Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Shrivelling and friction discolouration (FD), as postharvest disorders, negatively influence the marketability and potential shelf life of pears. By investigating the contributing factors in each of the disorders, the potential involvement of handling and storage variables were determined. This allowed for a better understanding of the responsible factors that create susceptible environments for these disorders to occur. From the moment that pears are harvested they lose weight by means of transpiration and, to a lesser extent, respiration. When excessive losses are experienced, the fruit will appear shrivelled and the marketability and shelf life are negatively influenced. By minimizing the rates of weight loss, the occurrence of shrivelling among pears during the postharvest handling can be lessened. The periods that proved to be most conducive to shrivelling (during a simulated postharvest handling duration) were where temperatures above 0 °C were experienced. These short periods proved more perilous for shrivelling than lengthy storage durations at low temperatures. This influenced the transpiration rate in such a way that the driving force accelerated the rate of weight loss in all the cultivars that were studied. Removing field heat from fresh produce and maintaining the cold chain reduces the driving force behind the transpiration of the pears. In all the cultivars studied, ‘Packham’s Triumph’, ‘Beurrè Bosc’ and ‘Forelle’, smaller and less mature fruit were more inclined to appear shrivelled. The surface area to volume ratio is fundamental in determining the rate of weight loss. This was most evident in ‘Beurrè Bosc’. Although no reproducible results could be obtained from the morphological studies, literature has attributed this phenomenon to the composition and quantity of the cuticle layer. Reduction of weight loss was obtained by sealing of the fruit stem. This obstructed water movement from the fruit through the xylem conducting tissue to the surrounding atmosphere. Not only did the stem appear greener and fresher, but less weight loss and subsequent shrivel was noticeable in the treated fruit. This effect was most evident in ‘Packham’s Triumph’ and ‘Beurrè Bosc’, but not in ‘Forelle’. ‘Forelle’ typically has a very short, thin stem in comparison to the other two cultivars.All the cultivars showed visual shrivel symptoms after 11 days at 18 °C. Rate of weight loss was the lowest in ‘Packham’s Triumph’, but due to its prominent dimensions, it appeared shrivelled before any of the other cultivars. ‘Beurrè Bosc’ lost weight at the highest rate (0.42%.day-1). As fruit injury, in the presence of oxygen, is inevitable, the oxidative enzymatic browning of pears will always be troublesome. This defensive mechanism partially prevents the infection of the fruit where epidermal cells are injured. To minimize FD, impact and frictional forces need to be lower during both harvesting and handling practices. A laboratory scale method was developed through which reproduceable treatments could be performed, thereby subjecting the fruit to industry related friction, rather than impact, injury. By assessing the discolouration in terms of both extent and intensity, the influence of variables could be determined on both ‘Packham’s Triumph’ and ‘Doyenne du Comice’ pears. As also found in practice, ‘Doyenne du Comice’ proved to be far more susceptible to FD than ‘Packham’s Triumph’, although the activity of the enzyme, polyphenol oxidase (PPO) was found to be higher in the latter. Although no significant difference was found between the FD encountered at fruit temperature of 3 °C and 15 °C, discolouration was greater at the higher temperature. This might be attributed to a greater degree of water loss, lower cell turgidity or higher enzyme activity. Thus, fruit taken from storage and sorted directly thereafter will exhibit less FD. The contribution of condensation forming