The post-harvest sector includes all points in the value chain from production in the field to the food being placed on a plate for consumption. Postharvest activities include harvesting, handling, storage, processing, packaging, transportation and marketing.
Causes of On-Farm Loss
There are numerous factors affecting post-harvest losses, from the soil in which the crop is grown to the handling of produce when it reaches the shop. Pre-harvest production practices may seriously affect post-harvest returns. Plants need a continuous supply of water for photosynthesis and transpiration. Damage can be caused by too much rain or irrigation, which can lead to decay; by too little water; and by irregular water supply, which can, for example, lead to growth cracks. Lack of plant food can affect the quality of fresh produce, causing stunted growth or discoloration of leaves, abnormal ripening and a range of other factors. Too much fertilizer can harm the development and post-harvest condition of produce. Good crop husbandry is important for reducing losses. Weeds compete with crops for nutrients and soil moisture. Decaying plant residues in the field are also a major loss factor.
Causes of Loss after Harvest
Fruits and vegetables are living parts of plant and contain 65 to 95 percent water. When food and water reserves are exhausted, produce dies and decays. Anything that increases the rate at which a product’s food and water reserves are used up increases the likelihood of losses. Increases in normal physiological changes can be caused by high temperature, low atmospheric humidity and physical injury. Such injury often results from careless handling, causing internal bruising, splitting and skin breaks, thus rapidly increasing water loss.
Respiration is a continuing process in a plant and cannot be stopped without damage to the growing plant or harvested produce. It uses stored starch or sugar and stops when reserves of these are exhausted, leading to ageing. Respiration depends on a good air supply. When the air supply is restricted fermentation instead of respiration can occur. Poor ventilation of produce also leads to the accumulation of carbon dioxide. When the concentration of carbon dioxide increases it will quickly ruin produce.
Fresh produce continues to lose water after harvest. Water loss causes shrinkage and loss of weight. The rate at which water is lost varies according to the product. Leafy vegetables lose water quickly because they have a thin skin with many pores. Potatoes, on the other hand, have a thick skin with few pores. But whatever the product, to extend shelf or storage life the rate of water loss must be minimal. The most significant factor is the ratio of the surface area of the fruit or vegetable to its volume. The greater the ratio the more rapid will be the loss of water. The rate of loss is related to the difference between the water vapour pressure inside the produce and in the air. Produce must therefore be kept in a moist atmosphere.
Diseases caused by fungi and bacteria cause losses but virus diseases, common in growing crops, are not a major post-harvest problem. Deep penetration of decay makes infected produce unusable. This is often the result of infection of the produce in the field before harvest. Quality loss occurs when the disease affects only the surface. Skin blemishes may lower the sale price but do not render a fruit or vegetable inedible. Fungal and bacterial diseases are spread by microscopic spores, which are distributed in the air and soil and via decaying plant material. Infection after harvest can occur at any time. It is usually the result of harvesting or handling injuries.
Ripening occurs when a fruit is mature. Ripeness is followed by senescence and breakdown of the fruit. The category “fruit” refers also to products such as aubergine, sweet pepper and tomato. Non-climacteric fruit only ripen while still attached to the parent plant. Their eating quality suffers if they are harvested before fully ripe as their sugar and acid content does not increase further. Examples are citrus, grapes and pineapple. Early harvesting is often carried out for export shipments to minimise loss during transport, but a consequence of this is that the flavour suffers. Climacteric fruit are those that can be harvested when mature but before ripening has begun. These include banana, melon, papaya, and tomato. In commercial fruit marketing the rate of ripening is controlled artificially, thus enabling transport and distribution to be carefully planned. Ethylene gas is produced in most plant tissues and is important in starting off the ripening process. It can be used commercially for the ripening of climacteric fruits. However, natural ethylene produced by fruits can lead to in- storage losses. For example, ethylene destroys the green colour of plants. Leafy vegetables will be damaged if stored with ripening fruit. Ethylene production is increased when fruits are injured or decaying and this can cause early ripening of climacteric fruit during transport.
