the economic prosperity of the community where the produce is traded increases. 1.4.1. Important quality components 13 Attributes of produce, which are important to consumers and therefore could be incorporated into grading or quality standards, can be grouped under: -Appearance characteristics. The most important quality attributes of fresh fruits and vegetables appearance are: -Size. For most commodities consumers have a definite preference as to the desirable size, which is the most widely used quality parameter. This preference must be expressed as weight, diameter, circumference, length or width. Where produce is graded according to size, it is a normal practice to package those of similar size together. The uniformity of size allows produce to be placed into a container in a regular packing array, with the result firstly to have a more efficient use of packing space so that either more produce can be placed in the container or the size of the container reduced which means a reduction of the cost of packaging per unit of produce. -Shape. While shape differs greatly between commodities, it one of the major recognition factors used by consumers who will place a lower value on a commodity, which lacks the expected characteristic shape. -Color. Many produce show distinctive color changes during maturation which have been correlated by the consumers with the development of other desirable quality attribute so that the correct color of the skin is often the basis for a decision to purchase the commodity displayed on the shelves of the supermarkets. -Conditions. It is a quality attribute usually referring to freshness and stage of senescence or ripeness of a commodity. Factors which detract from the desirability of a commodity include, among others: -Wilting of leafy vegetables; -Shriveling of fruits; -Skin blemishes such as bruises, scratch marks and cuts; -Surface contamination by soil, birds or insects secretions, plant secretions such as latex straining; and -Residues from chemicals applied during the growing season. -Texture and flavor. Texture is the feeling a food gives in the mouth. It is a combination of sensation derived from the lips, tongue, walls of the mouth, teeth and even the ears. Flavor comprises two factors: taste provoked by sugar and acidity of the produce and aroma provoked by volatile organic compound detected by the nose. 1.4.2. Objective quality standards 14 The ideal quality standard is one which can be related to a numerical value derived from a simple test conducted quickly in the field, packing house or market with minimum equipment to establish with a certain accuracy when to harvest, store or consume a produce. The test would mainly be used by farmers to determine when to harvest produce. It could also be used during storage or in the market to ensure that the produce being sold has retained an acceptable eating quality or has a predetermined self-life. Main objective quality standards are: - Color. Research has developed charts for apple, pears and stone fruits. Similar ones are for bananas and tomatoes. -Flesh firmness. The measurement of the texture of the flesh is applied mostly in apples and pears with a penetrometer to establish the proper harvesting time suitable for a long cold storage of the produce. -Soluble solids. The sugar content measured with a refractometer is a suitable maturity index for a number of fruits, such as grapes, melons, pineapples and citrus. Titratable acidity. With the approach of maturity we assist in the reduction of the acidity in the majority of fruits. It is useful for a number of fruits but correct measurement can be done only in a laboratory. -Sugar/acid ratio. The ratio between sugar and acidity is used to assess the acceptability of citrus, pineapple and grapes. 1.4.3. Development of grading standards Developed countries have comprehensive sets of regulations for fruits, vegetables and root crops marketed in the countries themselves or for export. An increasing number of developing countries have developed the same regulations to export their produce to developed ones. The regulations stipulate the market grade classifications which must be used and define in detail the physical characteristics and quality parameters of produce in each grade. They also often specify the type and size of the containers (packages) that can be used, labeling requirements, recommended storage and transport conditions and permitted post-harvest treatments. In most of the countries the regulations are mandatory and in a few of them they are merely guidelines. The regulations usually categorize produce into three or four classes, with the lowest class being considered only just acceptable for marketing. The appearance of the produce in each class is decided on the basis of shape and color, the type and extent of blemishes that can be present and physical characteristic specific to that commodity. Apart from an applicability for export trading, the grading standards used in developing countries are unrealistic for the marketing of fruits, vegetables and roots crops within Grenada. The international standards severely downgrade 15 commodities which show slight cosmetic blemishes and the lowest defined grade excludes a lot of produce that is still of good eating quality. Grading regulations to be used in Grenada for marketing the produce within the country should be established to allow the marketing of the produce at the quality required by the different consumer groups in the country. For example: -Produce sold to the large hotels, restaurants and special tourist stores can benefit by grading to a uniform maturity and size with a low level of blemishes and will require a set of grading standards not necessarily inferior to the international ones. -Produce destined for cheaper priced markets can be of mixed size and maturity and a higher level of blemishes and will require a completely different set of grading standards, allowing the marketing of lower quality produce. Starting grade standards at the farm .The first simple grading which could be introduced at farm level for marketing produce within the country should merely be to codify the informal market practices that are currently in use. Future refinements should be gradual and with the aim at eliminating undesirables and inefficient practices. When a set of regulations have been gradually introduced, it is necessary to conduct an intensive education campaign to ensure that everyone is fully aware of what the changes are and how farmers will benefit from the changes. Starting grade standards for export. Grade standards for export can be introduced only after the introduction of simple but clear grades standards for marketing the produce within the country .The grades standards to be introduced will have to be those established and implemented in the country where the export is planned. Standards should be introduced at trade level or at farm level in case this is well organized. Few exporting countries have established standards, which are even stricter than those prevailing in the importing country. This ensures that only top quality produce is exported. 