BEING one of the most important tropical fruit crops of the world, mango is called King of Fruits. Its different varieties are very popular due to attractive fruit peel colours, specific fragrance, delicious taste and nutritive value.
Its fruit contains 10-20 per cent sugar and ample quantity of vitamin ‘A’ and ‘C’ with small quantity of vitamin B. Climatic conditions of Pakistan are very favourable for good production of mango and it currently ranks 5th in the world in term of total fruit production. However, we are not getting good share in international trade due to some problems including quarantine restrictions by different countries.
Having short shelf life, most of mango varieties cannot be stored at low temperature (below 13°C) and it becomes very difficult to export this fruit to international markets. Importing countries like China and Iran have become very sensitive regarding quarantine requirements against insect/pests and diseases specially fruit fly. Both of the countries had demanded hot water treated mangoes to get rid of fruit flies. Since long time, scientists have been working on this aspect using different techniques with an objective to meet quarantine requirements.
Formerly, methyl bromide gas was used in fumigation but its use was abandoned due to higher residual effects unsafe for human health and negative effects on fruit quality. So the researchers concentrated on a technology safe for human health and environment with least negative effect on fruit quality. Use of heated water has been found to be more safe and effective in meeting the quarantine requirements. It may be used in two ways i.e hot water treatment and vapour heat treatment (water is passed over fruits in the form of heated vapours). Comparatively, hot water treatment is relatively a cheaper method and it is better for developing countries like Pakistan to use this method.
Hot water treatment: Fruit is immersed in hot water for a specific time and temperature of water is maintained at a specific level. Duration of fruit immersion and water treatment is decided according to the target (disease or insect/pest). For example, hot water treatment trials conducted in different countries has revealed that control of anthracnose needs five minutes dipping in hot water at 52°C whereas to kill fruit fly larvae within pulp, it is better to apply hot water treatment at 45 - 48°C for 60 - 75minutes.
In 1984, USA approved this technology for quarantine control of insect/pests and diseases. According to WTO agreement, any exporting country will have to meet all such post-harvest treatments for quarantine control, imposed by importing country. After USA, several other mango importing countries like China, Iran and Japan demand hot water treated mango to control problems of quarantine concerns. Thus the spread of, further infestation and infection can be controlled in countries where these do not exist.
Keeping in view the importance of this technology, many exporting countries have developed their treatment protocols for their local varieties. These countries include USA, Philippines, Australia, India, Thailand and Haiti etc. Now, Pakistan is also facing quarantine issues for export of mango fruits. For example, protocols signed with Iran (45°C – 75minutes) and China (48°C – 60minutes) for export of mango requires hot water treatment.
Hot water treatment technology not only makes fruit free from insect/pests and disease but the method is also cheaper. During the treatment, it is necessary to keep temperature of water at specific level. As fruit peel may be injured due to direct contact with hot water, so it is also important to regularly monitor fruit pulp temperature.
In Pakistan., information regarding hot water treatments was not available and it was necessary to find out a protocol for different varieties for their successful export. Recently, Institute of Horticultural Sciences, University of Agriculture (Faisalabad) with collaboration of Pakistan Horticulture Development and Export Board (PHDEB) have conducted research trials on this aspect and tried to make mango fruits free from fruit fly.
In these trials, mango fruit were tested against hot water treatment protocols given by China (46°C – 60minutes) and Iran (45° C – 75minutes). Research trials were conducted on. Sindhri which is a promising and an export quality mango variety. It was found that by the proper use of this technology, we can also meet the import requirements of various countries and earn higher prices in international market.
The following points must also be kept in mind during the use of hot water treatment technology:.
i. During harvesting, fruit should be mature because immature fruits are more susceptible to the development of skin injuries after hot water treatment.
ii. During handling and transit, treated fruits should be protected from physical injury because such injuries become more prominent on hot water treated fruits.
iii. If mango fruits have been taken from storage, it is better to keep them for some time at ambient condition before applying hot water treatment until and unless fruit temperature reaches room temperature (24±1°C). After treatment, again fruit should be kept at ambient condition to lower down fruit temperature to room temperature, after which they can be pre-cooled for further storage and transportation to target importing country by air or through sea. So far, only three certified processing plants in Karachi have been certified for hot water treatment . There is need for more.