Thesis (MScAgric) -- University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Postharvest berry split and abscission are prevailing physiological disorders that negatively impact on the quality of table grapes exported from South Africa. Inferior grape quality due to these disorders results in a considerable decline in consumer confidence in the branded product, which leads to a drop in demand, and consequently, lower prices. Since information concerning postharvest factors influencing postharvest berry split and abscission is limited, the search for reliable methods to adequately control these problems remains elusive. In an attempt to obtain the required information, the influence of harvest temperature, harvest maturity, perforated liners, field heat removal prior to packing, delay periods before and after packing, storage duration and the elevation of storage temperature on the development of berry split and abscission in 'Thompson Seedless' (Vitis vinifera Linnaeus) table grapes was investigated. Changes in abscission related factors during berry development, and the influence of pre-and postharvest ethylene inhibitors on the development of berry abscission in 'Waltham Cross' table grapes, was also studied. Berry split was aggravated by packing 'Thompson Seedless' grapes at high pulp temperatures of approximately 30°C, especially if the grapes were packed in non-perforated bags. The incidence of berry split could be reduced by between 80 and 90% by packing grapes in perforated instead of non-perforated liners. Perforated bags also reduced levels of S02 damage. However, due to significantly more moisture loss from grapes in perforated bags, compared to non-perforated bags, the risk of higher fruit and stem desiccation and softer berries existed. Optimum size and density of perforations needs to be determined to reduce berry split without excessive loss of moisture from the grapes, and S02gas from the air space surrounding the product. The influence of harvest temperature and liner type on berry abscission was not conclusive. Advanced maturity increased grape resistance to berry split. However, grapes harvested too mature were prone to stem desiccation and the development of Botrytis decay. The occurrence of berry abscission also appeared to increase with advanced harvest maturity. Consequently, to ensure optimal post-storage quality, 'Thompson Seedless' grapes should be harvested as soon as horticultural maturity has been reached, which appears to be at approximately 18°Brix. Field heat removal for 1.5 hours at 19°C prior to packing had no beneficial or adverse effect on berry split and abscission. Delay periods prior to packing aggravated berry abscission, but did not influence berry split significantly. Grapes delayed for 12 hours showed a significant increase in berry abscission and Botrytis decay, compared to grapes delayed for only 3 or 8 hours. Considering that the absence of fungal decay is the most important quality prerequisite in table grapes, it is of vital importance to pack grapes with as short a delay period as possible. Grapes packed in non-perforated liners and delayed for different durations after packing, before the onset of forced-air cooling (FAC), showed significant differences regarding the incidence of berry split. Grapes delayed for 18 hours had significantly higher levels of berry split directly after the delay period, compared to grapes delayed for 6 or 12 hours. No significant difference in berry abscission occurred between grapes delayed for different periods. To minimise the amount of berry split, FAC should be applied as rapidly as possible after the packing of grapes in non-perforated liners. Two storage related factors significantly influenced the incidence of berry split in 'Thompson Seedless' grapes during cold storage significantly, viz. the duration of storage at -O.soC,and the increase in temperature after low temperature storage. Berry split increased almost linearly with prolonged storage at -O.soC. An elevation of storage temperature from -O.soC to 10°C any time during the cold storage period, further aggravated the split problem. Consequently, the reduction of berry split in 'Thompson Seedless' table grapes during cold storage requires (a) the shortest possible cold storage period, and (b) good temperature management throughout distribution, from initiation of cooling until the final point of sale. The grape berry abscission potential, as quantitatively indexed by the measurement of the fruit removal force (FRF), showed significant changes during berry development of 'Waltham Cross' table grapes, from 27 to 111 days after full bloom (OAFB). This showed that at certain stages of fruit growth, 'Waltham Cross' grapes are more prone to berry abscission. At 27 OAFB, when the berries had an average diameter of 6.6mm, the grape bunches showed a significantly higher potential for berry abscission, compared to grapes sampled at a later stage. 