By Muhammad Iqbal
|Currently working as Chief Operating Officer Pakistan Horticulture Development & Export Board, He has served the Federal Government in different positions starting from mid management to senior management for 30 years. Prior to current position, he was serving FAO. He has attended a number of national and international workshops, seminars and expert consultations and has authored over 70 technical/research publications.|
Post – Harvest Handling System
Mangoes can be successfully stored for up to three weeks if the recommended harvest maturity, post harvest handling and storage conditions are employed.
All mangoes to be exported by air should be harvested in the physiologically mature, hard, green condition. Harvest maturity in most varieties is judged by the position of the shoulders in relation to the position of the stem as illustrated thru
Figure 1: There is no sure way to know when mangoes are ready for harvest. One of many methods is this: in immature fruit, the shoulders are below the level of attachment of the stem (a); in mature fruit, the shoulders have risen above the stem-attachment level (b). This method does not apply to all the cultivars and must be considered with other factors
Half mature fruits may be included in the shipment, but should not make up more than 25% of the total. Fruit harvested in ripe condition or with more than 15% yellow coloration, should be selected in the field and not included in export shipments. Ripe fruits are highly susceptible to bruising and mechanical damage during handling and transport. Immature fruits should not be shipped.For mangoes exported by sea, the optimum stage of harvest maturity is the “half mature” stage. Fruits should not show any signs of softening or de-greening yellow colour development. Immature fruits shout not be shipped.
Assessment of Harvest Maturity in Mangoes
The following descriptions are appropriate for Sindhri & Chaunsa and for other varieties which show similar morphological characteristics.
• Fully mature: outgrown shoulders, formation of a depression with ridges at the stem end, firm and green;
• Half-mature: shoulders in line with the slightly ridged edges, firm and green;
• Immature: shoulders below the stem insertion with ridges absent, firm and green.
The maturity can also be determined by putting the fruit in 2% salt solution. Those that sink are considered mature while those that float are considered immature.
Where possible, mangoes should be harvested by hand from the ground, by snapping the mangoes from the stem. Fully mature fruit will detach easily, whereas half-mature fruit will not. Optimum harvesting involves using secateurs and cutting the stem 2 – 3 cm away from the fruit, and the latex allowed to drain (this technique reduces latex exudation and staining and reduces the possibility of entrance of fungal organisms). Later the stem should be further trimmed with a sterilized knife (dipping in a solution of calcium hypochlorite) to 0.5 or 0.3 cm as demanded by the importer. Where harvesting by hand from the ground is not possible, harvesting implements should be used. The most suitable involves a long pole with a cutting blade and a small bag under the blade to catch the fruit
Figure 2: Picking poles are used to harvest mangoes which cannot be reached from the ground or ladder. Both the factory-made (a) and home-made (b) types have cutting device and a catching bag
Alternatively, climbers may use cotton bags which are filled and lowered to the floor.
Mangoes should never be knocked from the tree, dropped or thrown to the ground. Least option will be that climber throws fruit which is held on sack and then gently released to the floor (Figure 3).
Mango-picker in the tree drops the fruit, and catcher breaks its fall using a jute sack supported by his hands and one foot. He then lowers the bag to ground level and the mango rolls out without damage
The out-grading should be carried out in the field to remove immature,
undersized, damaged, bruised, scald or ripe fruit. The fruit on any one tree are of different ages because flowering and pollination occurs over a period of several weeks. Therefore, all the fruits do not mature simultaneously. Fruits are usually harvested from individual trees on several occasions throughout the season.
After harvesting, latex should be allowed to drain away from the fruit and the fruit placed in plastic field crates. Bags, sacks and buckets are to be avoided as these generally result in mechanical damage and bruising. Harvested mangoes should not be left in direct sunlight, wind or rain, either in the field or during transport from the field to the packing facility.
Field Heat Removal
The field heat of the fruit should be removed soon after harvesting. It is essential for improved shelf life of mangoes. Different methods can be applied for removing field heat. These include air cooling, hydro-cooling, vacuum cooling and forced air cooling. However, in our situation hydro cooling is most appropriate and practical method. The fruit should be immersed in ice cold water in field crates or in bulk. The use of shower-type hydro cooler will be more appropriate. Addition of sodium hyperchlorite (100 ppm) in water will help in removing debris and latex stains.