on the fruit, acting as lubrication, cannot be ignored. Such fruit, with high turgor pressure, might again be more susceptible to bruising which will only be revealed well after the injury. Since enzymes, which include PPO, catalyse biochemical reactions, the availability of sufficient substrate most probably regulates the extent of this biochemical discolouration. Harvesting at optimum maturity and preventing any unnecessary friction will most definitely reduce the occurrence of FD. The ultimate challenge remains to optimize sorting and packing conditions without compromising on fruit quality. / AFRIKAANSE OPSOMMING: Verrimpeling en friksie verbruining (FV), as na-oes defekte, het ’n negatiewe invloed op die bemarkbaarheid en potensiële raklewe van pere. Hierdie studie het die bydraende faktore vir elkeen van die defekte ondersoek. Daar is gepoog om die effek van verskillende hanteringsen opbergingsmetodes op bogenoemde defekte te bepaal. ‘n Beter begrip is verkry van die oorsaaklike faktore wat bydra tot die ontstaan van die betrokke defekte. Direk na die oes van pere, begin die vrug gewig verloor as gevolg van veral transpirasie. Oormatige verliese sal lei tot ’n vrug wat verrimpeld voorkom, met ‘n negatiewe invloed op die bemarkbaarheid en raklewe daarvan. Die voorkoms van die verrimpeling van pere tydens die na-oes hantering van die vrugte, kan verminder word deur vermindering van die tempo van gewigsverlies. Die periodes waartydens die verrimpeling veral voorgekom het, (soos gevind in ’n gesimuleerde na-oes hanteringsmodel) was wanneer temperature bo 0 °C ondervind is. Sulke kort periodes was meer geneig om aanleiding te gee tot verrimpeling as die verlengde periodes van opberging by lae temperature. Sulke periodes van hoër temperature het gelei tot versnelde transpirasie en ’n versnelde tempo van gewigsverlies in al die kultivars wat ondersoek is. Die transpirasietempo van pere kan verlaag word deur die verwydering van veld-hitte en deur die streng behoud van die koue-ketting. In al die kultivars wat ondersoek is, ‘Packham’s Triumph’, ‘Beurrè Bosc’ en ‘Forelle’, is gevind dat die kleiner en minder volwasse vrugte meer geneig was tot verrimpeling. Die oppervlak area tot volume verhouding is krities in die bepaling van die tempo van gewigsverlies. Hierdie bevinding was die prominentste in ‘Beurrè Bosc’. Alhoewel geen beduidende resultate verkry kon word van die morfologiese studies nie, is daar verskeie verwysings in die literatuur wat hierdie verskynsel toeskryf aan die samestelling en hoeveelheid van die kutikula laag. Vermindering van gewigsverlies is verkry deur verseëling van die vrugtestingel. Hierdie tegniek het gelei tot ’n blokkering van die watervloei van die vrug na die omgewing deur die xileem weefsel. Verseëling van die stingel het dit groener en varser laat voorkom, en het ook ’n merkbare vermindering in gewigsverlies en die daaropvolgende verrimpeling tot gevolg gehad. Die effek van stingel-verseëling was die prominentste in ‘Packham’s Triumph’ en‘Beurrè Bosc’. Dit was minder duidelik in ‘Forelle’ wat tipies gekenmerk word deur ‘n baie korter, dun stingel in vergelyking met die ander twee kultivars. Al die kultivars het makroskopiese verrimpeling getoon na ‘n opbergingperiode van 11 dae by 18 °C. Die tempo van gewigsverlies was die laagste in ‘Packham’s Triumph’ alhoewel dit eerste verrimpeld voorgekom het. Dit kan toegeskryf word aan die spesifieke afmetings van hierdie betrokke kultivar. ‘Beurrè Bosc’ het vinnigste gewig verloor (0.42%.dag-1). Aangesien die besering van vrugte, in die aanwesigheid van suurstof, onvermydelik is, sal oksidatiewe, ensiematiese verbruining van pere altyd problematies wees. Hierdie verdedigingsmeganisme voorkom tot ’n mate die infeksie van die vrug wanneer epidermale selle beskadig word. FV kan beperk word deur die vrugte tydens oes en hanteringsprosedures so min as moontlik bloot te stel aan impak en friksie kragte. ’n Laboratorium-model is ontwikkel ter