'Waltham Cross' has inherently straggly bunches with bare shoulders. Therefore, any abscission during berry development will aggravate the problem. Consequently, it is of vital importance that any adverse factors such as moisture stress be avoided, especially during the period when 'Waltham Cross' grapes appear to be very susceptible to berry abscission. Of all parameters measured, moisture loss showed the best correlation with abscission. Grapes harvested with total soluble solids (TSS) of 12.3°Brix, 83 OAFB, had a significantly higher abscission potential than grapes harvested more mature. Therefore, by harvesting 'Waltham Cross' grapes at optimum maturity, at a TSS of approximately 16.4°Brix, berry abscission can be reduced to a great extent. It was evident that at veraison, the metabolism of grape berries changes drastically, and additional to the rapid increase in sugars and the rapid decrease in acidity, a decrease in FRF occurs. Preharvest sprays of ReTain™ (a derivative of aminoethoxyvinylglycine), which inhibits ethylene synthesis, showed no promise as a means to reduce postharvest berry abscission. A postharvest treatment with EthylBloc® (1-methylcyclopropene), which inhibits ethylene action, only reduced berry abscission during one season. / AFRIKAANSE OPSOMMING: Die fisiologiese defekte korrelbars en los korrels wat algemeen voorkom tydens opberging van sekere tafeldruif-kultivars, het 'n negatiewe invloed op tafeldruiwe wat uitgevoer word vanaf Suid-Afrika. Minderwaardige kwaliteit as gevolg van hierdie defekte het 'n aansienlike afname in verbruikers-vertroue tot gevolg wat aanleiding gee tot 'n ooreenkomstige afname in aanvraag en prys van die produk. Inligting rakende na-oes faktore wat die voorkoms van korrelbars en los korrels beïnvloed is beperk, en geen gewaarborgde metode bestaan om hierdie twee defekte volkome te beheer nie. In 'n poging om dié gewenste inligting te bekom, is ondersoek ingestel na die effek van oes-temperatuur, oes-rypheid, geperforeerde sakke, veldhitte verwydering voor verpakking, vertragingsperiodes voor en na verpakking, tydsduur van opberging, en die verhoging van die opbergingstemperatuur, op die voorkoms van korrelbars en los korrels by 'Thompson Seedless' (Vitis vinifera Linnaeus) druiwe. Daar is ook ondersoek ingestel na veranderings in afsnoering verwante faktore tydens korrel-ontwikkeling, en die invloed van vooren na-oes toedienings van etileen inhibeerders op die ontwikkeling van los korrels by 'Waltham Cross'tafeldruiwe. Korrelbars is vererger deur 'Thompson Seedless' met hoë pulptemperature van ongeveer 29.5°C te verpak, veral indien dit in 'n riie-geperforeerde sak verpak is. Die voorkoms van korrelbars kon tussen 80 en 90% verminder word deur 'Thompson Seedless' druiwe in geperforeerde sakke te verpak, in plaas van nie-geperforeerde sakke. Geperforeerde sakke het ook S02 skade op die druiwe verminder. Tog, as gevolg van betekenisvol meer vogverlies vanaf druiwe in geperforeerde sakke as vanaf druiwe in nie-geperforeerde sakke, bestaan die risiko van meer stingel-uitdroging en minder ferm korrels indien druiwe in geperforeerde sakke verpak word. Optimale grootte en digtheid van perforasies moet bepaal word om korrelbars te verminder, maar sonder oormatige vogverlies vanaf die druiwe en oormatige verlies aan S02. Die invloed van oes-temperatuur en sak-tipe op los korrels was nie oortuigend nie. Gevorderde oes-rypheid het die druif se weerstand teen korrelbars verhoog. Daarteenoor was druiwe wat té ryp geoes is, meer gevoelig vir stingel-uitdroging en Botrytis bederf. Dit wilook voorkom of die voorkoms van los korrels toeneem met gevorderde rypheid. Dus, om optimum kwaliteit na opberging te verseker, moet 'Thompson Seedless' geoes word sodra hortologiese rypheid bereik word, wat blyk om by 'n totale opgeloste vaste stof-inhoud (TOVS) van ongeveer 18°Brix te wees. Veldhitte verwydering voor verpakking, vir 1.5 uur by 19°C, het geen effek gehad op die voorkoms van korrelbars en los korrels nie. 