Damage in the Supply Chain
Fruits and vegetables are very susceptible to mechanical injury. This can occur at any stage of the marketing chain and can result from poor harvesting practices such as the use of dirty cutting knives; unsuitable containers used at harvest time or during the marketing process, e.g. containers that can be easily squashed or have splintered wood, sharp edges or poor nailing; over packing or under packing of containers; and careless handling of containers. Resultant damage can include splitting of fruits, internal bruising, superficial grazing, and crushing of soft produce. Poor handling can thus result in development of entry points for moulds and bacteria, increased water loss, and an increased respiration rate.
Produce can be damaged when exposed to extremes of temperature. Levels of tolerance to low temperatures are importance when cool storage is envisaged. All produce will freeze at temperatures between 0 and -2 degrees Celsius. Although a few commodities are tolerant of slight freezing, bad temperature control in storage can lead to significant losses.
Some fruits and vegetables are also susceptible to contaminants introduced after harvest by use of contaminated field boxes; dirty water used for washing produce before packing; decaying, rejected produce lying around packing houses; and unhealthy produce contaminating healthy produce in the same packages.
Losses directly attributed to transport can be high, particularly in developing countries. Damage occurs as a result of careless handling of packed produce during loading and unloading; vibration (shaking) of the vehicle, especially on bad roads; and poor stowage, with packages often squeezed into the vehicle in order to maximise revenue for the transporters. Overheating leads to decay, and increases the rate of water loss. In transport it can result from using closed vehicles with no ventilation; stacking patterns that block the movement of air; and using vehicles that provide no protection from the sun. Breakdowns of vehicles can be a significant cause of losses in some countries, as perishable produce can be left exposed to the sun for a day or more while repairs are carried out.
At the retail marketing stage losses can be significant, particularly in poorer countries. Poor-quality markets often provide little protection for the produce against the elements, leading to rapid produce deterioration. Sorting of produce to separate the saleable from the unsaleable can result in high percentages being discarded, and there can be high weight loss from the trimming of leafy vegetables. Arrival of fresh supplies in a market may lead to some existing, older stock being discarded, or sold at very low prices.
Ghana currently loses GHc700, 000 every year in post-harvest losses because of poor post-harvest management practices in the country.
According to Dr. Joe Oteng-Adjei, former Minister for Environment, Science, Technology and Innovation, the country also loses between 20 and 50 per cent of all vegetables, fruits, cereals, roots and tubers produced each year, while it struggles to achieve food security and eradicate hunger.
The Ghana Atomic Energy Commission Gamma Irradiation Facility
The Gamma Irradiation Facility (GIF) was initially acquired by Ghana Atomic Energy Commission (GAEC) under an International Atomic Energy Agency (IAEA) Technical Assistance Programme in 1994 and commissioned in 1995 with a source loading of 50 kCi. The facility was upgraded in 2010 with financial assistance from the Export Development and Investment Fund.
The GIF is a category IV wet storage irradiator with a Cobalt-60 source (50 kCi as at 2010) and has a maximum loading capacity of 500 kCi. A pneumatic hoist mechanism carries the plaque source (1x1m2) from the rest position to the irradiation position in the irradiation chamber. When it is not in use, the Cobalt-60 source is stored in a water pool of dimension 2x3x5.7m. A de-ionising unit monitors and purifies the pool water.
A product transport system conveys product between the storage area and irradiation chamber by means of a tote boxes moved by a tote box car. There are 13 tote boxes and their movement is regulated by the control system.
The operations of the irradiator are carried out from a control system consisting of a PC-PLC based electronic unit. The system operates with a software that controls the detectors, ventilation system, pressurised air system and mechanical units.
Sequentially interlocked controls are provided for personnel access, radiation chamber lockup sequence and source exposure operations, thus enhancing safety to operators.
Irradiation of Food and Agricultural Produce
What is Food Irradiation?
Irradiation is a process that exposes food to ionising energy for a specific length of time, depending on the purpose of treatment. The process of food irradiation ensures the destruction of bacteria, fungi, insects and other parasites that cause food spoilage and disease. The radiation treatment also prevents germination and sprouting in some foods while delaying ripening and senescence in others. Food irradiation does not cause significant changes in the chemical composition, nutritional value, taste or appearance. Since food irradiation is a physical process, it does not leave any residues in the treated food products.
Due to the penetrating power of irradiation, food irradiation can be an end process, that is, the food is irradiated in its final package; thus preventing post-irradiation contamination.
