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.

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.