'n Vertragingsperiode voor verpakking het die los korrel-probleem vererger, alhoewel dit geen betekenisvolle invloed op die voorkoms van korrelbars gehad het nie. Druiwe wat vir 12 uur voor verpakking vertraag is, het betekenisvol meer los korrels en Botrytis bederf getoon, in vergelyking met druiwe wat slegs 'n vertragingsperiode van 3 of 8 uur ondergaan het. Aangesien die afwesigheid van bederf die belangrikste kwaliteits-vereiste vir tafeldruiwe is, is dit van kardinale belang om druiwe so gou as moontlik na oes te verpak. Druiwe, verpak in nie-geperforeerde sakke, wat vir verskillende periodes vertraag is voor geforseerde-lug verkoeling, het betekenisvolle verskille getoon betreffende die voorkoms van korrelbars. Druiwe vertraag vir 18 ure voor verkoeling, het betekenisvol meer korrelbars getoon, soos gemeet onmiddellik na die vertragingsperiode, in vergelyking met druiwe wat slegs vir 6 of 12 ure vertraag was. Geen betekenisvolle verskille in los korrels het voorgekom tussen druiwe wat verskillende vertragingsperiodes ondergaan het nie. Om korrelbars te verminder, moet geforseerde-lug verkoeling so gou as moontlik na verpakking van druiwe in nie-geperforeerde sakke toegepas word. Twee opbergings-verwante faktore beïnvloed die voorkoms van korrelbars by 'Thompson Seedless' druiwe tydens koelopberging, naamlik die tydsduur van opberging by -O.soC,asook 'n styging in temperatuur vanaf -O.soC tot 1DoC. Korrelbars het feitlik liniêr toegeneem met verlengde opberging by -O.soC. 'n Styging in temperatuur vanaf -O.SoCtot 1DoCop enige tydstip gedurende die koelopbergingsperiode, het korrelbars verder vererger. Dus, om korrelbars by 'Thompson Seedless' tydens opberging tot die minimum te beperk, moet die tydsduur van opberging so kort as moontlik wees, en moet die koue ketting regdeur die distribusie-proses gehandhaaf word, vanaf inisiëring van verkoeling tot en met die uiteindelike verkoop van die produk. Die afsnoerings-potensiaal van druiwe, soos kwantitatief geïndekseer is deur meting van die vrug-verwyderings-vermoë (VVV), het betekenisvol verander gedurende korrel-ontwikkeling van 'Waltham Cross' tafeldruiwe, vanaf 27 tot 111 dae na volblom (DNVB). Dit het getoon dat 'Waltham Cross' druiwe by sekere stadiums van vrug-groei meer gevoelig is vir korrel afsnoering. By 27 DNVB, wanneer die korrels 'n gemiddelde deursnee van 6.6mm gehad het, het die druiwe 'n betekenisvolle hoër potensiaal vir afsnoering getoon, in vergelyking met druiwe wat op 'n latere stadium getoets is. 'Waltham Cross' is inherent geneig tot yl trosse met kaal skouers, gevolglik sal enige afsnoering tydens korrel-ontwikkeling die probleem vererger. Dus is dit van kardinale belang dat enige nadelige faktor, soos byvoorbeeld vogstres, vermy moet word, veral gedurende periodes wanneer dit wil voorkom of 'Waltham Cross' baie vatbaar is vir korrel afsnoering. Van al die parameters wat gemeet is, het vogverlies die beste korrelasie met korrel afsnoering getoon. Druiwe wat 83 DNVB, by 'n TOVS van 12.3°Brix geoes is, het 'n betekenisvol hoër potensiaal vir korrel afsnoering getoon, in vergelyking met druiwe wat ryper geoes is. Dus, deur 'Waltham Cross' druiwe by optimum rypheid te oes, by 'n TOVS van ongeveer 16.4°Brix, kan korrelbars in 'n groot mate verminder word. Tydens verelson, wanneer die metabolisme van die druiwe drasties verander, was daar gepaardgaande met die drastiese toename in TOVS en die drastiese afname in totale titreerbare sure (TSS), ook 'n afname in Voor-oes bespuitings met ReTain™, wat etileen sintese inhibeer, het geen potensiaal getoon om los korrels by 'Waltham Cross' te verminder nie. 'n Na-oes behandeling met EthyIBloc®, wat etileen werking inhibeer, het slegs korrel afsnoering in een van die seisoene effens verminder.

Thesis (MScAgric)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Red colour development on bi-coloured apples and pears ensures better prices for producers. The use of postharvest irradiation to improve colour has been successful on apples, and the objectives of this thesis were to optimise conditions during irradiation for apples and to evaluate the effects of irradiation on pears. 'Cripp's Pink' apples responded to postharvest irradiation with high-pressure sodium (HPS) lights by developing a red blush, whereas the response to irradiation with UV 8 plus incandescent lights was less effective. '8raeburn' apples held at -0.5°C for 4 or 8 weeks prior to irradiation showed a decrease in hue angle and an increase in anthocyanin concentration after 72 hours of irradiation with HPS lamps. In 'Forelle' pears treated in the same way, neither colour development nor anthocyanin synthesis was affected by irradiation. '8raeburn' and 'Cripp's Pink' apples picked weekly for 5 weeks until the optimum harvest date were irradiated with HPS lights. A significant increase in fruit colour was only measured in mature fruit of both cultivars. 