By NAVEED AHMAD, Institute of Horticultural Sciences, University of Agriculture Faisalabad
Pakistan is one of the leading citrus especially mandarins (Kinnow) producing countries of the world. Pakistan annually produces about 200 thousand metric tons of citrus fruit with the major share (70%) of Kinnow. According to the official statistics, Pakistan is the sixth largest Kinnow producing country of the world with plantation of half million acres producing 2.5 million tons of fresh fruit. Kinnow is short season crop starting from December and ends in April. Over this short period of time a huge amount of fresh fruit is produced. The quality of fruit starts deteriorating immediately after harvesting if not properly handled.
Unfortunately there is no proper post harvest handling mechanism as well as marketing system in Pakistan that leads to a large scale post harvest losses (35-40%). Juice processing industry is also not well established in the country rather two concentrate plants established in Sargodha region were closed down in the recent past.This situation has encouraged marketing of the fresh fruit to local as well as international markets, and the world trade in fresh citrus fruits is growing continuously. Export of Kinnow alone contributes about 97 percent in total export of citrus fruit from the country which earns around Rs.7000 million foreign exchange. This figure can be increased significantly by controlling pre- and post-harvest losses. From Far East to Gulf and Europe to America there is a great demand of Pakistani Kinnow. But lack of appropriate pre- and post-harvest management measures, insufficient packing houses, limited cold chain facilities and our conventional marketing system is a big hindrance in the export of fresh citrus fruit to its full potential. Both, the farmers and the government should try to overcome there respective responsibility to increase the export and capture the gaps in the international market. Eastern European countries may emerge a potential markets for Pakistan. Government should try to enter in these countries immediately. Farmers should play their role at their end by producing a crop of international standard. There are some suggestions for the farmers to prepare their produce for export.
1. Pre-Harvest Factors Influencing the Post-Harvest Management:
Once the fruits are harvested, then the overall quality of fresh fruits can hardly be improved. The final market value of the produce depends upon the grower’s ability to apply best available pre-harvest technology and subsequent harvesting and then post-harvest technology. The pre-harvest technology, like use of fertilizers, irrigation, pest control, growth regulators, climatic conditions and tree conditions, influences the fruit potentiality for storage by modifying physiology, chemical composition and morphology of fruits. In pre-harvest treatment, if the spray (10 ppm) of Gibberellic acid is done at colour break stage, it delays colour development, maintain firmness, thereby allows to extend harvesting period. Similarly, the use of potassium fertilizers extends the shelf life of the fruits.
a) Harvest Maturity Indices
In tropical and subtropical countries, the development of the fruit is affected by the temperature. Mandarins are harvested at fully mature stage. The most commonly used indices in the peel colour. Fruits are considered mature and ready for harvest if they have yellow orange colour on 75% or more of the fruit surface. Internal quality signs of harvest maturity include total soluble solids contents (TSS), acidity and TSS/acid ratio of juice. The juice should have TSS of 8.5% or higher which can be determined by a hand held refractometer. Harvesting should begin with the large fruit. Acidity should be 0.3-0.4% with TSS/acid ratio of 6.5 or higher. Smaller fruit, or those which are slow to turn color, should be harvested later on in the season.
b) Time of Harvest
It is best to harvest citrus on a clear, sunny day with low humidity. The fruit should be harvested as soon as the dew has evaporated. On a cloudy day, the fruit should be harvested in the afternoon. Fruit should not be harvested at all on a rainy day.
c) Harvesting Method
To prevent physical damage to the fruit, the worker should trim fingernails, wear gloves, and use special harvesting scissors with rounded ends to cut the fruit. To harvest the fruit, it should be held in one hand, and the other hand used to cut the fruit stem together with a few leaves. Then the fruit is brought close to the chest and the rest of the stem is cut off smoothly, close to the fruit.
The container used for newly harvested fruit should be solid, with good ventilation. Fruit in flexible containers tend to crush each other, causing bruises. The bottom of wood or bamboo containers should be lined with newspapers, a paper bag or a fertilizer sack. It is important to move containers as little as possible, and not to leave them standing in the direct sun light.
2. Treatment after Harvesting:
It is very difficult to harvest fruit without some minor damage. Sometimes a chemical treatment is applied to the fruit before storage, to reduce the incidence of post harvest diseases. Citrus fruit age during storage. The stem becomes first yellow, then brown. Finally, it drops off, leaving a vulnerable place on the fruit which may be infected by fungus diseases. A treatment of 10 to 40 ppm 2,4-D can prevent the fruit stem from drying up and dropping off. The chemical thiabendazole (40% diluted at 500X) can be sprayed onto fruit one or two weeks before harvest. Alternatively, fruit can be soaked for three minutes immediately after harvest. These treatments reduce the incidence of fruit rot during storage.
a) Curing and Washing
During the curing, field heat of the fruit is brought down; this helps in stabilizing the metabolic process. The fruits are spread on the floor in orchard’s yard, having the cushion of paddy straw for nearly 24 hrs and then washed to remove the dirt. By washing the original colour and luster of the fruits is also recovered.
b) Peel De-Greening
Mandarins can be treated with ethylene which is a naturally produced plant growth hormone effective as a de-greening agent to de-green the skin to improve the external skin colour which is very important for export market. Ethylene treatment breaks down the green chlorophyll pigment in the exterior part of the peel and allows the yellow or orange carotenoid pigments to be expressed. This treatment is solely cosmetic in effect and does not alter the flavor of the fruit.
c) Grading of Fruits
Grading is one of the most important procedures to be followed in post harvest handling, as it determines the quality, shelf life and price of the fruit. During grading, the produce is sorted according to the fixed grade standard, taking into consideration various quality factors to make a homogenous lot. Grades of citrus fruits are based on soundness, firmness, cleanliness, size, weight, colour, shape and freedom from foreign matter, disease scars, insect damage and mechanical injury. Grading and sizing of fruits can be done manually or mechanically. Fruit of different sizes should not be mixed together. Generally, large fruit fetch the highest price. However, for export purpose grading should be done according the standards of the targeted market.
The application of food grade wax, kaolin or similar coating, should be used to enhance the appearance and minimize water loss. In addition, to prevent the fungal growth, proper fungicide in prescribed quantity should also be used while giving wax treatment. The post packing treatment like fumigation and gamma-ray irradiation can be used for high priced fruits.
3. Packaging and Storage:
The packaging of fruits is required for efficient handling and marketing, better eye appeal and better shelf life by reducing mechanical damage and water loss. The proper packaging protects the fruits from pilferage, dirt, physiological and pathological deterioration during further handling. Efficient packaging of produce in uniform size reduces the need for repeated weighing and can facilitate handling, stacking, loading, unloading, better storage, long transportation, transshipment and marketing. Corrugated fiber board boxes should be used for export purpose. Paper of plastic films is often used for lining of packing boxes in order to reduce transportation loss and prevent friction damage. The size, type and capacity of the box and number of layers and count of fruits kept in the packages, material used as packaging cushion may vary according to the requirement of the importing country.
Boxes should be stacked inside the storage room in a way that maintains good ventilation. If storage is to be done for some time, in the first few weeks of storage, ventilation windows should be left open. Throughout the storage period, the windows should be left open at night or in cold weather, in order to cool the fruit.
Fruits boxes should be transported in refrigerated vehicles from farm store/cold store to the shipment areas (air port or sea port). During transportation and shipment boxes should be handled carefully to avoid bruising injuries. On arrival in the importing country fruit should be transported in a cool chain system.