Grading and Packing
On arrival in the packing area, the mangoes should be graded for removal of immature, under-sized, damaged, blemished, bruised, infested or ripe fruit. Fruits should be graded in each carton according to the variety, size (giving a range of counts for each shipment) and maturity (firm green full-mature and half-mature fruits will ripen at different rates and should not be packed in the same carton).
When packing, fruits should be placed leaning to the side rather then directly on the base. Mangoes should be packed in single layer one – or two – piece fully telescopic, self-locking fiberboard cartons (bursting strength requirements 250-275 lb/in2). Ventilation and handle holes are recommended to provide adequate ventilation and ease of handling. Cartons labeling requirements for the individual markets should be followed. A layer of shredded paper in the base of the carton is recommended, as this will assist in cushioning the fruit. Each alternate mango in a carton should be wrapped in a tissue to reduce fruit to fruit rubbing; small identity labels attached to alternate fruit will assist in product presentation. Net weight requirements are 2, 3, 4, 5 & 7 kg depending on the market destination. Cartons must not be over-filled during packing.
Palletisation is essential to minimize fruit damage due to multiple handling. Movement of fruit within pack-houses or during temporary storage can be aided by palletisation. For sea-shipment exports of mangoes, palletisation is a necessity.
If mangoes are to be exported to the destination within two to three days of harvesting, as with air-shipments, then pre-cooling is advisable but not essential. Mangoes transported by sea should be pre-cooled prior to loading into containers or holds. Several methods of pre-cooling are available, and the system adopted should suit the specific requirements and capabilities. Temperature controlled rooms are the most simple, although cooling may be slow if stacking and spacing are not adequate to allow free and even air flow or if the refrigeration capacity is low. A forced air system is more efficient, although this requires a specially designed unit and compatible packaging. Mangoes should be cooled to a minimum of 120C.
Ripening and Storage
For export of mangoes by air, storage ripening may be required prior to shipment. Recommendations for the optimum temperature for ripening of mangoes vary according to the variety and growing conditions although the range of 200 to 250C is usually considered optimum. Temperatures above 250 to 300C may result in ripe fruit with off-flavours and mottling of the peel. Initiation and synchronization of ripening period of mangoes can be achieved with exposure to ethylene gas, whether direct from cylinders or as liberated from ethephon when utilized with a catalytic generator. Acetylene gas liberated from calcium carbide exhibits similar effect. Treatments with gases are carried out in air-tight room from 24 hours at 200 to 250C, 90 to 95% relative humidity. Concentrations of gas required during exposure are 10 -100 ppm (0.001 – 0.01%) for ethylene and 1000 ppm (0.1%) for acetylene. Concentrations of gases are controlled by adjusting flow deliveries or the volume of ethylene delivery liquids (such as ethephon). Air-tight rooms should have adequate air circulation to enable uniform distribution of gas throughout the room. Build-up of carbon dioxide is to be avoided as this reduces the effect of the ethylene and will have a detrimental effect on fruit ripening.
Prolonged storage of more than three to five days should not be used for air-freighted fruit. Prolonged storage should be used in the case of sea-freighted mangoes. At storage temperatures below 120C unripe mangoes will develop chilling injury, which will lead to a drastic reduction in fruit quality and increased spoilage. Storage at 120C with 85-95% relative humidity will maintain the fruit in an acceptable condition, and which will ripen satisfactorily on transfer to higher temperatures. These criteria depend on the variety, harvest maturity and the time of harvest in the season. Fully mature fruits have been found to show a reduced storability when compared to half-mature fruits, and this factor becomes more important as the season progresses. Strict levels of quality control in low temperature stored fruit are essential, as blemishes, bruises, damage and infections will manifest to a greater degree than when exported by air and marketed rapidly. The potential exists in stored fruit for high levels of spoilage and poor quality.
For air-shipmen, it is preferable, although not essential, that transport occurs on aircraft pallets rather than in containers. Shipment in aircraft containers may result in build-up of heat and ethylene which will accentuate ripening. For sea shipments, efficient reefer containers should be used in preference to break bulk system in the hold. Stacking system should allow for sufficient ventilation to assist in temperature maintenance.