'Cripp's Pink' apples were harvested from two production areas with different microclimates, namely, Ceres and Grabouw, and stored for 0, 2 or 5 days at -0.5 °C before irradiation for 120 hours at either 6°C or 20°C. Fruit from Ceres that were irradiated immediately after harvest developed better colour at 6 °C than at 20°C. The differences between fruit irradiated at the two temperatures were no longer significant after 5 days of cold storage prior to irradiation. Fruit from Grabouw consistently developed better colour when irradiated at 6°C than at 20°C. Colour development slightly after 5 days of cold storage prior to irradiation. In another experiment, fruit from both areas were stored at -0.5°C for 20 days before irradiation at either 6°C or 6/20°C. The fluctuating temperature regime resulted in decreases in hue angle of 70° and 65° for the fruit from Grabouw and Ceres, respectively. The decreases were smaller (±200) when fruit were irradiated at 6°C. The hue angle value of well-coloured 'Cripp's Pink' apples held at 3rC under HPS lights for 144 hours increased from 29.3° to 48.3°, and anthocyanin concentration decreased from 739.9 IJg·g·1to 283.6 IJg·g·1. Control fruit held at the same temperature in the dark did not show any change in hue angle value or anthocyanin concentration. 'Bon Rouge' and 'Red d' Anjou', two full red pear cultivars, irradiated with HPS lights for 72 hours, showed no significant changes in hue angle. 'Forelle' pears, harvested with or without attached leaves, were irradiated with HPS at two temperature regimes, 20°C and 200/6°C. The resulting decreases in hue angle were attributed to yellowing and not red colour formation. In conclusion, the response of apples to postharvest irradiation was affected by maturity and temperature, while pears failed to respond at all. / AFRIKAANSE OPSOMMING: Rooikleurontwikkeling van twee-kleur appels en pere verseker beter pryse vir die produsente. Na-oesbestraling om kleur te verbeter is al suksesvol uitgevoer op appels, en die doelwit van hierdie tesis was om die kondisies vir appels gedurende bestraling te optimaliseer en om die effek van bestraling op pere te evalueer. 'Cripp's Pink' appels het reageer op na-oesbestraling met hoëdruk-natriumligte (HDN) deur 'n rooi blos te ontwikkel, terwyl die reaksie op bestraling met UV-B plus gloeilamplig minder effektief was. 'Braebum' appels opgeberg by -O.5aC vir 4 of 8 weke voor bestraling het 'n afname in die kleurskakeringswaarde getoon, asook 'n toename in antosianienkonsentrasie na 72 uur se bestraling met HDN ligte. 'Forelle' pere wat dieselfde behandeling ontvang het, het geen kleurontwikkeling en geen antosianienontwikkeling getoon na bestraling nie. 'Braebum' en 'Cripp's Pink' appels wat weekliks geoes is vir 5 weke tot die optimum oesdatum is bestraal met HDN ligte. Slegs die volwasse vrugte van beide kultivars het 'n betekenisvolle toename in kleur getoon. 'Cripp's Pink' appels is geoes in twee produksie areas met verskillende mikroklimate, naamlik Ceres en Grabouw. Vrugte is opgeberg vir 0, 2 of 5 dae by -O.5aC voor bestraling vir 120 uur by of 6aC of 20aC. Vrugte van Ceres wat onmiddellik na oes bestraal is het beter kleur ontwikkel by 6aC as by 20aC. Kleurontwikkeling by vrugte bestraal by 6 of 20aC het nie verskil wanneer vrugte vooraf opgeberg was by -~5ac vir 5 dae nie. Vrugte van Grabouw het konstant beter kleur pntwikkel wanneer bestraling by 6°C eerder as 20°C plaasgevind het. In die volgende eksperiment, was beide die vrugte van Ceres en Grabouw vir 20 dae opgeberg by -o.soC voor bestraling by 6°C of 6°/20°C. Die flukturerende temperatuur regime het afnames van 70° en 65° in kleurskakeringswaarde getoon vir die vrugte van Grabouw en Ceres, respektiewelik. Die afname was kleiner (±200)wanneer vrugte by 6°C bestraal is. 'Cripp's Pink' appels wat goed gekleur was en opgeberg is by 3rC terwyl dit blootgestel is aan HDN ligte vir 144 uur, het 'n toename van 29.30 tot 48.3° getoon vir die kleurskakeringswaarde, en antosianienkonsentrasie het afgeneem van 739 I'g.g-1 tot 283.6 I1g.g-1. Die kontrole vrugte opgeberg by dieselfde temperatuur in die donker het geen verandering in beide die kleurskakeringswaarde of die antosianienkonsentrasie getoon nie. 'Bon Rouge' en 'Red d' Anjou', twee volrooi peerkultivars, is bestraal met HDN ligte vir 72 uur en het geen betekenisvolle verandering in kleur getoon nie. 'Forelle' pere, geoes met of sonder 'n aangehegte stingelsegment, is bestraal met HDN ligte by twee verskillende temperatuur regimes, nl. 20°C of 20/6°C. Die afname in kleurskakeringswaarde is aan vergeling toegeskryf eerder as aan rooikleurontwikkeling. Ter opsomming, die reaksie van appels op na-oes bestraling is beïnvloed deur rypheid en temperatuur, terwyl pere geen reaksie getoon het nie.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric) Food Sience and Technology)--University of Pretoria, 2005. / Food Science / unrestricted

Read the abstract in the section 00front of this document. / Thesis (PhD (Plant Pathology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

No description available.

Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2017 / Tomato is popularly consumed as fresh vegetable or processed product due to its nutritional and health benefits. However, due to its high perishability, tomato cannot be stored for longer duration. Therefore, the aim of this study was the determination of appropriate dipping times into different calcium chloride concentrations to preserve the postharvest quality, storage and the shelf-life of tomato fruit. 'Classic round' tomato fruit were harvested at their pink maturity stage. The experiment was carried out as a completely randomized design (CRD), factorial arranged as 4 × 3 × 8. Treatment factors were: 4 × CaCl2 (0, 0.0045, 0.01 and 0.03%), 3 × dipping times (0, 30 and 60 minutes) and 8 × shelf-life (0 - 7 days). Fruit were stored at 15⁰ C for 30 days, thereafter, held under room temperature for 0 - 7 days of shelf-life while collecting data. During shelf-life period, fruit were evaluated for weight loss, firmness, colour, TSS, TA, pH, physiological and pathological disorders. The interaction between the treatments and dipping times showed a significant effect on weight loss, firmness, colour parameters [L*, b*, chroma and hue angle (⁰)], total soluble solids (TSS), titratable acidity (TA), pH, decay and black mould occurrence. However, significant interactive effects were not shown on a* colour component and chilling injury. In conclusion, calcium chloride (CaCl2) improved the quality and shelf-life of 'Classic round' tomato fruit. Calcium chloride concentration 0.01% was effective at 30 minutes dipping time, meanwhile, 0.03% CaCl2 was effective at 60 minutes dipping time. Therefore, 0.01 and 0.03% can be recommended for commercial preservation use for tomato fruit quality and shelf-life. / Agricultural Research Council-Tropical and Subtropical Crops (ARC-TSC) and National Research Foundation (NRF)

‘Fuerte’ makes up 25% of the avocados exported from South Africa to European markets and requires shipping periods of up to 28 days and a correctly managed cold chain. A temperature of 5.5°C and expensive CA and 1-MCP treatments are currently used to delay ripening over this lengthy cold chain; however, fruit still appear on the European market showing signs of softening and physiological disorders. Increased competition on the global market and the disadvantage of a particularly long distance to the European market has challenged the South African export industry. These challenges have necessitated improved road and sea transport logistics, co-ordination with producing countries which supply fruit to European markets over similar periods as South Africa, and research into ultra-low temperature storage to possibly enable future access to new lucrative markets in the USA, China and Japan. It is also known that there are various ‘weak links’ in this cold chain and that cold chain breaks are detrimental to fruit quality, but further research into the negative effects of these cold chain breaks at ultra-low temperatures was needed. Thus, the objective of the study was to determine the potential for shipping ‘Fuerte’ avocados at temperatures of 2°C as well as determining the effects of cold chain breaks on fruit quality, throughout the growing season and possibly for an extended period of 56 days. ‘Fuerte’ avocados were harvested at three different maturity stages reflecting early-, mid- and late-season fruit, with moisture contents of 74%, 68% and 63%, respectively. Fruit were stored at 2°C or 5.5°C, treated with 1-MCP and waxed. Additionally cold chain breaks (24 hour delay and break at 14 days) were implemented. Fruit softening, mass loss, days-to-ripening, external and internal quality as well as antioxidant levels and total sugar levels were determined. The first aim was to determine whether a lower than currently used storage temperature could be a successful alternative to 1-MCP use. A storage temperature of 2°C provided good internal quality as well as reduced mass loss and fruit softening, which is related to the slightly reduced use of C7 sugars at 2°C compared with 5.5°C. Although the overall occurrence of external chilling injury was relatively low, 2°C storage caused a notably higher occurrence of external chilling injury than 5.5°C storage, particularly early in the season, but extended the days-to-ripening. Unfortunately, no correlation between the anti-oxidants in the exocarp and external damage was found. Waxing significantly reduced the external damage on fruit stored at 2°C, so much so, that the treatment combinations of ‘2°C, no 1-MCP, waxed’ showed no external chilling injury throughout the season. Further, waxing fruit at 2°C could eliminate the need for 1-MCP, delivering a product of the required shelf-life and quality. Best results were achieved for mid-season fruit stored at 2°C. Late-season fruit would potentially be the most profitable to store at this low temperature, however, body rots (anthracnose and stem-end rot) were more common in the late-season. Storage at 2°C can therefore maintain the internal quality over a storage period of 28 days and be a potential alternative to 1-MCP use as the season progresses. The effect of cold chain breaks on fruit quality was then investigated and showed that both a delay and a break in the cold chain increased mass loss and fruit softening, reduced days-to-ripening and increased external chilling injury, especially early in the season. Water loss was the main contributor to the decreased fruit quality which resulted from the delay in cooling, increasing external damage significantly, particularly