Evaluation of temperature variances found with integral reefer containers during shipment of Japanese plums (Prunus salicina Lindl.) at dual and single temperature

Kapp, Anine A. C. (Stellenbosch : Stellenbosch University, 2008-03)

Thesis (MScAgric)--Stellenbosch University, 2008.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/21447
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