Enhancement of 'Hass' avocado shelf life using ultra-low temperature shipping or 1-MCP treatment and cold chain management.
Avocados are becoming an increasingly important crop in South Africa, where the main producing areas include Limpopo, Mpumalanga and KwaZulu-Natal provinces. The South African avocado industry faces considerable challenges including increasing competition exporting avocados, particularly to the European market. The processes involved to export avocados has markedly improved over the past two decades, however there is always room for improvement and it is necessary to remain competitive on a global scale. Issues such as fruit being partially soft on arrival, quality defects and cold chain management breakdown are still present. It is necessary to investigate new aspects of cold storage such as extending the storage period and understanding the physiological aspects involved. To improvement such issues, an investigation was conducted on ultra-low temperature shipping (1°C) as well as the use of 1-MCP; the implementation of deliberate cold chain breaks to achieve a better understanding as to the quality influences involved; an extended storage period of 56 days to assess the quality issues and benefits involved; as well as investigating the physiological aspects involved with all above treatments on 'Hass' avocados. An initial study saw early-, mid- and late-season 'Hass' avocados stored at 1°C or 5.5°C for 28 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. Storage at 1°C was comparable with 1-MCP treatment for both fruit softening in storage and extending the ripening period. Storage at 5.5°C resulted in partial in-transit ripening, if 1-MCP was not used. Early-season fruit incurred the most external chilling injury but overall levels were minimal and not concerning. Mid-season fruit were the most sound in terms of quality. It is suggested that 1°C can be used as a viable economic alternative to 1-MCP for long distance shipping of 'Hass' up to 28 days. The cold chain break trial included a 24 hour delay before cold storage, a deliberate 8 hour break at day 14 of cold storage where fruit were removed from cold storage and a control of 28 days cold storage where no break was involved. Early-, mid- and late-season 'Hass' avocados were stored at 1°C or 5.5°C for 28 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. It was found that cold chain breaks do influence the amount of water loss, fruit softening and days taken to ripen. Storage at 1°C did not entirely negate the effects of cold chain breaks compared with 5.5°C, but did result in fruit which were harder at the end of storage and took longer to ripen. The use of 1-MCP also had advantageous effects with respect to significantly lengthening the ripening period, even when a cold chain break occurred, compared with fruit not treated with 1-MCP. As results of the study differed in some respects to those of previous studies, it is recommended that further work be conducted to determine what fruit or pre-harvest factors affect the fruit physiological changes which take place when cold chain breaks occur. Having the option to make use of an extended storage period would be of benefit to the industry if delays occur and fruit have to be maintained under cold storage. Extended storage of South African avocados, especially at the end of the season would also allow for the option of strategically holding back fruit from the export market in order to extend the supply period. It would not only benefit export options, but would also be highly beneficial to local pre-packers, as it would reduce the need to import fruit from the Northern hemisphere production areas during the South African off-season. Early-, mid- and late-season 'Hass' avocados were stored at 1°C or 5.5°C for 56 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. The combination of 1°C with the use of 1-MCP resulted in a good shelf life as well as maintenance of internal quality and integrity. External chilling injury is of concern for early-season fruit, however, mid- and late-season fruit did not incur extensive damage. It is, therefore, advised that fruit placed in extended storage are marketed through the 'Ready ripe' program to mask any chilling injury on the 'Hass' fruit. Avocados are renown as a "healthy food" due to their nutritional value as well as containing relatively high concentrations of antioxidants. The fruit also contain high amounts of C7 sugars which can act as antioxidants. Additionally, C7 sugars and other antioxidants play important roles in fruit quality. Therefore, it is important to understand how varying storage conditions and treatments affect the levels of these physiological parameters. Treatments of cold chain break/delay included a deliberate 8 hour break at day 14 of cold storage where fruit were removed from cold storage, a 24 hour delay before cold storage and a control of 28 days where no break was involved. A 56 day extended storage period was also used. Early-, mid- and late-season 'Hass' avocados were stored at 1°C or 5.5°C for 28 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. The use of 1-MCP maintained higher levels of antioxidants, ascorbic acid and C7 sugars for both the 28 day and the 56 day storage periods. The 24 hour delay had a tendency to increase consumption of anti-oxidant and sugar reserves. The use of 1°C resulted in antioxidant and ascorbic acid levels decreasing while maintaining higher sugar levels. Overall, high stress imposed on fruit decreased reserves resulting in poor quality fruit. The use of 1°C and 1-MCP treatments maintained fruit quality.
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