Modified and controlled atmospheres for tropical fruits

Abstract

Purpose of the review: Th is review provides updated information on the research and application of modified and controlled atmosph eres (MA and CA) for tropical crops. Re cent findings: Th e increase in the demand and, thus, in the export of tropic al crops, have increased the need to investigate and dev elop technologies that can maintain the quality and postharvest li fe of these crops for prolonged periods. MA and CA are adequat e techno logies that can help to extend the postharvest life of crops. MA and CA are not used for storage of tropical crops, but are u sed for t heir marine transport. Very little research has been done on MA/CA of t rop ical crops as compared with temperate fruits such as appl es and pears. Most of the research was done on avocado, banana, m ango, papaya and pineapple, while very little has been done on cassava, cust ard apple, feijoa, guava, lanzone, l oquat, rambutan, sapodilla and sugar appl e, and no research has been reported on atem oya, birba, breadfruit, cacao, carambola, cashew, coconut , jackfruit, langsat, longan, m acadamia, mammee-apple, mamey, mount ain apple, tomatillo, pulsan, white sapote, soursop, tamarind and yam. D irections for future research: 1) Pot ential benefits and ideal MA/CA conditions i s still needed for intact and lightly-processed t ropical crops, especially t hose for which little or no inform ation is available. 2) Insecticidal atm ospheres, especially in com bination wi th other treatments such as heat, seem t o be very promising and should be further investigated for all tropical crops. Informati on needed i nclude the tolerance of different crops to these atmospheres, mortality of different species of insects, ideal gas compositi on, t emperature, and duration of treatment. 3) The mode of action of M A/CA in alleviating some physiological disorders, especially chilli ng injury, is still not clearly understood. The mechanism by whi ch some physiological disorders are initiated or augmented by M A/CA is also not yet understood. Research aimed at investigating t he cause of and developing methods to control these physiologi cal disorders will improve the application of MA/CA for tropical fruit s. 4) The variable results reported for modified atmosphere packag ing are due to use of variable conditions (differences in cu ltivars used, stages of maturity, types of films, sealing methods, sizes of packag es, temperatures and relative humidity, etc). Therefore, experiments should be controlled to distinguish effects t hat are due t o atmosphere modification from those due to other factors. 5) The b ehaviour of fruit after MA/CA is still not fully underst ood and, t herefore, the methods of handling MA/CA-treated crops are not well established. Further research is needed to investigate th e m etabolic changes caused by MA/CA and, thus, to implement adequate methods of handling. 6) The potential use of low pressure atm osphere (LP) for transport of exo tic trop ical crops, especially those that are very sensitive to ethylene and do not require th e additi on of other gases (such as CO2 and CO), should be further investigated. There is a need t o 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. Treatm ents and methods to permit safer use should be developed. 8) Furt her and in-depth research on the mode of action of MA/CA are still needed in order to increase the co mmercial use of the technology for tropical crops. These studies should contribute furth er to our underst anding of the mechanism by which low O2/high CO2 conditions control fruit ripening/sen escence or cause tissue injury. Very little is known about protein turnover and gene expression i n crops held in MA/CA. Thus, m olecular studies are needed to identi fy 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 fr uits to MA/CA, and to t ry to manipulate tissue response. Ke ywords: C ontrolled atmospheres; modified atmospheres; tropical; fruits; vegetables; storage; transport; packaging; quarantine