1.4.4. Quality control Fresh produce is highly perishable and it is natural that some deterioration of quality will occur during the marketing process. The rate of deterioration will depend on the care or abuse exerted on the produce during harvesting, handling, transport and storage. The development of marketing practices and strategies become more important and refined with the development of marketing practices, standardization, market information service and increased competition. Quality control is one of the most important features in achieving consistency and reliability of products, like all aspects of marketing quality control demands good planning, research, and management together with regular training and reviewing of procedures. When standardization practices have been implemented and there 16 is a degree of policy in the market place, there will also be an elementary form of quality control. In the developed countries and also in those developing countries, which operate a regular export service to sophisticated markets, the practice of quality control has become a fundamental part of the production and marketing programme. Monitoring and testing of production practices, for maximum production of produce, which conforms to market demand, is one area where institutional research particularly in Grenada can be of great assistance to the producer, but the producer has the obligation of adhering to guidelines, such as: - At harvest time, the producer must keep a careful check on harvest maturity to ensure that the produce conforms to market and/or storage requirements. - In field packing and transport, the producer must carefully check that the operation is properly conducted to ensure that the produce arrives at the packinghouse or to the market in good condition. - In the packinghouse, the packer needs to keep a close eye on the performance of his staff to ensure that selection and grading practices are adhered to. One of the biggest problems concerning implementation of standardization and quality control in developing countries is the lack of personnel with suitable qualification and experience There is a big scope for countries to send promising staff abroad for training .In addition there is a need for dissemination and training to middle level staff who are already active by organizing practical workshops at the national, district, institutional and school levels. 2. HARVESTING AND FIELD HANDLING Farm management is generally aimed at maximizing the yield of a crop from the area of land under cultivation while at the same time maximizing the return. The time, labor and capital expended in bringing the crop to maturity is rewarded by the financial return obtained by the grower during marketing .For fruits and vegetables the magnitude of this return mainly depend on: -quantity of fresh produce harvested and marketed, which mostly depends on production planning, crop selection, varietal selection ,production practices (which include among other irrigation, cultural practices, fertilization and chemical treatments). -quality attributes to satisfy market and consumer requirements. The overall quality of fresh produce cannot be improved after harvest ,there are a few exceptions like controlled ripening to improve color and flavor and 17 refrigerated and controlled cold storage to extend shelf-life. These exceptions are however limited by pre-harvest conditions. Size. It is the major quality factor and farmers through varietal selection followed by production practices, should try to control it. The aim is to produce a crop of an average desirable size which is not necessarily the largest possible size. Mechanical defects. The need to reduce surface defects is an inevitable consequence of market development. These defects can be physical damages which can be controlled pre-harvest by better plant management to protect the produce from wind, sun, hail, chemical residues, etc. Pest and diseases. A better control with appropriate and controlled application of chemicals and field sanitations practices to control fungal, bacteria and insect attacks and avoid the presence of unsightly marks. Varietal selection. The desired market characteristics of a commodity can often only be obtained by changing the variety being grown. This will often means that growers have the difficult task of adapting to new varieties which may have very different growing characteristics compared to traditional ones. However a resistance to change may mean a major loss of income as the traditional varieties become less popular on the market. 2.1. Harvesting factors The quality and conditions of produce sent to market and their consequent selling price are directly affected by the care taken during harvesting and field handling. Whatever the scale of operations or the resources of labor and equipment available, the planning and carrying out of harvesting operations must observe basic principles. The objective of the grower should be: - to harvest a good quality crop in good condition; - to keep the harvested produce in good condition (protected from rain, sun or animals) until it is consumed or sold; and - to dispose of the crop to a buyer or through a market as soon as possible after harvest. To meet these objectives, success for the harvesting, field handling and marketing must depend on planning from the earliest stages of production, with particular regard to: - crop selection and timing to meet expected market requirements; - contact with buyers so that the crop can be sold at a good price when ready for harvest; 18 - planning harvest operations in good time, arranging for labor, equipment, material, cover space to protect the inputs and the harvested crop and transport; - it is economically sound in terms of returns on investment to improve grading, packing and handling of the produce before it leaves the farm; - considering the above the grower must ensure that all those working on the farm are properly trained; - provide full supervision at all stages of harvesting and field handling. 2.1.1. Maturity at harvest Fruits and vegetables are considered to be commercially mature when at the stage development of that physiological consumers consider to be the most desirable. However the stage, at which a commodity reaches commercial maturity, varies greatly. Many leafy vegetables are commercially mature at an early stage of plant development while fruits are often ready for harvest at a fully developed stage. For details on maturity standards see the following Tables 1 and 2. Figure 1. Harvesting criteria for mango. Immature (a) and mature (b) fruit, with marked shoulders. Does not apply to many varieties. Source: FAO, 1986 Maturity standards have been determined for many fruits and vegetables. Harvesting crops at the proper maturity allows handlers to begin their work with the best possible quality produce. Produce harvested too early may lack flavor and may not ripen properly, while produce harvested too late may be fibrous or overripe and have a shorter shelf-life. Pickers can be trained in methods of identifying produce that are ready for harvest. Table 1, from Reid (in Kader, 1992) provides some examples of maturity indices.