Health and food safety authorities have evaluated irradiation and determined that it is safe and effective. Irradiation has been more extensively studied and evaluated in respect to food safety other technologies such as canning, freezing, and chemical additives.
Extensive research has determined that nutritional content, flavour, taste and consistency of foods do not change significantly during irradiation. Health and food safety authorities in more than 40 countries have approved irradiation of more than 40 different food products.
Food is irradiated in a special processing facility where it is exposed to gamma rays, electron beams or x-rays. The food is monitored to assure that the exact treatment level is achieved.
The quantity of ionising energy absorbed by the product is called the ‘Dose’, measured in kGy (kilo Grays). 1 Gy corresponds to 1 Joule of energy absorbed by 1 kilogram of matter.
Unique advantages of the technology include:
Total penetration of final packaging
‘Cold process’- no temperature influence
Time/dose is the only variable –easy validation and control
No quarantine time
Safe process; no residues, no radioactivity induced
Can be applied at various stages of manufacturing process
Benefits of irradiation include:
Destruction of harmful bacteria, fungi and parasites that cause disease
Destruction of insects and their larvae in cereals, fruits and vegetables
Delaying ripening and senescence of fruits and vegetables to extend freshness
Preventing /inhibition of sprouting in tubers, bulbs, rhizomes.
Elimination of internalised pathogens on fresh vegetables.
Radiation Sterilization for Medical, Pharmaceutical and Cosmetic Industries
What is Radiation Sterilization?
Radiation sterilisation is the exposure of medical items, pharmaceutical and cosmetic raw materials to ionising energy for the purpose of achieving sterility. Radiation sterilization improves the hygienic quality of medical items and devices as well as that of pharmaceuticals and cosmetic materials. The sterility of products is maintained for as long as the packaging is intact. The process is more efficient and also safer than the conventional sterilization processes such as autoclaving and fumigation by gas (ethylene oxide).
It is a well-established technology in many countries and achieves higher sterility assurance levels compared to conventional processes such as autoclaving and fumigation. Sterilisation with ethylene oxide during fumigation causes pollution and its residue is carcinogenic thus creating thus creating health and safety concerns. The global healthcare industry is adopting radiation sterilization since it is safe, simple, environmentally friendly and cost-effective. There are over 200 gamma irradiators and 1200 accelerators in operation in approximately 55 countries worldwide.
The item is sterilised in a special processing facility where it is exposed to gamma rays, electron beams or x-rays. The item is monitored to assure that the sterilisation dose of 25 kGy is achieved.
All bacteria, moulds and viruses are susceptible to ionising radiation. The DNA and other organelles in microorganisms are destroyed by ionising radiation thus causing malfunctioning and eventual cell death.
The quantity of ionising energy absorbed by the product is called the ‘Dose’, measured in kGy (kilo Grays). I Gy corresponds to 1 Joule of energy absorbed by I kilogram of matter.
Unique advantages of the technology include:
provides high sterility assurance levels of 10-6
treated product can be used immediately without quarantine time
insignificant rise in product temperature during the process, thus preserving heat-sensitive plastics and other components
high penetrability (hence packaged product can be processed)
very precise and reproducible treatment process
easy to control the process (only dose/time to be controlled)
shelf life of treated products is long and depends on integrity of packaging
Author: Emmanuel Nii Tackie
Mobile:024 4299229 / 023 3299229
FAO Prevention of post-harvest food losses: fruits, vegetables and root crops – a training manual FAO Training Series 17/2, Rome, 1989
Ghana Atomic Energy Commission (GAEC), Biotechnology and Nuclear Agriculture Research Institute (BNARI) – The Radiation Technology Centre (RTC), Gamma Irradiation Facility (GIF) brochure, 2011
Kader, A. A. (2005) (PDF). Increasing Food Availability by Reducing Postharvest Losses of Fresh Produce UC Davis
Lopez-Camelo, Andres. Manual for the preparation and sale of fruits and vegetables – from farm to market. FAO, Rome 2004
Mrema, C. G. and Rolle, S. R. (2002). Status of the postharvest sector and its contribution to agricultural development and economic growth. 9th JIRCAS International Symposium – Value Addition to Agricultural Product, pp. 13-20.