Various storage techniques of plums and avocados

[摘要] ENGLISH ABSTRACT:Historically the storage of South African plum fruit involved cold storage at singlelow temperatures (-O.5°C). The ever present problem of internal breakdown,however, led to the development of the dual temperature storage regime (a type ofintermittent warming) which was found to restrict the level of internal breakdown.However, this temperature regime led to the development of or unmasking of gelbreakdown (GB).During season one it was proposed that 'Songold' and 'Angeleno' plums could bestored at a single high temperature (7.5°C) during the shipping period (18 days) incombination with controlled atmospheres (CA). This was compared to thecommercially used dual temperature regime (10 days at -O.5°C and eight days at7.5°C). During season two the temperature regimes were adjusted to mirror thestorage of the fruit from the date of harvest until the fruit is purchased. During theshipping period the dual temperature regime and the single high temperature regimewere still compared. It was hypothesised that the fruit could be stored at the highertemperature in combination with CA during shipping, and this would allow theripening of the fruit to be retarded, retaining good quality without exposure to the low,chilling inducing temperatures associated with the dual temperature regime.The storage of both plum cultivars at the single high temperature in combination withCA had a positive influence on delaying the ripening of the fruit. Most noticeablewas the delay of fruit softening and the restriction of colour and GB development ofthe 'Songold' plums. Most importantly, these results were achieved without the fruitbeing exposed to the low, injurious temperatures associated with the dual temperatureregime. It was, however, concluded that due to the suppressed climacteric trait ofthese plums more benefit could be gained from the higher temperature storage incombination with CA on climacteric plums which display stronger ripening patterns.In contrast to the plum industry, the use of CA in the storage of avocado fruit hasrisen to about 95% of the exported fruit. CA storage of avocados has shown positiveresults in retaining fruit firmness, restricting disorder development and extending theshelf life. Recently, research with l-methylcyclopropene (l-MCP) storage ofavocados has been found to be as successful as CA storage and there is a belief that itwill be the answer to storage for the avocado industry once registered for commercialuse.During the first experiment, 'Fuerte' and 'Hass' avocados were treated with CO2shocks (C02 levels which greatly exceed the initial intercellular concentrations of CO2are known as CO2 shock treatments). These shock treatments were done over a seriesof three time periods and four CO2 concentrations for the 'Fuerte' avocados and twotime periods and two concentrations for the 'Hass' avocados. Results weredisappointing, as the fruit treated with CO2 were not able to retain their quality.For the second experiment, 'Fuerte' and 'Hass' avocados were treated with either CAor I-MCP, or CA and I-MCP in combination. Previous research had identified apositive synergistic effect when CA and I-MCP were combined, due to the fact thatthe treatments act at different points in the ethylene production process.Both the CA and I-MCP treatments, whether alone or in combination, had positiveresults in retaining firmness and extending the shelf life of the fruit. The treatmentswere also able to retain the quality of the 'Fuerte' avocados in terms of internal and,external physiological disorders. 'Hass' avocados, however, are known to be ofexcellent internal quality and none of the treatments had a greater percentage of soundfruit than the fruit which were stored in air. The extended ripening gained bytreatment with I-MCP outweighed any increased loss due to fruit quality and in termsof the ease of application makes it superior to CA storage. However, beforelarge-scale commercial application of I-MCP begins, much still needs to be learnedabout its use on avocados.Relative humidity (RH) control, forms an integral part of the storage of many fruit andvegetables. However, the difficulty in controlling and measuring RH has resulted in itbeing largely ignored. Research has shown that storage of fruit and vegetables at RHlevels close to 95% has been able to restrict ripening and chilling injury developmentby decreasing the water stress on the fresh commodities during storage.During the final experiment, 'Fuerte' and 'Hass' avocados were placed at thecommercial storage temperature and a chilling temperature. At each temperature, thefruit were either stored under a high or a low RH. Results were inconclusive, as thehigher RH showed no signs of restricting chilling injury or any other disorders in thefruit.

[发布机构] Stellenbosch University