Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Inadequate cooling of produce after it has been packed into ventilated packaging can result in
inconsistent fruit quality. Misalignment of ventilation holes during stacking as well as the use of
internal packaging, such as trays, polyliner bags and thrift bags reduces airflow distribution through
the packaging. Consequently, the complex needs of maintaining the cold chain of perishable
produce and the considerable variations in packaging designs have made it challenging to find an
optimal ventilated package and stacking arrangement. The aims of this study were, therefore, to
assess the status of ventilated packaging in the South African pome fruit industry, and to
characterize the effects of package design and multi-scale packaging components on the resistance
to airflow and cooling performance of apples under forced-air cooling conditions.
A survey of the pome fruit industry identified over twenty packaging designs which were
grouped into eleven unique designs and further categorised into either ‘display’ or ‘telescopic’
designs. Although South African fruit industry standards recommend ventilation areas of at least
5%, the ventilation areas of package designs identified from the survey varied considerably between
<1 and 11%. Furthermore, the study showed that use of stacking renders many of the ventilation
holes ineffective, due to blockages from adjacent cartons.
The contribution of each component of the multi-scale packages used for handling apples was
determined by analysis of pressure drop during forced-air cooling. The results showed when
utilising a combination of cartons, fruit trays and plastic liner bags, the total pressure drop
contribution of the cartons (8%) and fruit trays (3%) was minimal, while the use of plastic liner
bags contributed 89%. However, in a carton and thrift bag packaging combination, the thrift bags
contributed 66% to the pressure drop while the carton contributed 34%.
The cooling results indicated a negative correlation between the total stack ventilation area and
the cooling heterogeneity. In addition, the airflow velocity was correlated positively with fruit
cooling rate and negatively with total moisture loss. Fruit packed inside polyliner bags had cooling
rates four times slower than fruit on trays and three times slower in thrift bags. The use of liner bags
blocked the ventilation holes, thereby reducing the airflow velocity. As a result of the longer
cooling times in the polyliner bags, fruit remained at higher temperatures for longer periods,
resulting in up to three times more moisture loss during forced-air cooling. In addition, a
temperature gradient formed due to a progressive increase in air temperature through the stack,
thereby resulting in a similar gradient of moisture loss. This research showed that airflow velocity and distribution were the most important factors
contributing to the effectiveness of fruit cooling in multi-scale packaging. From a cold chain
perspective, future packaging designs should therefore focus on optimising ventilation
characteristics and alignment during stacking to ensure adequate airflow. Given the contribution of
internal packaging to high resistance to airflow, such packaging components should be used with
caution and only when necessary to meet physiological and market requirements. / AFRIKAANSE OPSOMMING: Onvoldoende verkoeling van vars produkte nadat hulle verpak is kan lei tot wisselende
vruggehalte. Wanbelyning van ventilasiegate tydens stapeling sowel as die gebruik van interne
verpakking soos rakkies (eng. “trays”), poli-etileensakke en drasakkies (eng. “thrift bag”) verminder
die lugverspreiding deur die verpakking. Komplekse behoeftes om bederfbare produkte in die koue
ketting te behou en die aansienlike verskille in verpakkingsontwerpe het dit 'n uitdaging gemaak om
'n optimale geventileerde verpakking en stapelskikking of -rangskikking te vind. Die doelwitte van
hierdie studie was dus om die status van geventileerde verpakking in die Suid-Afrikaanse
kernvrugbedryf te asseseer, en die gevolge van die verpakkingsontwerp en multi-skaal
verpakkingskomponente op die weerstand teen lugvloei en verkoeling van appels onder geforseerde
lugverkoeling te bepaal.
‘n Opname van die kernvrugbedryf het meer as twintig verpakkingsontwerpe geïdentifiseer, wat
in elf unieke ontwerpe gegroepeer is en verder getipeer word in ‘vertoon’ en ‘teleskopiese’
kartonontwerpe. Alhoewel die Suid-Afrikaanse vrugindustrie-standaarde ventilasie areas van ten
minste 5% aanbeveel, het die ventilasie areas van die verpakkingsontwerpe geïdentifiseer uit die
opname aansienlik gewissel tussen <1 en 11%. Verder het die studie getoon dat gebruik van
stapeling baie van die ventilasiegate ondoeltreffend laat weens blokkasies veroorsaak deur
aangrensende kartonne.
Die bydrae van elke komponent van die multi-skaal verpakkingskombinasies gebruik vir die
hantering van appels was bepaal deur analise van die afname in lugdruk tydens geforseerde
lugverkoelingskondisies. Die resultate het getoon dat wanneer ‘n kombinasie van kartonne, polietileensakke
en vrugte plus rakkies gebruik word, die bydrae van die kartonne (8%) en vrugte plus
rakkies (3%) tot die totale afname in lugdruk minimaal was, terwyl die gebruik van polietileensakke
‘n 89% bydrae gemaak het. In ‘n karton en drasakkie kombinasie het die drasakkies
66% bygedra tot die afname in lugdruk, terwyl die karton 34% bygedra het.
Die verkoelingsresultate het 'n negatiewe korrelasie getoon tussen die totale stapelventilasie-area
en die verkoelingsheterogeniteit. Daarbenewens was die lugvloeisnelheid positief gekorreleer met
vrugverkoelingstempo en negatief gekorreleer met totale vogverlies. Die verkoelingstydperk van
vrugte in die poli-etileensakke was vier keer langer as die rakkie met vrugte kombinasie en drie
keer langer in die drasakkies. Die poli-etileensakke het die ventilasiegate versper en dus die
lugvloeisnelheid verlaag. Weens die langer verkoelingstye in die poli-etileensakke was vrugte veel langer aan hoër temperature blootgestel, wat uiteindelik gelei het tot drie keer meer massaverlies
gedurende geforseerde lugverkoeling. Daarby het ‘n temperatuurgradiënt gevorm as gevolg van ‘n
progressiewe verhoging in lugtemperatuur deur die stapel wat gelei het tot ‘n gelykstaande gradiënt
van vogverlies.
Hierdie navorsing het getoon dat die lugvloeisnelheid en -verspreiding die belangrikste faktore
was wat die doeltreffendheid van vrugverkoeling in multi-skaal verpakking geaffekteer het. Uit 'n
koelketting perspektief moet die toekomstige verpakkingsontwerpe dus fokus op die optimalisering
van ventilasie eienskappe en belyning (eng. “alignment”) tydens stapeling om voldoende lugvloei te
verseker. Gegewe die bydrae van die interne verpakking tot hoë weerstand teen lugvloei, moet sulke
verpakkingskomponente met omsigtigheid gebruik word en slegs wanneer dit nodig is om aan
markvereistes te voldoen.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85685 |
| Date | 12 1900 |
| Creators | Berry, Tarl Michael |
| Contributors | Opara, U. L., Delele, M. A., Meyer, C., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Format | ix, 132 p. : ill. |
| Rights | Stellenbosch University |
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