Postharvest practices and technologies to preserve freshness of harvested passion fruits

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By JANE AMBUKO

January 20, 2017, Nairobi. Passion fruit is one of the major fruits produced in Kenya for domestic and export markets. It is the third most popular fruit after avocado and mango. In Kenya, both the purple and yellow varieties are popular depending on the target market or use. Like other fresh fruits, high postharvest losses (> 50%) are reported in passion fruit. The high postharvest losses are attributed to many factors starting from the harvest stage.

The desirable eating qualities of the passion fruits can only be realized when the fruits are harvested at the right maturity. However, due to the high demand for passion fruits in the local and export market, farmers practice ‘strip harvesting’ where fruits of mixed maturities are all harvested in one operation to meet the targeted volume.

It should be noted that the sweetness increases while acidity decreases as the fruit mature and ripen. Therefore mixing fruits of different maturity results in juices of inconsistent quality which affects consumer acceptance. Fruits for fresh market may be sorted into batches of uniform maturity.

Temperature management is critical is postharvest handling of all perishable commodities. Although conventional cold rooms are out of reach for the smallholder farmers involved in passion fruit production, good postharvest handling practices can be adopted to maintain cool temperatures around the produce.

This include harvesting during the cooler times of the day (late evening or early morning); keeping the harvested produce under shade and transporting during cooler times of the day or at night. Additionally there are low-cost cold storage technologies such as zero energy cool chamber (ZECC) = zero energy brick cooler (ZEBC); charcoal cooler; solar cooler and Coolbot™ cold room which are currently being promoted for adoption by smallholder farmers who cannot afford conventional cold rooms.

Passion fruits produce very high levels of ethylene – the ripening hormone. It is for this reason that passion fruit is often used in ripening chambers. The presence of ethylene in storage areas hastens ripening and deterioration of the fruits. Therefore ethylene management – removal or exclusion from the storage areas is critical for quality preservation.

There are various technologies that are used by large scale operators to manage ethylene in storage areas. These include; application of 1-Methylcyclopropene (1-MCP) which is an ethylene inhibitor; use of ethylene scrubbers such as potassium permanganate which oxidises ethylene in the storage area; ozone is also used to oxidize ethylene.

One very simple yet effective postharvest technology that can be used to preserve freshness in passion fruit is modified atmosphere packaging (MAP). When a package that is suitable for the fruit is used, the shelf life of passion fruits can be preserved for up to 15 days (at room temperature) compared to the fruits that are unpackaged. MAP creates an altered atmosphere around the fruit which in turn slows down processes such as respiration, ethylene production and water loss. When packaged in MAP, the package creates a barrier that hinders diffusion of water to the surrounding environment. As a result a saturated environment with high humidity is created around the fruits.

This in turn slows down water loss and subsequent shrivelling of the fruits. Additionally the package creates a barrier to oxygen from the surrounding environment thereby reducing oxygen in the package. Since the fruit is ‘living’ and therefore continues to ‘breathe’, it produces carbon dioxide and uses up oxygen in the package. As a result the oxygen in the package reduces as the carbon dioxide increases. In essence this is what is referred to as modified atmosphere.

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