nabootsing van die omstandighede in die industrie. Die vrugte is aan friksie, eerder as impak, onderwerp, soos ondervind in die industrie. Die omvang asook die intensiteit van die verbruining is gemeet in beide ‘Packham’s Triumph’ en ‘Doyenne du Comice’ pere. Op hierdie wyse kon die invloed van die onderskeie veranderlikes in elke kultivar bepaal word. Alhoewel die ensiematiese aktiwiteit van die polifenol oksidase ensiem (PFO) die hoogste in ‘Packham’s Triumph’ was, is gevind dat ‘Doyenne du Comice’ veel meer geneig was tot FV as ‘Packham’s Triumph’. Hierdie bevinding bevestig die verskynsel soos in die praktyk gevind. Alhoewel geen betekenisvolle verskil gevind is tussen FV by vrug temperatuur van 3 °C en 15 °C nie, was daar meer verbruining by die hoër temperatuur. Hierdie verskynsel kan toegeskryf word aan ’n groter mate van waterverlies, laer sel turgiditeit en hoër ensiem aktiwiteit. Dus sal vrugte wat direk na opberging gesorteer word, minder FV toon. Die bydrae van die kondensasie wat op die vrug vorm, en as ’n smeermiddel dien, kan nie geïgnoreer word nie. Sulke vrugte met hoër turgiditeit, mag egter meer vatbaar wees vir kneusing, wat egter eers ’n geruime tyd na die kneusing tevoorverskyn mag kom. Aangesien ensieme, wat PFO insluit, as katalis dien in biochemiese reaksies, sal die beskikbaarheid van voldoende substraat, na alle waarskynlikheid die omvang van die biochemiese verkleuring reguleer.Die oes van pere tydens optimum volwassenheid, en die voorkoming van onnodige friksie sal definitief die voorkoms van FV verminder. Die uitdaging is steeds om sortering- en verpakkingstegnieke verder te verfyn sonder om ’n negatiewe invloed op vrugtekwaliteit te hê.

Thesis (MSc (Horticulture))--University of Stellenbosch, 2006. / Rind breakdown of ‘Nules Clementine’ mandarin (Citrus reticulata Blanco) is a physiological rind disorder that develops during storage. The disorder appears following leakage of essential oil from oil glands in the flavedo, which then leaks into and oxidises the albedo. Oxidised tissue appears as brown spots in the rind. Occurrence of this disorder over the years has caused high financial losses to ‘Clementine’ mandarin producers and exporting companies. Therefore, research aimed at solving this problem was identified as a priority by the citrus industry. Several factors have been reported to be associated with rind breakdown of ‘Clementine’ mandarin fruit, and include environmental factors, fruit maturity at harvest, ethylene gas degreening, storage temperature and storage duration, canopy position where fruit are borne, plant growth regulators, and differences in susceptibility among selections. Practical information has been generated on rind breakdown, but the basic physiology of the disorder is still unresolved. The objective of this study was, therefore, to quantify the effects of various factors on the development of rind breakdown of ‘Nules Clementine’ mandarin fruit, as well as to establish an association between rind pigments and rind antioxidant capacity on the development of this disorder. In this study a series of five experiments was conducted, and included quantifying the differences in susceptibility to rind breakdown between ‘Nules’ and ‘Oroval Clementine’ mandarin fruit, investigating the effects of fruit canopy position, harvest date, ethylene gas degreening, storage temperature and duration on the development of rind breakdown. The effect of these factors on rind pigments and antioxidant capacity was also reported. Generally, ‘Nules’ and ‘Oroval Clementine’ mandarin fruit exhibited similar characteristics at harvest, in terms of maturity and antioxidant capacity. After storage, ‘Nules Clementine’ mandarin developed higher levels of rind breakdown than ‘Oroval Clementine’ mandarin. However, the difference in susceptibility to rind breakdown of ‘Nules’ and ‘Oroval Clementine’ mandarin fruit could not be associated with the antioxidant capacity measured at harvest...

