Various storage techniques of plums and avocados

Mare, Leon (2002-12)

Thesis (MSc)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: Historically the storage of South African plum fruit involved cold storage at single low temperatures (-O.5°C). The ever present problem of internal breakdown, however, led to the development of the dual temperature storage regime (a type of intermittent warming) which was found to restrict the level of internal breakdown. However, this temperature regime led to the development of or unmasking of gel breakdown (GB). During season one it was proposed that 'Songold' and 'Angeleno' plums could be stored at a single high temperature (7.5°C) during the shipping period (18 days) in combination with controlled atmospheres (CA). This was compared to the commercially used dual temperature regime (10 days at -O.5°C and eight days at 7.5°C). During season two the temperature regimes were adjusted to mirror the storage of the fruit from the date of harvest until the fruit is purchased. During the shipping period the dual temperature regime and the single high temperature regime were still compared. It was hypothesised that the fruit could be stored at the higher temperature in combination with CA during shipping, and this would allow the ripening 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 with CA had a positive influence on delaying the ripening of the fruit. Most noticeable was the delay of fruit softening and the restriction of colour and GB development of the 'Songold' plums. Most importantly, these results were achieved without the fruit being exposed to the low, injurious temperatures associated with the dual temperature regime. It was, however, concluded that due to the suppressed climacteric trait of these plums more benefit could be gained from the higher temperature storage in combination 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 has risen to about 95% of the exported fruit. CA storage of avocados has shown positive results in retaining fruit firmness, restricting disorder development and extending the shelf life. Recently, research with l-methylcyclopropene (l-MCP) storage of avocados has been found to be as successful as CA storage and there is a belief that it will be the answer to storage for the avocado industry once registered for commercial use. During the first experiment, 'Fuerte' and 'Hass' avocados were treated with CO2 shocks (C02 levels which greatly exceed the initial intercellular concentrations of CO2 are known as CO2 shock treatments). These shock treatments were done over a series of three time periods and four CO2 concentrations for the 'Fuerte' avocados and two time periods and two concentrations for the 'Hass' avocados. Results were disappointing, 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 CA or I-MCP, or CA and I-MCP in combination. Previous research had identified a positive synergistic effect when CA and I-MCP were combined, due to the fact that the treatments act at different points in the ethylene production process. Both the CA and I-MCP treatments, whether alone or in combination, had positive results in retaining firmness and extending the shelf life of the fruit. The treatments were 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 of excellent internal quality and none of the treatments had a greater percentage of sound fruit than the fruit which were stored in air. The extended ripening gained by treatment with I-MCP outweighed any increased loss due to fruit quality and in terms of the ease of application makes it superior to CA storage. However, before large-scale commercial application of I-MCP begins, much still needs to be learned about its use on avocados. Relative humidity (RH) control, forms an integral part of the storage of many fruit and vegetables. However, the difficulty in controlling and measuring RH has resulted in it being largely ignored. Research has shown that storage of fruit and vegetables at RH levels close to 95% has been able to restrict ripening and chilling injury development by decreasing the water stress on the fresh commodities during storage. During the final experiment, 'Fuerte' and 'Hass' avocados were placed at the commercial storage temperature and a chilling temperature. At each temperature, the fruit were either stored under a high or a low RH. Results were inconclusive, as the higher RH showed no signs of restricting chilling injury or any other disorders in the fruit.

