Long-Distance Controlled Atmosphere Transport of Avocados
FFTRI, Private Bag X5013, Stellenbosch
Abstract. Low temperature storage is essential for long-distance transport of avocados but results in chilling injury if the temperature is too low and physiological disorders and waste, if a the temperature is too high. Controlled atmosphere (CA) storage can extend storage life, maintain quality, drastically reduce chilling injury and allow storage at lower temperatures.
Controlled Atmosphere Applications
The relative humidity in the storage atmosphere should preferably be in the 90% to 95% range because it was found that moisture loss may increase chilling injury (Bower and Cutting, 1987). The avocado being a climacteric fruit should be stored and transported at very low ethylene levels in the atmosphere to reduce early softening. Efficient ethylene removal systems are, however, still under development (Heap, 1989).
Reason for CA storage. The following advantages can be obtained with CA storage of South African grown avocados (Eksteen and Truter, 1983):
1. Storage and shelf life can be increased considerably;
2. Chilling injury can be drastically reduced; and
3. Physiological disorders such as vascular abnormalities and mesocarp discoloration can be reduced to an absolute minimum.
Practical Application. CA storage must be cost-effective and must result in less quality losses and increased storage and shelf life. It must also be practical, easy and safe to apply and must not require very sophisticated expensive equipment.
These above mentioned benefits were applied
in practice when 'Hass' avocados were shipped from
With an 8-day shipping schedule (16- to
19-day voyage), from
Extension of storage life without quality
loss may, however, be to the advantage of production areas or countries
situated close to the market (e.g.
CA storage and distribution systems. CA cold stores have little practical benefit in a long distance marketing system except that it may be utilized to extend storage life. In such a situation, the fruit can be CA-stored prior to regular atmosphere (RA) air freight to a distant market or to shipping under CA (longer distances) or RA (shorter distances). In this case, it is of absolute importance to apply the CA treatment as soon as possible after harvest.
CA containers combine the CA concept with a
practical and economical transport system. It has been proven (McGlasson, 1989) that avocados can be shipped successfully
for six weeks (
Cost and reliability of the container, shipping and transport cost and an effective supporting infrastructure are factors to be considered before venturing into long distance transport of avocados in CA containers.
CA vessels or decks. CA decks or chambers on ships can be regarded as
floating CA cold stores. The same results can be expected as with CA stores if
the storage conditions are kept optimum. One of the major problems, however, is
to maintain a gas-tight seal in a structure with relative movement between
different components. For best results, CA must be applied soon after harvest.
This may be a problem in countries such as
Another aspect that needs very careful consideration is that big volumes have to be shipped to make the operation economically viable. Such large volumes may not be readily available within a few days or may create marketing problems where large volumes have to be sold within a limited period. CA-shipments may, however, combine the benefits of CA storage with a relatively low cost transport system. This can make long distance transport very feasible in supplying a sophisticated market with good quality fruit.
Modified Atmosphere Applications
Modified atmosphere (MA) conditions are achieved by enclosing the fruit in a polyethylene bag or wrapping it in a permeable film or container. Various gas pre-treatments can also, for the purpose of this discussion, be regarded as MA storage. These systems, however, may not always have the same or consistent end results when compared to CA. Reasons for this are that the optimum conditions cannot always be maintained at desired levels for prolonged periods. Another problem is that the normal atmosphere must be restored after a certain period of pre-treatment or prior to ripening.
MA Packaging. Avocado fruit individually packed in polyethylene or
cellophane bags were previously exported from
Pre-conditioning atmospheres. Avocado fruit respond very well to treatment with 20%
to 25% carbon dioxide immediately after harvest. Best results are obtained with
a 48 to 72 hour exposure to these conditions at 5.5C. The physiological effects
on the enzyme systems (
Possible Handling And Long-Distance Transport Systems
The application of CA in any transport system is dictated by many factors of which economical considerations, logistics and availability of suitable equipment are only a few. The transport chain may be divided into three distinct areas; i.e. packhouse cold store to port of export, port of export to port of import, and port of import to market.
On land CA store followed by CA container road and/or sea transport or CA deck shipping. This concept may be less feasible because of no or little off-season utilization of cold store and loss of valuable storage/transport time to distant markets. On land CA storage, however, allows for immediate preconditioning of fruit prior to MA or RA shipping where CA shipping is not available.
Door to door CA container followed by CA container road and/or sea transport or CA storage post shipping. This concept may be the ideal because it allows for immediate and continuous CA shipping. Cost and logistics are, however, important considerations especially where the production area is far from the port and if CA containers are not readily available.
Immediate CA shipping. This can be done by either port-to-port CA shipping
or CA storage post-shipping. This concept can be utilized if CA conditions can
be applied very soon after picking. The production area must be close to the
port and CA vessels must be scheduled to avoid delays.
Gas pre-conditioning of the fruit followed bv CA container or CA deck shipping or RA road and/or sea transport. This concept may be more practical, economical and quality effective and can be done at the packhouse or during road transport to the port. It does not require expensive equipment and can combine immediate pre-conditioning followed by RA shipping.
MA packaging followed by RA storage and transport only. MA packaging should never be combined with CA because of the restriction of gas movement caused by the MA film or membrane. Although it allows for longer storage and long distance transport, the MA film should be removed prior to marketing to avoid fermentation and to trigger ripening.
RA shipping with either gas preconditioning or MA packaging. Actual RA shipping period should not exceed 21 days unless the fruit is preconditioned or some sort of MA is applied. Both treatments have a limited effect and are not really designed for long distance transport and marketing.
A controlled atmosphere environment for long distance transport should only be considered if it is economically and practically feasible. CA vessels can only be used for port to port transport and decks must be filled rapidly requiring fast packing of big volumes. The latter may create marketing pressure. CA containers make a door to door concept possible and allow for much more flexibility in picking, shipping and marketing. Pre-treatment with various gasses with or without MA procedures do not really extend storage life of avocados, but may result in less quality loss during transport and marketing. CA pre- or post-shipping storages do not contribute towards long distance transport, but may extend the marketing season.
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