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

A market survey was conducted to determine the incidence of stem-end rot (SE) on avocado fruit obtained from the Pretoria Fresh Produce Market representing the Tzaneen production area. Dothiorella aromatica isolates collected from this survey were compared in terms of physiological characteristics i.e. growth and temperature, carbon and nitrogen utilization and pH response as well as genetic relatedness using random amplified polymorphic DNA (RAPD's). The incidence of SE was found to be as high as 31% and anthracnose 18%. Symptom development was more apparent when fruit was evaluated at the overripe than eating ripe stage. Of the 12 identified fungi isolated from SE lesions, D. aromatica was by far the most frequently isolated fungus. All D. aromatica isolates tested were found to be pathogenic using the fruit inoculation technique. Based on lesion size, isolates were separated into two groups of virulent and less virulent. Most isolates grouped within the one cluster, with only one isolate falling in the second group being less virulent. Although similar groupings were found between physiological tests, a lack of consistency as to which isolate belonged to which group was found. The optimum temperature for growth was 25°C and an initial pH of 6. The mean colony growth rate was 5 mm day-1. Isolates grew at a minimum of eight to a maximum of 27 mm within 24 hours. Isolates grew best on pectin and poorly on sorbitol when used as a carbon source. Urea supported growth best and poor growth was found on casein-amended sources. At a molecular level, the RAPD technique could be used successfully to seperate isolates into three groups based on cluster analyses. OPC02 was the most discrimatory primer and was therefore used in this study. Isolates produced DNA fragments ranging from 1500 bp to 450 bp. The results obtained from RAPDs could not be correlated with the pathogenicity and physiological tests. Future studies should focus on comparing isolates from different avocado production areas and testing different primers for the ability to distinguish between isolates of D. aromatica. / Dissertation (MInst Agrar (Plant Protection))--University of Pretoria, 2005. / Microbiology and Plant Pathology / unrestricted

Please read the abstract in the section 00front of this document / Thesis (PhD (Microbiology))--University of Pretoria, 2004. / Microbiology and Plant Pathology / unrestricted

No description available.

The problem of this investigation was to develop a satisfactory method by which insect infested corn could be treated continuously to eliminate the contamination normally found in the corn meal produced from the corn. An extensive literature review was compiled covering the processing of corn, the description of insects infesting stored corn, the sources of insect contamination, the tests for contamination in the corn meal, and the methods now employed or proposed for the reduction of this contamination. In connection with the fumigation of stored grain, tables were prepared showing the results of fumigations of grain insects with more than 400 chemical compounds. Those compounds which appeared to be best suited for this type of treatment of the corn, were then listed in a separate table and the properties of the compounds detailed so that a selection of the optimum compounds for experimental testing could be made. In addition to fumigation procedures, thermal procedures employing infrared radiation and dielectric heating were possible methods for killing the insects in the corn. Another procedure recommended for this purpose was the use of the mechanical force to kill the insect by means of high speed centrifugal machines called "Entoleter" Infestation Destroyers. By means of fragment analyses of samples of corn meal, it was found that the source of the corn and the care which it received during storage and handling were of primary importance in producing corn meal free from contamination by the present milling procedures. As a result of similar analyses it was found that precracking and aspirating of the corn on certain types of equipment prior to the normal grinding of the meal did not result in a reduction in the quantity of fragments present in the meal. Carbon tetrachloride and trichloroethylene were selected for possible utilization in very rapid fumigation of the infested corn. Laboratory apparatus based on the operation of the solvent-vapor degreaser for metal parts was constructed. In the resulting tests, it was found that with infested corn suspended in the vapor of boiling carbon tetrachloride or trichloroethylene the mortality of all stages of the rise weevil was 100 per cent after an exposure period of only one minute. Other tests indicated that after air drying of the grain the carbon tetrachloride did not have any deleterious effect on the baking properties of the corn. In connection with heat sterilization methods, tests were conducted which indicated that the baking properties of