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

Thesis (Ph.D. (Plant Production)) -- University of Limpopo, 2022 / In 'Hass' avocado fruit, pre-harvest and postharvest factors affecting exocarp colour change during ripening are vital to maintain the industry’s credibility, competitiveness and profitability. Currently, the South African ‘Hass’ avocado fruit exocarp colour development is affected by pre- and postharvest factors, ultimately, fruit does not develop the required purple colour during ripening. These pre- and postharvest factors must be understood in order to implement strategies that avoid downgrading of South African 'Hass' avocado fruit by lucrative markets due to insufficient purple colour development during ripening. In 'Hass' avocado fruit, exocarp colour development is associated with an increase in anthocyanin synthesis and accumulation during ripening. However, limited information is available regarding factors regulating anthocyanin synthesis and accumulation in 'Hass' avocado fruit during ripening. Therefore, the overall aims of this study were to investigate pre-harvest practices and postharvest treatment that increase exocarp anthocyanin synthesis during ripening. In addition, determine whether exocarp glucose and other antioxidants contribute to 'Hass' avocado fruit exocarp colour development during ripening. In chapter 3, the study looked at how crop load adjustment affects ‘Hass’ avocado fruit exocarp colour development during ripening at three different harvest maturities. The crop load adjustment treatments were applied as: high (100%), moderate (50%) and low (25%) at three harvest times (early, mid- and late). After harvest, fruit were stored at 5.5°C for 28 days, thereafter, ripened at 25°C. The experimental design was carried out as 3 x 3 factorial, arranged in a completely randomized design (CRD) with three replications. The results showed that total anthocyanin and cyanidin 3-O-glucoside concentrations of ‘Hass’ avocados increased following crop load adjustment from normal (100%) to moderate (50%) and low (25%) loads, resulting in improved exocarp colour development during ripening. Furthermore, we discovered that fruit harvested from moderate (50%) and low (25%) crop loads accumulated higher exocarp sugars (D-mannoheptulose and perseitol) at three harvest maturities when compared with high crop load (100%). Moreover, total phenolic concentration of fruit harvested from moderate (50%) and low (25%) crop loads was higher than that obtained from high load fruits, irrespective of harvest maturities. In chapter 4, the study examined the interaction between branch girdling and harvest maturation on the development of 'Hass' avocado fruit exocarp colour during ripening. The experimental design was carried out as 2 x 2 factorial, arranged in a completely randomized design (CRD). The results showed that fruit harvested from girdled trees had poor exocarp colour development as compared to fruit harvested from control trees, regardless of harvest time. Fruit harvested from girdled and ungirdled avocado trees did not show significant differences in visual exocarp colour during early and mid-maturity. Apart from crop load adjustment and girdling as pre-harvest methods to manipulate postharvest exocarp colour, glucose was also infused through the pedicel. Studies on the effect of glucose infusion through the pedicel on the exocarp colour of the ‘Hass’ avocado fruit during ripening were presented in chapter 5. The study included five treatments; control fruit with pedicel and infused with distilled water and glucose concentrations (0.05, 0.13 and 0.28 mM). The distilled water, glucose infused and control fruit were stored at 5.5°C for up to 28 days. After cold storage, fruit were kept at ambient temperature 25°C for ripening. The experiment was conducted as a completely randomized design (CRD) with three replications per treatment. The results showed that glucose infusion through the pedicel markedly increased anthocyanin and cyanidin 3-O-glucoside concentration during ripening. Interestingly, glucose concentrations (0.05 and 0.13 mM) resulted in purple colour development after 8 days at 25°C when compared with control, distilled water and highest concentration (0.28 mM). In chapter 6, the relationship between 'Hass' avocado fruit size, exocarp colour and related pigments with antioxidants capacity and sugar concentration during ripening were investigated. The fruit were categorized by their weight; small (< 200 g) and large (> 201 g). Their diameter and length were also measured using a vernier calliper. Fruit ware stored at 5.5°C for 28 days, then ripened at 25°C. The experimental design was carried out as a completely randomised design (CRD), using 25 fruit replications per category. The results showed that small-sized fruit developed the desirable purple to black exocarp colour when compared with large-sized fruit. Additionally, the results showed that small-sized fruit had higher antioxidant capacity as measured by 2,2 diphenyl 1 picrylhydrazyl (DPPH), ascorbic acid and flavonoid content during ripening when compared with large-sized fruit. Furthermore, it was found that small-sized fruit accumulated higher exocarp and seeds (D-mannoheptulose, perseitol, sucrose and glucose) sugar concentration. We demonstrated and concluded that exocarp colour, pigments, antioxidants and sugar concentration are closely related to size in 'Hass' avocado fruit. Knowledge from this thesis contributes toward the understanding of pre and postharvest factors that may influence colour development of ‘Hass’ avocado fruit during ripening. This study contributes towards bridging the gap in the literature on the biochemical changes associated with colour development of ‘Hass’ avocado fruit during ripening / Agricultural Research Council-Tropical and Subtropical Crops (ARC-TSC) and National Research Foundation (NRF)

