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Cooling and shipping studies on table grapes (Vitis vinifera L.)Ngcobo, Mduduzi E. K. 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Fruit quality is the most important factor that determines prices for the fruit in the
international markets. Although different consumers perceive quality differently there are
quality variables that are always associated with poor quality by all consumers. In table
grapes (Vitis vinifera L.) these variables may include overall appearance, stem condition,
SO2 damage, decay, berry browning and shatter. The presence of these quality defects
negatively affects prices and most often results in quality claims.
Cooling is the most widely used method to reduce the postharvest loss of fruit quality. In
South Africa, most deciduous fruits including table grapes are forced air cooled to a
statutory pulp temperature of –0.5°C prior to shipping in an effort to preserve quality,
thus ensuring good market prices for the fruits. Despite these efforts, there are still quality
claims from the markets and this reduces the returns to the growers.
The objectives of this research were to: (i) see if cooling time can be reduced by cooling
to higher pulp temperatures of 1.5°C and 3°C without causing quality losses, thus
improving the throughput of the cold rooms; (ii) see if the problem of berry browning can
be alleviated by cooling grapes to higher pulp temperature, and (iii) see whether pallet
positioning in the cooling tunnels and reefer container affect quality.
The trends showed better quality when ‘Victoria’ and ‘Regal Seedless’ were forced air
cooled (FAC) to pulp temperatures of 1.5 °C and 3 °C as opposed to –0.5 °C. There were
no economic losses associated with pre-cooling grapes to pulp temperatures of 1.5 °C and
3 °C. There were no significant differences in berry browning related to pre-cooling
treatments. However, cooling time was reduced significantly. In most of the cooling
tunnels and reefer containers used in this trial, grape quality results showed no significant
differences between the positions in the stack and in reefer containers. However, in cases
where there were significant differences, the middle and the rear positions showed better
grape quality in terms of stem condition (dry and brown stems) than the front position
(near fan) in both the pre-cooling stack and reefer containers. The trends showed that the front is cooler than the back of the pre-cooling stack. The pulp
temperature differences between the front and rear positions in the reefer container were
as high as 1.23 °C. The trends also showed that the bottom layers of the pallets were
cooler than the top layers in the reefer container.
FAC to 3°C resulted in a constant reduction in percentage electrolyte leakage after 4
weeks of storage at –0.5°C, while FAC to 1.5°C, -0.5°C and static room cooling (control)
in some cases showed an initially low electrolyte leakage followed by an increase in
leakage after 4 weeks of storage.
FAC grapes to higher pulp temperatures of 3°C and 1.5°C could reduce the cooling time,
thereby improving the throughput of cold rooms. There was no clear evidence to suggest
that browning was due to pre-cooling practices. Both preharvest and postharvest
conditions need to be further investigated to better understand the problems of browning
in white table grapes. / AFRIKAANSE OPSOMMING: Vrugkwaliteit is ʼn kritiese faktor in die bepaling van pryse op die internasionale markte.
Alhoewel daar variasie voorkom tussen verbruikers in wat vrugkwaliteit is, bly sekere
aspekte altyd onveranderd. Ononderhandelbare kwaliteit aspekte in tafeldruiwe (Vitis
vinifera L.) sluit die algemene voorkoms, toestand van die trosstingels, SO2 skade,
bederf, korrel verbruining en los-korrels in. Indien enige van die kwaliteit-defekte
voorkom het dit ʼn negatiewe impak op die prys en lei gewoonlik tot gehalte eise.
Verkoeling word algemeen gebruik om die verlies van na-oes kwaliteit te verminder. Die
meeste sagtevrugte geproduseer in Suid Afrika (insluitend tafeldruiwe) ondergaan
geforseerde verkoeling tot ʼn statutêre pulptemperatuur van -0.5°C, voor verskeping.
Ondanks hierdie maatreëls om hoë pryse te verseker, is daar steeds kwaliteiteise in die
mark wat lei tot ‘n laer inkomste vir produsente.
Die navorsing het dus ten doel gehad om : (i) te bepaal of die tyd van verkoeling
verminder kan word, indien na hoër pulptemperature van 1.5°C en 3°C verkoel kan word,
sonder ‘n verlies in kwaliteit en sodoende die deurvloeitempo van die koelkamers
verhoog; (ii) om te bepaal of die voorkoms van korrelverbruining verlaag kan word
indien tot hoër pulp-temperature verkoel word, en (iii) laastens om te bepaal of posisie
van die palet in die verkoelingstonnel en verskepingshouer ʼn invloed het op
vrugkwaliteit.
Tendense toon dat ‘Victoria’ en ‘Regal Seedless’ kwaliteit beter was indien verkoel tot
pulptemperature van 1.5°C en 3°C in vergelyking met -0.5°C. Daar was geen
ekonomiese verliese waargeneem indien die hoër verkoelingstemperature gebruik is nie.
Alhoewel daar geen betekenisvolle verskille in korrelverbruining voorgekom het tussen
temperatuur behandelings nie is die verkoelingsperiode verkort. In die meeste van die
verskepingshouers, asook in posisies tydens geforseerde verkoeling is daar geen
betekenisvolle verskille waargeneem nie. In die gevalle waar daar egter wel betekenisvolle verskille voorgekom het, het die middel en agter posisies beter
vrugkwaliteit gehad as die voorste posisie tydens verkoeling asook houerverskeping.
Die palette aan die voorkant (naby die waaier) het as ʼn algemene tendens laer
temperature as in die agterkant van die verkoelingstonnel. Verskille in pulptemperature
tussen palette in die voor en agterkant van verskepingshouers was so hoog as 1.23°C. Die
temperatuurdata het uitgewys dat die onderste laag kartonne neig om by ‘n laer
temperatuur te wees as die boonste lae kartonne tydens houerverskeping.
Geforseerde verkoeling teen 3°C het gelei tot ‘n afname in persentasie elektrolietlekkasie
na 4 weke van verkoeling teen -0.5°C. Terselfdertyd het geforseerde verkoeling tot 1.5°C
en -0.5°C asook statiese verkoeling (kontrole) in sekere gevalle gelei tot ‘n laer
aanvanklike uitlek van elektrolietlekkasie, gevolg deur ʼn verhoging na 4 weke opberging.
Geforseerde verkoeling van tafeldruiwe tot pulptemperature van 1.5°C en 3°C verkort die
verkoelingstyd en verhoog dus die deurvloeitempo in die verkoelingskamers. Daar was
gedurende die studie geen duidelike bewyse gevind dat korrelverbruining voorkom as
gevolg van verkoelingspraktyke nie. Beide voor en na-oes praktyke sal verder ondersoek
moet word om die invloed daarvan te bepaal op die verbruining van wit tafeldruiwe.
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Effects of packaging and postharvest cooling on quality of table grapes (Vitis vinifera L.)Du Plessis, S. F. (Stephanus Francois) 12 1900 (has links)
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.
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