corn heated to temperatures below 160 °F were not impaired. Further tests were conducted which indicated that both infrared heating and dielectric heating were 100 per cent effective in killing all stages of rice weevil in infested com after an exposure period of two minutes to infrared radiation or one minute to dielectric heating. In both cases the temperature of the com did not reach 160 °F. Tests conducted with the "Entoleter” centrifugal machine indicated that the damage to the whole grain com by the action of the machine was excessive and all of the rise weevil were not killed. After due consideration of the experimental results it was decided that the system of rapid fumigation of the infested corn was the most reasonable solution to the problem of killing the insect infestation in the corn, The equipment necessary for the proposed system can be assembled with a few modifications of solvent-vapor, metal-degreasing equipment and with a suitable solvent recovery system. It is anticipated that the removal of the dead insects, larvae, eggs, and pupae can be accomplished on commercial milling equipment now available if the insects are killed prior to the processing and the reinfestation of the product is not an important factor during the processing. / Master of Science

The public concern over synthetic pesticides in foods and the environment has created an interest to find effective and safe non-fungicide means of controlling postharvest pathogens. The overall objective of this thesis was to evaluate the effect of potassium silicate, yeast antagonists and hot water dip treatment to control postharvest grey mould and blue mould of pome fruits, caused by Botrytis cinerea and Penicillium expansum, respectively. Botrytis cinerea and Penicillium expansum were isolated from infected strawberry and pear fruits, respectively. These isolates were found to be non-resistant to YieldPlus® (Anchor yeast, Cape Town, South Africa), a biofungicide containing a yeast Cryptococcus albidus. A total of 100 epiphytic yeast isolates were obtained from the fruit surface of “Golden Delicious” apples and “Packham’s Triumph” pears, and screened against B. cinerea and P. expansum. Fifteen yeast isolates reduced grey mould incidence by > 50%, when applied four hours before inoculation with B. cinerea. Similarly, seven yeast isolates reduced blue mould incidence by > 50%, when applied four hours before inoculation with P. expansum. YieldPlus® and yeast Isolate YP25 provided the best control of B. cinerea, while Isolate YP60 and YieldPlus® provided the best control of P. expansum on “Golden Delicious” apples. A mixture of YP25 and YP60 provided complete control of both B. cinerea and P. expansum, when applied to “Golden Delicious” apples before inoculation with either B. cinerea or P. expansum. Electron microscopy studies showed that yeast Isolates YP25 and YP60 inhibited the mycelial growth of B. cinerea and P. expansum, respectively. Preventative and curative application of potassium silicate resulted in reduced incidence of B. cinerea or P. expansum of “Golden Delicious” apples. Electron microscopy studies indicated that potassium silicate inhibited the growth of B. cinerea and P. expansum. Furthermore, treatment of “Golden Delicious” apples with either potassium chloride or potassium hydroxide resulted in reduced incidence of both B. cinerea and P. expansum. In vivo tests showed that the disease incidence of P. expansum and B. cinerea on “Golden Delicious” apples was reduced by hot water dip treatments at 58-60°C for 60 to 120 seconds, compared with the control fruit treated with sterile distilled water, without causing skin damage. The use of potassium silicate, yeasts (Isolates YP25 and YP60), YieldPlus® and the antagonists mixture (YP25+YP60) in combination, resulted in the control of B. cinerea and P. expansum of “Golden Delicious” apples compared with Imazalil® treated fruit. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

South African ‘Eureka’ lemon fruit must be exposed to chilling temperatures (± 0.6°C) as a mandatory quarantine treatment against insect pests for all its overseas markets. Chilling lemon fruit at such temperatures may develop chilling injury (CI) symptoms on the flavedo. This negative effect on fruit quality reduces fruit marketability. This study evaluated postharvest factors influencing physiological, biochemical and ultra-structural mechanisms involved in alleviating CI in lemon fruit. It was hypothesised that treatment with methyl jasmonate (MJ) and salicylic acid (SA) may enhance chilling tolerance in lemon fruit by maintaining cellular integrity and inducing synthesis of enzymatic and non-enzymatic antioxidants. Furthermore, fruit susceptibility to CI was associated with the source of fruit. Lemon fruit were harvested from three locations representative of moderate subtropical, warm temperate and cool subtropical environments. Harvested fruit were treated either with 10 μM MJ, 2 mM SA or 10 μM MJ plus 2 mM SA, stored either at -0.5, 2 or 