early in the season. The break at 14 days had a marked effect on physiological activity of fruit during storage, seen mainly in the increased metabolic activity, resulting in increased fruit softening and water loss during storage and a decrease in C7 sugars and thus shelf-life, particularly for fruit stored at 5.5°C. Importantly, 1-MCP use and storage at 2°C reduced the effects of cold chain breaks with respect to fruit softening, however, lowering the storage temperature had a greater negating effect than 1-MCP and could be a successful alternative to the use of 1-MCP. The internal quality throughout the experiment was very good, with few internal disorders and no significant treatment effects on internal quality and C7 sugar concentrations. Overall, a break in the cold chain, before and during cold storage, resulted in a marked reduction in fruit quality. The storage temperature of 5.5°C should not be used for a 56 day storage period as it resulted in significant fruit softening during storage, even when 1-MCP was used, and resulted in significantly more external chilling injury in the mid- and late-season than at 2°C. Storage of 1-MCP treated, waxed fruit at 2°C, resulted in the best shelf-life and fruit quality, particularly mid-season fruit which had negligible external chilling injury and 100% sound fruit. Early-season fruit suffered significant external chilling injury at 2°C and late-season fruit had the highest body-rots and internal disorders at this storage temperature. Although mid-season fruit could be successfully stored at 2°C for 56 days, the use of a 56 day storage period is not recommended as a practical storage period, due to the high risk of external damage, particularly if maturity levels are not optimum and trees and fruit are not of the highest quality. Overall this thesis has shown that 1-MCP treatment can play an important role early in the season when fruit are susceptible to external damage, however, storage at 2°C results in good quality fruit and, when used in conjunction with waxing, appears to be a viable alternative to the use of 1-MCP, particularly later in the season. Further, the negative effects of cold chain breaks on fruit quality have been demonstrated and, importantly, the storage temperature of 2°C negates the fruit softening effects of these breaks, even if 1-MCP is not used. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Avocados are one of the major food sources in tropical and subtropical regions and are an important horticultural crop in South Africa. Avocados are exported over long distances and may have storage times of up to 30 or more days at temperatures of about 5.5oC. This procedure increases the risk of poor fruit quality, including physiological disorders, early softening and postharvest disease incidence. A major component of the postharvest diseases is Anthracnose caused by Colletotrichum gloeosporioides. Anthracnose infects unripe fruit and once infected, the fungus remains dormant in the fruit until ripening begins. This leads to a problem for producers and packers, as the presence of the disease cannot be detected on the pack line, and fruit is not removed. Anthracnose control is normally done through pre-harvest treatment with copper-based fungicides. While effective such treatment needs to be repeated frequently, resulting in copper residues on the avocados. The study was conducted to investigate the effects of phosphoric acid and potassium silicate on known antifungal compounds and critical enzymes of the pathways elemental for systemic resistance inducers, so as to evaluate the potential for using them as alternatives to or in conjunction with, copper fungicides in the control of Anthracnose in avocado fruit. The study included storage temperature and time variations, to take account of the logistics in shipping avocado fruit to distant markets. Pre- and postharvest applications of phosphoric acid and potassium silicate were used, and after harvest, fruit were either ripened at room temperature (22oC) without storage or stored for 28 days at temperatures of 5.5oC or 2oC before analysis. Concentrations of phenolics, activity of the enzyme phenylalanine ammonia lyase (PAL) and a known antifungal diene were determined in the fruit exocarp. Pre-harvest treatments of phosphoric acid showed that the highest phenolic concentration was found in fruit harvested 14 days after application for fruit stored at room temperature. For fruit stored at 5.5°C it was seen that as fruit softened, phenolic concentrations increased compared with hard fruit immediately after storage, with the highest increase noted for fruit harvested 7 days after application. When comparing the three storage temperatures, phenolic concentrations were enhanced most when fruit was stored at 2°C. Postharvest treatments showed a significant increase in phenolic concentrations for potassium silicate treated fruit stored at room temperature and 2°C when determined immediately after storage. Fruit stored at 5.5°C showed an increase in phenolic concentrations as it became softer. When considering PAL enzyme activity, it was found that postharvest treatments of both potassium silicate and phosphoric acid influenced enzyme activity, with potassium silicate having greater effects. Similarly, an increase in PAL activity was noted in the pre-harvest phosphoric acid treatment harvested 14 days after application for fruit ripened immediately as well as fruit stored at 5.5°C. Fruit stored at 2°C showed the highest PAL activity for fruit harvested 7 days after application. No results were obtained in the analysis of antifungal compounds for both pre- and postharvest treatments. However, it is suggested that the antifungal diene could follow similar trends to those found for phenolics. It is concluded that applications of both phosphoric acid and potassium silicate do create changes in phenolic concentrations and the activity of the enzyme PAL which is involved in the synthesis of phenolic compounds known to possess antifungal properties. It is therefore possible that phosphoric acid and potassium silicate may be used as part of an integrated programme for Anthracnose control, and should be tested as potential alternatives for high volume copper-based fungicides. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Grape quality is important for the producer, exporter and the consumer. Consumers judge table grapes according to their size, colour, taste and shelf life. The consumer’s prerequisites will influence the producer. Therefore, it is essential to know how the table grape berry develops so that it can be manipulated, favouring the postharvest quality and shelf life. This study was performed on Prime and Crimson Seedless, both grafted onto Ramsey, in the Paarl district of South Africa. The aim of this study was to describe and quantify table grape berry development and compositional changes taking place throughout growth and ripening. The effect of sugar:acid ratio on postharvest shelf life was also evaluated. To evaluate whether berry size influenced the measured development parameters, three berry sizes were induced for both cultivars by using plant bioregulators such as gibberellic acid (GA3) and forchlorfenuron – synthetic cytokinin (CPPU) or girdling. The following sizes were obtained for Prime: (i) small berries (<20 mm) with no treatment, which acted as the control; (ii) medium berries (20-24 mm) obtained by 15 ppm GA3 application at 8 mm berry size; (iii) large berries (>24 mm) obtained by combination of 15 ppm GA3 and 1 ppm CPPU application at 8 mm berry size. Crimson Seedless berry sizes were as follows: (i) small berries (<18 mm) with no treatment, which acted as the control; (ii) medium berries (18-22 mm) treated with 10 ppm GA3 at 7 mm berry size; (iii) large berries (>22 mm) treated with 10 ppm GA3 and vines were girdled at 7 mm berry size. To evaluate the effect of sugar:acid ratio on postharvest shelf life, grapes were stored for five weeks at -0.5 ˚C and another week at 7.5˚C. The bunches were evaluated for loose berries, browning, soft tissue breakdown, decay and berry split. The following components were analysed for both cultivars to determine changes in berry composition throughout the season: berry fresh weight, total soluble solids (TSS), glucose, fructose, titratable acidity (TA), tartaric acid, malic acid, abscisic acid (ABA) and total phenols. Total and individual anthocyanins were analysed for Crimson Seedless. Differences were obtained for the three berry sizes for both cultivars. Véraison, representing the start of ripening, started at the same time in successive seasons: 21 days after pea size berry (5 mm berry diameter) for Prime and 28 days after pea size berry (5 mm berry diameter) for Crimson Seedless. A lag stage was not observed, at seven day sampling intervals, for either of the cultivars. Components such as TSS, glucose, fructose and TA content per berry were influenced by berry size in either one or in both seasons for both cultivars. Significant changes in component concentration were detected at the start of, or around véraison. Sugar concentrations (TSS) already started to increase for both cultivars before the start of véraison. At véraison, concentrations of glucose, fructose and ABA increased while concentrations of TA, tartaric acid, malic acid and total phenols decreased. Total anthocyanins in Crimson Seedless started to increase one week after véraison commenced. The main anthocyanin found in Crimson Seedless was peonidin-3-glucoside. During ripening a 1:1 glucose:fructose ratio was detected in both cultivars. Prime tartaric:malic acid ratio was lower than Crimson Seedless tartaric:malic acid ratio in both seasons. Tartaric acid was the main organic acid found in Prime, while malic acid was the main organic acid found in Crimson Seedless. No significant differences were found in the postharvest defects between the different berry sizes. However, tendencies for differences were observed which led to the assumption that medium size berries were more prone to loose berries in both cultivars. Large berries showed a higher percentage berry split for both cultivars. Crimson Seedless second harvest date took place 24 hours after rainfall which could have very likely led to the higher percentages berry defects compared to the first season. Greater berry decay was found with later harvest dates for both cultivars. No significant differences were found for the TSS:TA ratio between the three berry sizes for both cultivars. Postharvest defects were therefore found not only to be influenced by TSS:TA ratio but rather by harvest date and packing procedures. Environmental conditions prior to harvest also had an impact on postharvest shelf life. / AFRIKAANSE OPSOMMING: Druif kwaliteit is belangrik vir die produsent, uitvoerder en verbruiker. Tafeldruiwe word gekeur deur die verbruiker volgens grootte, kleur, smaak en raklewe. Die verbruiker se voorkeure sal dus die produsent beïnvloed. Daarom is dit belangrik om te weet hoe tafeldruiwe ontwikkel ten einde korrelsamestelling te manipuleer om na-oes kwaliteit en raklewe te kan bevoordeel. Hierdie studie