The supply of imports

Press, 18 July 1979, Page 14

The supply of imports

Bananas are grown in tropical climates around the world. They are imported to New Zealand from the Pacific islands of Tonga, Rarotonga. and Western Samoa, but the bulk of our bananas come from Ecuador in South America.

There are many varieties of cultivated bananas. botanically related but differing in handling characteristics and disease resistance. The principal banana varieties grown commercially are Gros Michel, Dwarf Cavendish, Giant Cavendish and the Claret or Red banana. Most bananas marketed in

this country are of the Cavendish variety. Giant Cavendish are a • disease-resistant variety and as a dwarf variety are best able to withstand wind and storm damage. The banana plant by nature has a shallow root system and' a large leaf area and relatively low velocity winds will topple a plant to the ground. Bananas do not ripen satisfactorily on the plant in the tropics, therefore the fruit is harvested green and at a stage of development which will allow it to be transported in refrigerated carriers to the country of destination, arriving there still green. Another reason for cutting the bananas green is that the susceptibility of the fruit to handling damage is greatly increased as ripening advances. However, even with green fruit, precautions must be taken to minimise the handling of the tender fruit. The banana stems are harvested and transported to strategically located receiving stations. Here the hands are cut from the stalks and these are then subjected to various processes for the removal of foreign matter, the elimination of latex (elastic milky fluid which exudes from green fruit when cut) and treatment with fungicides. To prevent ripening during shipment, the holds of refrigerated ships are precooled so that the field heat wili be removed as quickly as possible. The fruit is reduced to a low carrying temperature which is maintained throughout the journey to the port of discharge. All

North Island fruit is unloaded at Auckland, then the ship sails south to discharge the South Island supplies at Lyttelton. The discharge of a banana cargo must be a continuous and rapid operation from the time the ship's hatches are first opened until all the fruit is unloaded. The bananas are protected as far as possible from damage caused by exposure to excessively high or low temperatures.

During ripening, enzymatic changes occur in ther pulp of the fruit. The pulp of the green fruit contains about 20 per cent starch. As ripening progresses, this starch is converted to sugars- Colour changes in the peel occur simultaneously with the pulp change and are also enzymatic. The rates at which these changes take place depend upon the relative activities of different enzymes which are in turn stimulated by the physical conditions to which the fruit is exposed. Green bananas contain two pigments —. green clorophyll and yellow carotene. During ripening the chlorophyll is gradually destroyed by enzymatic action, allowing the carotene to become more and more evident.

Within certain limits, the period required for ripening green fruit can be extended or shortened to meet trade requirements. Under average conditions ripening is not accomplished in less than four days. Control factors in banana ripening are general 1 ; recognised to be temperature, humidity and ventilation.