Thesis (MSc)--Stellenbosch University, 2002. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53212 |
| Date | 12 1900 |
| Creators | Mare, Leon |
| Contributors | Huysamer, M., Holcroft, D. M., Dodd, M. C., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 240 pages : illustrations |
| Rights | Stellenbosch University |
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