Potential Post Harvest Losses
• Mechanical Damage
Mechanically damaged fruit will normally deteriorate rapidly and should not be exported. Damaged regions are susceptible to microbial infection, particularly when low temperature long-term storage is used. Careful handling should therefore be used during harvesting and handling operations such as grading, packing and transportation.
• Low Temperature
Storage at temperature below 120C will result in chilling injury, the symptoms of which include inhibition of ripening, pitting, internal discoloration, prey scald like discoloration of the skin, increased water loss, increased susceptibility to decay and detrimental changes in flavour.
• Pathological Factors
Infection by micro-organisms is generally the most serious cause of post-harvest losses in mango. Disease incidence can be reduced by good orchard management, pre-harvest cultural practices, appropriate handling and post-harvest treatment procedures. Washing in static water tanks will increase disease incidence due to the increase in inoculums from infected fruit, therefore, water has to be changed frequently and contain sodium hypochlorite (100 ppm) and/or suitable fungicide. Post-harvest applications of specific fungicides will assist in disease control.
The important diseases and pests of mangoes include the following:
o Anthracnose (Colletotrtchum gloeosporfofdes) infection occurs in the leaves, stem, young flowers and fruits. In the first three, infection results in depressed black circular or angular lesions; these enlarge and coalesce and affect large areas. Infections of the fruit are usually latent and manifest only as the fruit begins to ripen. Anthracnose is characterized in ripening fruit by small black circular lesions which gradually enlarge and coalesce as the fruit continues ripening.
Mangoes harvested from areas or trees which are known to suffer from anthracnose or for fruit destined for long term storage, treatment is required in hot water bath (550C for 5 minutes) containing 0.05% Thiabendazole. This technique shows good control of anthracnose, but generally requires the use of specialized equipment, as temperature control of the water bath is essential for the effectiveness and prevention of fruits damage. After fungicide treatment, the fruit should be allowed to cool and dry for preparation for grading and packing.
o Stem end rot (Diplodfa natalensts) is particularly apparent during low temperature storage. Infection is characterized by light grey-brown areas in the stem region. Infection is believed to occur through the cut stem. Disease incidence can be reduced by leaving 1 cm of stem attached to the fruit.
o Rhizopus rot (Rhizopus oryzae) develops rapidly at 250C and is characterized by skin splitting and development of course white mould with black spore heads. Infection takes place after harvest, usually through mechanical injury. The incidence can be minimized by careful handling, hygienic conditions and rapid cooling.
o Jelly Seed is usually found only when the fruit is sliced; affected fruit show watery translucent tissue around the stone towards the stem-end which then spreads. The condition is found in harvested fruit but develops as the fruit ripens. The only means of control at present is early harvesting, but this may result in the export of immature fruits.
o Fruit Flies are among the serious quarantine pests and therefore restrictions are imposed on mangoes imports by many countries including China, Iran and Japan. Ideally there have to be less pest prevalence areas combined with recommended post-harvest treatments to satisfy the importers. The integrated pest management technique of controlling fruit flies is world wide accepted and preferred mode. Hence this needs to be widely adopted. Regarding post-harvest treatments, the fruit has to be treated by hot water dip, vapour heat treatment or irradiation. The facilities for hot water dip are limited while those of vapour heat treatment and irradiation at experimental scale only. The development of these facilities on commercial scale is needed.
Post Harvest Handling of Mangoes
Market requirements state that mangoes on arrival should be:
• Physiologically mature;
• Commencing ripening with 30 to 50% coloration;
• Significant area of golden colour on the fruit shoulders;
• Relatively firm;
• Minimum sugar content of 10%;
• Uniform shapes;
• Free from disease, decay, sunscald, cracks, bruises, latex stains, insect and mechanical damage; and
• Conform to the weight and size specifications.
Volume sales of mangoes are based on presence of the golden colour, acceptable size of ripeness for consumption, uniform size grading, uniform stage of ripeness and the absence of disease or damage.
Pakistan Horticulture Development & Export Board.