is uitgevoer op Prime en Crimson Seedless, beide geënt op Ramsey, in die Paarl distrik van Suid Afrika. Die doel van die studie is om vas te stel hoe korrelsamestelling gedurende groei en rypwording verander. Die effek van suiker:suurverhouding op na-oes raklewe is ook geëvalueer. Om te kan meet of korrel grootte die gemete parameter beïnvloed is drie korrelgroottes verkry vir albei kultivars deur die gebruik van plant bioreguleerders, te wete gibbereliensuur (GA3) en sintetiese sitokiniene (CPPU), of ringelering. Die volgende korrelgroottes is verkry vir Prime: (i) klein korrels (<20 mm) d.m.v. geen behandeling, geklassifiseerd as kontrole; (ii) medium korrels (20-24 mm) d.m.v. ‘n 15 dpm GA3 behandeling by 8 mm korrelgrootte; (iii) groot korrels (>24 mm) d.m.v. ‘n kombinasie van 15 dpm GA3 en 1 dpm CPPU by 8 mm korrelgrootte. Crimson Seedless korrelgroottes was soos volg: (i) klein korrels (<18 mm) d.m.v. geen behandeling, wat as kontrole gedien het; (ii) medium korrels (18-22 mm) d.m.v. ‘n 10 dpm GA3 behandeling by 7 mm korrelgrootte; (iii) groot korrels (>22 mm) d.m.v. ‘n 10 dpm GA3 behandeling en gelyktydige ringelering by 7 mm korrelgrootte. Om die effek van suiker:suur verhouding op na-oes houvermoë te kon evalueer was druiwe gestoor vir vyf weke by -0.5˚C en ‘n verdere week by 7˚C. Die trosse is geëvalueer vir loskorrels, verbruining, sagte weefsel afbreek, verval en korrelbars. Die volgende komponente is geanaliseer vir albei kultivars om veranderinge in korrelsamestelling gedurende die seisoen te bepaal: vars korrelgewig, totale oplosbare vaste stowwe (suikerinhoud), glukose, fruktose, titreerbare sure, wynsteensuur, appelsuur, absisiensuur en totale fenole. Die totale en individuele antosianiene is ook vir Crimson Seedless gemeet. Beduidende verskille tussen die drie korrelgroottes vir albei kultivars is verkry. Deurslaan, naamlik die begin van rypwording, het op dieselfde dag in opeenvolgende seisoene plaasgevind: 21 dae na ertjiekorrel grootte (5 mm korrel deursnee) vir Prime en 28 dae na ertjiekorrel grootte (5 mm korrel deursnee) vir Crimson Seedless. In teenstelling met die tipiese korrel ontwikkelingspatroon is ‘n rusfase nie waargeneem by beide kultivars nie. Komponente soos suikerinhoud, glukose, fruktose en titreerbare suur inhoud per korrel is deur korrelgrootte beïnvloed in een of albei seisoene vir beide kultivars. Suiker konsentrasie van albei kultivars het reeds voor deurslaan begin toeneem. By deurslaan het die konsentrasies van glukose, fruktose en absisiensuur inhoud toegeneem, terwyl die konsentraies van titreerbare sure, wynsteensuur, appelsuur en totale fenole gedaal het. Totale antosianiene in Crimson Seedless het ‘n week na deurslaan begin toeneem. Die hoof antosianien in Crimson Seedless is peonidien-3-glukosied. Gedurende rypwording was daar ‘n 1:1 glukose:fruktose verhouding gevind vir beide kultivars. In terme van sure is Prime se wynsteensuur:appelsuur verhouding laer as in Crimson Seedless vir albei seisoene. Wynsteensuur is die hoof organiese suur in Prime terwyl appelsuur die hoof organiese suur in Crimson Seedless is. Geen betekenisvolle verskille vir na-oes houvermoë tussen korrelgroottes is waargeneem vir beide kultivars nie. Daar was egter tendense wat aanleiding gegee het in die aanname dat medium grootte korrels geneig is tot loskorrels in albei kultivars. Groot korrels het ‘n hoër korrelbars persentasie getoon vir beide kultivars. Crimson Seedless se tweede oes het plaasgevind 24 uur na reënval, wat aanleiding gegee het tot hoër persentasies korrelbederf. Hoër persentasie korrelbederf was ook gevind met later oesdatums. Geen beduidende verskille is gevind vir suiker:suur verhouding tussen die drie korrelgroottes vir beide kultivars nie. Dus word na-oes houvermoë nie net deur suiker:suur verhouding beïnvloed nie, maar ook deur oestyd en verpakkingsprodsedures. Omgewingsomstandighede voor oes kan ook na-oes houvermoë beïnvloed.

Doctor of Philosophy (PhD) / The Flesh Browning (FB) disorder of ‘Cripps Pink’ apples presents a significant threat to the established market identity of the ‘Cripps Pink’ apple in Australian and export markets. Climatic conditions during fruit growth and development predispose ‘Cripps Pink’ apples to developing the FB disorder during storage. The FB disorder can be classified into two distinct disorders based on their physiological and structural differences and by seasonal climatic conditions. The diffuse type of FB (DFB) is a chilling injury, occurring in districts or seasons accumulating less than 1100 growing degree days (GDD) above 10oC between full bloom and harvest. In these climatic conditions, ‘Cripps Pink’ apples have delayed postharvest ethylene production. Diffuse FB effects fruit cortex tissue and is characterised as cellular collapse. Storing fruit at 3oC can reduce the incidence of DFB. The radial type of FB (RFB) is primarily a senescent disorder, occurring in districts or seasons accumulating greater than 1400 GDD above 10oC between full bloom and harvest. In these climatic conditions, postharvest ethylene production is not delayed. Radial FB affects the cells adjacent to the vascular tissue of the fruit and is characterised by damaged cell walls. Storing fruit at 1oC can reduce the incidence of RFB. Harvest maturity and the level of CO2 in the storage atmosphere are additive influences on the development of RFB. Seasons or districts accumulating more than 1700 GDD have a very low risk for developing RFB. Seasonal climatic conditions can provide a guide for predicting the risk of developing RFB and DFB during storage.