Thesis (MScAgric)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The table grape industry uses rapid cooling and packaging to protect grapes from desiccation
and decay. Numerous packaging methods and combinations are used in the industry with
each having their own advantages and disadvantages.
Inferior postharvest grape quality can usually be ascribed to either deficient or excessive
moisture in the carton. Berry split, decay and S02 damage are all disorders that are either
caused or aggravated by wet berries in conjunction with elevated temperature. On the other
hand, grapes that are exposed to desiccating conditions will develop brown stems and cause
ineffective control by S02 gas generators. Moisture management is governed by perforated
or non-perforated liners and/or by placing moisture absorbing materials inside the liners. To
find the optimum liner perforation or moisture sheet combination, 'Thompson Seedless' and
'Red Globe' (Vitis vinifera Linnaeus) table grape quality was evaluated in various trials.
The investigation of non-perforated liners compared to liners with different degrees of
perforation concluded the following: Perforated liners benefit grape quality by decreasing
S02 damage and berry split due to less moisture in the carton. These benefits, however, also
lead to loss in quality due to increased stem desiccation and a lower S02 concentration in the
packaging. The lower moisture content in the carton compensates for the lower S02
concentration, creating an environment less favourable for decay development. S02 damage
and berry split decreased with an increase in degree of liner perforation, irrespective of the
cultivars sensitivity to the disorder. Optimum level of perforation depends on the specific
sensitivity of a cultivar to certain quality disorders and the characteristics of the quality
disorders associated with a cultivar. Additionally, packing conditions such as product
temperature and humidity should be considered. The specific costs associated with the
advantages and disadvantages influenced by the degree of liner perforation will be the
deciding factor in liner selection.
The investigation of a clay-containing, moisture absorbing sheet emphasized the benefits and
risks of absorbing large amounts of water within the packaging. Irrespective of using a
perforated or non-perforated liner the influence of the desiccant sheet was evident throughout
the trials. It benefited grape quality by lowering the incidence of berry split and S02 damage. However, decay control was impaired by the desiccant sheet, and stem desiccation was
aggravated.
The comparison of non-perforated liners with liners of various degrees of perforation showed
the benefit of faster cooling rates of perforated liners. The various perforated liners showed
little variation in airflow and cooling times.
Morphological studies of various cultivars could not ascribe differences in stem condition to
anatomical dissimilarities between various cultivars. It was found that 'Red Globe' had a
much larger berry volume to stem weight ratio contributing to a high rate of water loss and
stem dehydration. Stem visibility is high in 'Red Globe' due to the straggly, loose nature of
the bunches. This heightens the perception of dry, brown stems and overemphasizes the
actual severity of the disorder. / AFRIKAANSE OPSOMMING: Die tafeldruifbedryf gebruik versnelde verkoeling en verpakking om druiwe te beskerm teen
uitdroging en bederf. Verskeie verpakkingsmetodes word gebruik in die industrie waarvan
elkeen sy eie voor- en nadele het.
Ondergeskikte na-oes kwaliteit kan gewoonlik toegeskryf word aan óf te min óf te veel vog
in die karton. Korrelbars, S02 skade en bederf is almal kwaliteitsdefekte wat óf veroorsaak
word, óf vererger word deur nat korrels, saam met 'n verhoging in temperatuur. In
teenstelling hiermee sal druiwe wat blootgestel word aan droë toestande, bruin stingels
ontwikkel en S02 beheer salook ondoeltreffend wees. Vog in verpakking word beheer deur
geperforeerde of nie-geperforeerde binnesakke en/of deur vogabsorberende materiaal binne
die binnesak te plaas. Om die optimum binnesak perforasie of vogabsorberende vel
kombinasie te vind is 'Thompson Seedless' en 'Red Globe' (Vitis vinifera Linnaeus)
tafeldruif kwaliteit ge-evalueer in verskeie proewe.
Die bestudering van nie-geperforeerde binnesakke teenoor binnesakke met verskillende grade
van perforasies het die volgende resultate gelewer: Geperforeerde binnesakke bevoordeel
druif kwaliteit deur die vermindering van S02 skade en korrelbars weens minder vog in die
karton. Hierdie voordele sal egter lei tot verlies in kwaliteit weens die vinniger uitdroging
van stingels en die verlaging van S02 konsentrasie in die verpakking. Die laer vog inhoud in
die karton vergoed vir die vermindering van S02 konsentrasie, omdat minder gunstige
toestande vir die ontwikkeling van bederf geskep word. S02 skade en korrelbars het
verminder met 'n vermeerdering van perforasies, ongeag die kultivar se sensitiwiteit vir die
defekte. Optimum vlakke van perforasie is afhanklik van die spesifieke sensititiwiteit van 'n
kultivar tot sekere kwaliteitsdefekte, en eienskappe van die kwaliteitsdefekte wat geassosieer
word met die kultivar. Boonop moet verpakkingsomstandighede soos produktemperatuur en
humiditeit ook in gedagte gehou word. Die spesifieke koste verbonde aan die voor- en nadele
wat beïnvloed word deur die graad van perforasie sal die bepalende faktor wees wanneer 'n
binnesak gekies word.
Die bestudering van 'n klei-bevattende, vogabsorberende vel het bewys dat dit voordele en
risiko's inhou om groot hoeveelhede vog te absorbeer. Ongeag die gebruik van 'n geperforeerde of nie-geperforeerde binnesak, was die invloed van die desikkante vel duidelik
in al die proewe. Dit was voordelig vir druif kwaliteit deurdat dit korrelbars en S02 skade
verminder het. Bederfbeheer is egter verswak deur die desikkante vel, en stingel uitdroging
IS vererger.
Die vergelyking van nie-geperforeerde binnesakke met verskillende grade van geperforeerde
binnesakke het die voordeel bewys van vinniger verkoelinstempo's van die geperforeerde
binnesak. Verskille in die graad van perforasie het 'n klein invloed gehad op die lugvloei en
verkoelingstempo 's.
Bestudering van verskeie kultivars kon geen morfologiese verskille uitwys wat variasie in
stingelkwaliteit tussen kultivars kan verklaar nie. Dit is bevind dat 'Red Globe' 'n baie groter
korrelvolume tot stingelgewig verhouding het. Stingels is meer sigbaar by 'Red Globe'
weens die yl, los aard van die trosse. Dit verhoog die persepsie van droë, bruin stingels en dit
oorbeklemtoon die voorkoms van die defek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53404 |
| Date | 12 1900 |
| Creators | Du Plessis, S. F. (Stephanus Francois) |
| Contributors | Huysamer, M., Jacobs, G., 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 | English |
| Type | Thesis |
| Format | x, 172 p. : ill. |
| Rights | Stellenbosch University |
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