4.5°C for 0, 7, 14, 21, or 28 days and afterwards transferred to 23°C for a week as shelf-life simulation. Thereafter, fruit were evaluated for alterations in physiological, biochemical and ultra-structural features involved in the manifestation of CI symptoms. Chilling damage was more severe in untreated lemon fruit than in treated lemon fruit. Storing lemon fruit at 4.5°C accelerated the manifestation of CI symptoms more so than at 2°C while storage at -0.5°C delayed the manifestation of CI symptoms. Lemon fruit of moderate subtropical origin were more chilling-tolerant than lemon fruit of warm temperate and cool subtropical origin. Treatment with 10 μM MJ plus 2 mM SA significantly (P < 0.05) improved chilling tolerance in lemon fruit. This treatment effectively maintained membrane integrity, thereby retarding electrolyte leakage and membrane lipid peroxidation as well as mass loss and respiration rate. Treatment with 10 μM MJ plus 2 mM SA was also effective in enhancing the antioxidant concentrations of vitamin E and carotenoids. The production of these antioxidants could have been part of a defence system against chilling damage, reducing CI and maintaining fruit quality. Treatment with 10 μM MJ plus 2 mM SA enhanced the concentration of compounds involved in chilling resistance, such as proline, soluble sugars, ascorbic acid and total phenolics as well as the enzyme phenylalanine ammonia-lyase (PAL). The enhancement of the defence mechanisms may have played a role in enhancing chilling tolerance in lemon fruit. The treatment also inhibited certain enzymes involved in tissue browning, such as peroxidase (POD) which might have contributed to delaying manifestation of symptoms. Polyphenol oxidase (PPO) was found to not be a good biochemical marker of the occurrence of CI. Treatment with 10 μM MJ plus 2 mM SA appeared to be able to enhance chilling tolerance in lemon fruit by maintaining the ultra-structure of the cuticle, cell wall integrity, cell membrane of parenchyma cells of the flavedo. This treatment also preserved the mineral nutrients of the flavedo (carbon, oxygen, phosphorus, potassium, calcium, magnesium, sulphur, sodium, silicon and aluminium) during cold storage. This could have played a role in protecting the fruit against chilling stress and maintaining fruit quality. Treatment with 10 μM MJ plus 2 mM SA reduced ROS production, while the activity of enzymatic antioxidants such as catalyse (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), and accumulation of essential proteins was enhanced. This increase in activity of enzymatic antioxidants and the presence of stress-responsive proteins in the lemon flavedo could have been directly involved in enhancing chilling tolerance. The CI symptoms were accompanied by an increase in membrane permeability, membrane lipid peroxidation as well as phospholipase D (PLD) and lipoxygenase (LOX) activity; however, treatment with 10 μM MJ plus 2 mM SA effectively reduced the membrane permeability, membrane lipid peroxidation, and PLD and LOX activity induced by the cold treatment. This could have contributed to the efficacy of 10 μM MJ plus 2 mM SA in inhibiting the manifestation of CI symptoms. Treatment with 10 μM MJ plus 2 mM SA enhanced flavedo total antioxidant capacity measured by ferric reducing ability of plasma; 2,2-diphenyl-1-picrylhydrazyl; 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) and the oxygen radical absorption capacity assays. The enhancement of antioxidant capacity in lemon flavedo could have contributed to the fruit’s chilling tolerance. Therefore, the effect of 10 μM MJ plus 2 mM SA treatment, enhancing chilling tolerance, may be attributed to its ability to enhance enzymatic and non-enzymatic antioxidants; activate essential proteins and mitigate the effect of ROS accumulation. With the use of 10 μM MJ plus 2 mM SA treatments, the South African citrus industry will be able to meet the quarantine temperature requirements for exportation of lemon fruit whilst reducing economic losses, depending on the preharvest conditions experienced by the fruit in each shipment. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2007. / More and more markets develop around the world for South African grapes and it becomes a challenge to store grapes for longer and reach the market with superior quality. The most destructive decay fungus, Botrytis cinerea can cause huge economic losses and successful postharvest control in the table grape industry relies on SO2. This gas not only controls the fungus but also causes losses due to phytotoxicity. SO2 also creates allergic reactions amongst certain people. In modern times the focus is on food safety and governments consequently impose certain regulations and restrictions to restrict the use of chemicals and ensure “cleaner” produce. The objective of this study was to find a steriliser to reduce B. cinerea inoculum on the berry surface prior to storage,to be used in conjunction with the current method of control – the SO2 generator pad.