Thesis (MScAgric)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Stone fruit is susceptible to chilling injury and intermittent warming has been shown to
alleviate chilling injury during cold storage. A dual temperature storage regime was
developed in South Africa for plums based on the principles of intermittent warming. The
regime consists of an initial period at -0.5°C, a variable duration warming period at 7.5°C,
followed by -0.5°C. Refrigerated integral containers were designed to maintain product
temperature and not to reduce product temperature, per se. Considering that dual
temperature shipment requires significant refrigeration and effective distribution of cool air to
remove sensible- and respiratory heat, the capacity of integral containers to ship plums
successfully at dual temperature is questioned.
The objectives of this study were, firstly, to analyse pulp temperature data and possibly
identify different temperature zones within containers shipping plums at dual temperature.
Secondly, to understand the underlying processes differentiating the temperature zones and
thirdly, to determine the effect of container performance on fruit quality.
Three processes were identified as important characteristics of pulp temperature data sets
recorded during dual temperature shipping, namely cooling down, heating up and over
heating in the container. The order of importance differed according to the cultivar shipped
and the container’s performance. Three temperature zones were identified in dual
temperature containers, where the average pulp temperature, time to heat up and time to
cool down for each temperature zone increased along the length, across the width from the
left to the right and up the container system. The variable temperature conditions were
possibly due to a variation in delivery air temperature, poor airflow and the effect of increased
respiration and, therefore, production of vital heat by the fruit. The cooling down process was
identified as the most important process discriminating the temperature zones.
With the exception of ‘Fortune’, variable temperature conditions found within integral
containers shipping plums at dual temperature had a significant influence on the fruit
firmness post-shipment, where deterioration levels increased from the front to the door end
of the container due to an increase in pulp temperature. However, it was also shown that fruit
firmness prior to shipment could have a determining effect on differences found. It could not be proven that variable temperature conditions resulted in significantly higher levels of
internal defects within the integral container.
Temperature zones could not be identified within refrigerated integral containers shipping
plums at single temperature, suggesting that the containers are able to maintain the
temperature well throughout the container area.
A constant 2°C storage temperature could possibly replace the commercial dual temperature
regime in the case of ‘Pioneer’ plums due to improved fruit firmness, similar colour
development to the control and less sensible heat produced in the container resulting in a
more stable container environment. However, unacceptably high levels of shrivel and internal
browning were found. / AFRIKAANSE OPSOMMING: Steenvrugte is vatbaar vir koueskade en dit is bewys dat periodieke verwarming gedurende
koelopberging koueskade kan verlig. Die dubbeltemperatuur opbergingsregime is in Suid-
Afrika ontwikkel vir pruime en is gebaseer op die beginsels van periodieke verwarming. Die
regime bestaan uit ‘n inisiële periode by -0.5°C, ‘n variërende periode by 7.5°C, gevolg deur
-0.5°C. Verkoelde integrale houers is ontwerp om produktemperature te handhaaf en nie
soseer om produktemperatuur te verlaag nie. Die kapasiteit van integrale houers om pruime
suksesvol teen dubbeltemperatuur te verskeep word dus bevraagteken, in ag geneem dat
dubbeltemperatuurverskeping betekenisvolle verkoeling en effektiewe verspreiding van koue
lug vereis om die waarneembare- en respiratoriese hitte te verwyder.
Die doelwitte van die studie was eerstens om die pulptemperatuurdata te analiseer en
moontlik verskillende temperatuursones binne houers wat pruime teen dubbeltemperatuur
verskeep te identifiseer. Tweedens, om die onderliggende prosesse wat die
temperatuursones van mekaar onderskei te verstaan, en derdens om die effek van die houer
se werkverrigting op vrugkwaliteit te bepaal.
Drie prosesse is geïdentifiseer as belangrike eienskappe van pulptemperatuur datastelle
aangeteken gedurende dubbeltemperatuurverskeping, naamlik afkoeling, opwarming en
oorverhitting wat binne die houer plaasvind. Die volgorde van belangrikheid het gevarieer
afhangende van die kultivar verskeep en die houer se werkverrigting. Drie temperatuursones
is geïdentifiseer binne integrale houers wat pruime teen dubbeltemperatuur verskeep, waar
die gemiddelde pulptemperatuur, die opwarmingstyd en die afkoelingstyd vir elke
temperatuursone in die lengte, oor die wydte van links na regs en van onder na bo in die
houersisteem toegeneem het. Die variërende temperatuur toestande kan moontlik toegeskryf
word aan ‘n variasie in leweringstemperatuur, swak lugvloei en die effek van toenemende
respirasie, en dus die produksie van hitte vrygestel deur die vrugte. Die afkoelingsproses is
geïdentifiseer as die belangrikste proses wat die temperatuursones van mekaar onderskei.
Behalwe in die geval van ‘Fortune, het variërende temperatuurtoestande in integrale houers
wat pruime teen dubbeltemperatuur verskeep ‘n betekenisvolle invloed op die vrugfermheid
na verskeping gehad, waar vrugveroudering toegeneem het van voor in die houer na die
deur van die houer as gevolg van ‘n toename in pulptemperatuur. Daar is egter bewys dat die vrugfermheid voor verskeping ook ‘n bepalende effek kon hê op die fermheidsverskille.
Dit kon nie bewys word dat die variërende temperatuurtoestande betekenisvol hoër vlakke
van interne defekte binne die integrale houer veroorsaak het nie.
Temperatuursones kon nie geïdentifiseer word binne verkoelde integrale houers wat pruime
teen enkeltemperatuur verskeep het nie, wat dus impliseer dat die houers daartoe instaat is
om temperatuur goed te onderhou binne die houer.
‘n Konstante 2°C opbergingstemperatuur kan moontlik die kommersiële
dubbeltemperatuurregime vervang in die geval van ‘Pioneer’ pruime as gevolg van
verbeterde vrugfermheid, soortgelyke kleurontwikkeling as die dubbeltemperatuurregime en
minder hitte geproduseer binne die houer deur die pruime, wat ‘n meer stabiele
houeromgewing veroorsaak. Onaanvaarbare hoë vlakke van verrimpeling en interne
verbruining is egter gevind.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21447 |
| Date | 03 1900 |
| Creators | Kapp, Anine A. C. |
| Contributors | Huysamer, M., Jacobs, G., Theron, K. I., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | x, 161 leaves : ill. |
| Rights | Stellenbosch University |
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