AFRIKAANSE OPSOMMING: In die verlede is pruime in Suid Afrika opgeberg volgens 'n enkeltemperatuur-regime (-0.5°C). Interne verval (IV) van die pruime was 'n probleem en het gelei tot die ontwikkeling van die dubbeltemperatuur-opberging regime wat IV verhoed het. Dit het egter gelei tot die ontwikkeling of ontmaskering vanjelverval (IV). Vir seisoen een is voorgestel dat die opberging van 'Songold' en 'Angeleno' pruime gedurende die verskepingstyd (18 dae), teen 'n hoë enkeltemperatuur van 7.5°C gekombineerd met beheerde atmosfeer (BA) geskied. Dit is vergelyk met die kommersiële dubbeltemperatuur-opberging regime (10 dae by -0.5°C en agt dae by 7.5°C). Vir seisoen twee is die temperatuur regime aangepas om die opberging van die vrug vanaf die oesdatum totdat dit deur die verbruiker gekoop word, na te boots. Tydens die verskepingstyd is die dubbeltemperatuur-opberging regime steeds vergelyk met die enkeltemperatuur opberging. Die gestelde hipotese is dat die vrugte gedurende verskeping by hoë enkeltemperatuur gekombineerd met BA opgeberg kon word. Sodoende word rypwording vertraag en die kwaliteit van die vrug behou sonder dat die vrugte blootgestel word aan temperature wat koueskade sal veroorsaak. By beide kultivars het 'n hoë enkeltemperatuur, gekombineer met BA opberging, die rypwording van die vrugte vertraag. Mees opmerklik was die vertraging van die sagwording van altwee kultivars asook die vertraging van kleur ontwikkeling en JV van die 'Songold' pruime. Wat van belang is, is dat die resultate bereik is sonder dat die vrugte blootgestel was aan die lae temperature wat koueskade veroorsaak. Die onderdrukte klimakterium wat met 'Songold' en 'Angeleno' pruime verkry is toon dat pruim kultivars met sterker rypwordingspatrone meer sal baat deur opberging by hoë temperature saam met BA. In teenstelling met die pruim bedryf, word omtrent 95% van die avokado vrugte wat deur Suid Afrika uitgevoer word onder BA verskeep. BA opberging toon vir baie jare al dat dit 'n positiewe invloed op die vertraging van sagwording, die behoud van gehalte en die verlenging van die raklewe van avokados het. Onlangse navorsing het aangetoon dat I-metielsiklopropeen (I-MCP) 'n produk is wat BA opberging se plek kan inneem. Daar word geglo dit is die antwoord vir avokado opberging in Suid Afrika. Vir die eerste eksperiment het 'Fuerte' en 'Hass' avokados 'n CO2 skok behandeling ontvang (C02 vlakke wat die interne sellulêre konsentrasie van C02 oorskrei). Die skok behandelings was oor drie tydperke en vier konsentrasie vlakke gedoen vir die 'Fuerte' avokados en oor twee tydperke en twee konsentrasies vir die 'Hass' avokados. Die resultate was teleurstellend omdat die vrugte wat met die C02 behandel is nie hul gehalte kon behou nie. Gedurende die tweede eksperiment, was 'Fuerte' en 'Hass' avokados met BA of I-MCP, alleen of in kombinasie behandel. Navorsing het bewys dat daar 'n dubbelle effek is as BA en I-MCP saam gebruik word, omdat hulle etileen produksie deur verskillende maniere beheer word. Beide die BA en I-MCP behandelings, alleen of in kombinasie, het 'n positiewe effek uitgeoefen op die vrug deurdat dit fermheid behou en die raklewe verleng het. Die behandelinge het ook die kwaliteit van die 'Fuerte' avokados behou. 'Hass' is 'n avokado wat alreeds 'n baie goeie interne kwaliteit het. Vir dié rede het die vrugte wat net in lug opgeberg was die beste interne kwaliteit gehad. Maar die verlengde raklewe agv. die I-MCP behandeling is van groter belang as die kwaliteit wat verloor is. Dit, saam met die feit dat die toepassing van I-MCP behandeling baie makliker is as BA, maak dit die beter opsie. Voordat I-MCP kommersiël geregistreer is moet daar egter nog baie geleer word oor die produk sodat dit so effektief as moontlik gebruik kan word vir die opberging van avokados. Die beheer van relatiewe humiditeit (RH) word beskou as 'n groot veranderlike in die opberging van vrugte en groente. RH word egter meestal geïgnoreer in opberging omdat die beheer en meet daarvan moeilik is. Navorsing het al getoon dat indien die RH vlakke, gedurende opberging, nabyaan 95% gehou word, kan koueskade verlaag word deur die water dampdruk tekorte op die vars produkte te verlaag. Vir die finale eksperiment was 'Fuerte' en 'Hass' avokados opgeberg teen die kommersiële temperatuur sowel as 'n laer temperatuur. By beide temperature was die RH gewysig om laag of hoog te wees. Resultate was egter teleurstellend omdat die hoër RH nie koue skade of ander fisiologiese skade vertraag het nie.

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