Stewart Postharvest Review An international journal for reviews in postharvest biology and technology
Modified and controlled atmospheres for tropical fruits Elhadi M Yahia Facultad de Ciencias Naturales, Universidad Autónoma de Querétaro, Campus Juriquilla, Querétaro, 76230, México.
Abstract Purpose of the review: This review provides updated information on the research and application of modified and controlled atmospheres (MA and CA) for tropical crops. Recent findings: The increase in the demand and, thus, in the export of tropical crops, have increased the need to investigate and develop technologies that can maintain the quality and postharvest life of these crops for prolonged periods. MA and CA are adequate technologies that can help to extend the postharvest life of crops. MA and CA are not used for storage of tropical crops, but are used for their marine transport. Very little research has been done on MA/CA of tropical crops as compared with temperate fruits such as apples and pears. Most of the research was done on avocado, banana, mango, papaya and pineapple, while very little has been done on cassava, custard apple, feijoa, guava, lanzone, loquat, rambutan, sapodilla and sugar apple, and no research has been reported on atemoya, birba, breadfruit, cacao, carambola, cashew, coconut, jackfruit, langsat, longan, macadamia, mammee-apple, mamey, mountain apple, tomatillo, pulsan, white sapote, soursop, tamarind and yam. Directions for future research: 1) Potential benefits and ideal MA/CA conditions is still needed for intact and lightly-processed tropical crops, especially those for which little or no information is available. 2) Insecticidal atmospheres, especially in combination with other treatments such as heat, seem to be very promising and should be further investigated for all tropical crops. Information needed include the tolerance of different crops to these atmospheres, mortality of different species of insects, ideal gas composition, temperature, and duration of treatment. 3) The mode of action of MA/CA in alleviating some physiological disorders, especially chilling injury, is still not clearly understood. The mechanism by which some physiological disorders are initiated or augmented by MA/CA is also not yet understood. Research aimed at investigating the cause of and developing methods to control these physiological disorders will improve the application of MA/CA for tropical fruits. 4) The variable results reported for modified atmosphere packaging are due to use of variable conditions (differences in cultivars used, stages of maturity, types of films, sealing methods, sizes of packages, temperatures and relative humidity, etc). Therefore, experiments should be controlled to distinguish effects that are due to atmosphere modification from those due to other factors. 5) The behaviour of fruit after MA/CA is still not fully understood and, therefore, the methods of handling MA/CA-treated crops are not well established. Further research is needed to investigate the metabolic changes caused by MA/CA and, thus, to implement adequate methods of handling. 6) The potential use of low pressure atmosphere (LP) for transport of exotic tropical crops, especially those that are very sensitive to ethylene and do not require the addition of other gases (such as CO2 and CO), should be further investigated. There is a need to develop inexpensive LP technology. 7) More in-depth studies are needed to investigate the potential use of CO in combination with MA/CA, especially during transit. Treatments and methods to permit safer use should be developed. 8) Further and in-depth research on the mode of action of MA/CA are still needed in order to increase the commercial use of the technology for tropical crops. These studies should contribute further to our understanding of the mechanism by which low O2/high CO2 conditions control fruit ripening/senescence or cause tissue injury. Very little is known about protein turnover and gene expression in crops held in MA/CA. Thus, molecular studies are needed to identify clones for genes that are switched on or off in response to low O2/high CO2, in order to identify molecular markers to monitor responses of fruits to MA/CA, and to try to manipulate tissue response. Keywords: Controlled atmospheres; modified atmospheres; tropical; fruits; vegetables; storage; transport; packaging; quarantine Correspondence to: Elhadi M Yahia, Facultad de Ciencias Naturales, Universidad Autónoma de Querétaro, Campus Juriquilla, Querétaro, 76230, México. Tel/Fax: +52-4422281416; email:
[email protected] © 2006 Stewart Postharvest Solutions (UK) Ltd.
Stewart Postharvest Review 2006, 5:6 Published online 01 October 2006 doi: 10.2212/spr.2006.5.6
Yahia / Stewart Postharvest Review 2006, 5:6
Abbreviations 1-MCP 1-Methylcyclopropene Controlled Atmosphere CA Controlled Atmosphere Packaging CAP Chilling Injury CI Ethylene Dibromide EDB Low Oxygen Atmosphere LO Low Pressure (hypobaric) Atmosphere LP Modified Atmosphere MA Modified Atmosphere Packaging MAP Methyl Bromide MB Pressure Swing Adsorption PSA Relative Humidity RH
Introduction Until recently, most tropical crops were only grown in home gardens and small farms primarily for local consumption. Currently, several tropical fruits such as banana, pineapple, papaya and mango are among the most important horticultural crops. The market for tropical fruits has increased significantly in the last 2 decades. This is due to several factors including changes in diet habits, demand for exotic food products, and the use of improved technologies such as storage and transport. The improved prices and technologies, and increased demand are resulting in increased cultivation of a diversity of tropical crops in several regions of the world. Most tropical crops are chilling sensitive and cannot be maintained at low temperatures. As a consequence, most of these crops have a relatively short postharvest life (only few weeks) compared with many temperate and subtropical fruits [1]. Modified (MA) and controlled atmosphere (CA) have been shown to ameliorate chilling sensitivity in several crops, including those of tropical origin [2**]. The tropics are characterised by conditions (high temperature and relative humidity [RH]) that favour the spread of insects and diseases. Some of the most important diseases that affect tropical fruits and cause major losses include anthracnose (caused by Colletotrichum gloeosprioides Penz.) and stem end rot (caused by Diplodia natalensis P. Evans). Anthracnose is the major postharvest problem in avocado, banana, guava, mango and papaya, and contributes to most of their losses [1]. MA/CA can control some decay, either directly or indirectly, by delaying ripening and senescence of the commodity and, thus, maintaining resistance to pathogen attack [2**]. Many insects infect tropical crops. Some of the most important insects include various species of fruit flies such as Ceratitis (found in several regions of the world), several Anastrepha species (found in South and Central America and the West Indies), the genus Dacus (found in Africa and Asia,
etc) [3*]. Quarantine treatments for tropical fruits are needed in order to facilitate their distribution around the world [3*]. Traditionally, chemical fumigants (mainly ethylene dibromide [EDB] and methyl bromide [MB]) have been the principal treatments used for this purpose [3*]. However, EDB was banned in 1984 due to the associated health risks. MB is still being used for some crops, but with restrictions. Several physical quarantine treatments have also been tried [3*]. Low temperatures (0–2.2ºC for 10–16 days) can be used to control the Mediterranean fruit fly. However, these temperatures cannot be used for most tropical fruits because of their chilling sensitivity. Hot water treatments have been used in several countries to control fruit flies in mango (46.1ºC for 65–90 min) and papaya (using a two-stage heating process with temperatures of 42ºC for 30 min and 49ºC for 20 min). Vapour heat treatments have also been developed and used, although injury has been reported in both mango and papaya fruits treated with heat [3*]. Irradiation has proved potentially applicable for insect control in some tropical fruits such as mango and papaya, however, commercial application is still very limited due to several problems including possible injury to the fruit, high costs and consumer concerns. MA and CA (>1.0 kPa O2 or