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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

<p dir="ltr">The increasing consumption of fresh produce such as cantaloupes, watermelons, lettuce, and cucumbers has been linked to multiple foodborne outbreaks, highlighting the urgency of implementing effective measures to prevent bacterial contamination, colonization, and internalization. This study evaluates various antimicrobial chemical washing solutions to reduce foodborne pathogens and improve the microbial quality of fresh produce. The research investigates the impact of netting density on cantaloupe rind surfaces and assesses the efficacy of sodium hypochlorite (FAC), peracetic acid (PAA), and chlorine dioxide (ClO₂) against <i>Escherichia coli</i>, <i>Listeria monocytogenes</i>, and <i>Salmonella </i>Typhimurium. Results suggest that higher netting densities decreased the efficacy of these treatments, with smooth rind cantaloupes showing the highest bacterial reduction when treated with PAA and FAC. Further investigations into the inline application of antimicrobial washing solutions under commercial packing house conditions revealed that combining ClO₂ and PAA significantly reduced pathogen loads on cantaloupes and watermelons without adversely affecting their sensory qualities. Additionally, the study assessed the effectiveness of PAA, FAC, and accelerated hydrogen peroxide (AHP) on fresh cucumbers, broccoli, and lettuce under conditions that emulate commercial retail facilities. The treatments achieved significant log reductions in aerobic mesophilic bacteria and common pathogens, highlighting the critical role of these solutions in preventing cross-contamination during postharvest handling. Finally, the research also examined the internalization of foodborne pathogens in lettuce and cucumber plants, revealing high recovery rates of <i>E.</i><i> </i><i>coli </i>O157:O157H7 and <i>S.</i><i> </i>Typhimurium from contaminated seeds, soil, leaves, and blossoms. These findings highlight the potential for pathogen colonization and persistence in fresh produce, indicating the need for preventative agricultural practices and microbial control measures throughout the cultivation and handling processes. Together, these studies suggest that integrating effective antimicrobial washing solutions with proper storage conditions and good agricultural practices is essential for enhancing fresh produce's microbial safety and shelf-life, thereby reducing the risk of foodborne illnesses.</p>

Durante o amadurecimento ocorrem profundas alterações na composição química dos frutos e a expressão gênica desempenha papel fundamental no controle desse processo. Apesar da importância comercial do mamão, as informações a respeito da expressão gênica durante o amadurecimento são limitadas. Assim, nessa tese, técnicas de estabelecimento de perfis de RNA mensageiro, como Differential Display-PCR, cDNA-AFLP e Cross-Species Microarray, foram aplicadas para a identificação de genes com expressão alterada. Alguns genes ligados ao metabolismo e transporte de açúcares, de lipídeos e carotenóides, à degradação de parede celular e stress, e fatores de transcrição dependentes e independentes de hormônios vegetais pareceram apresentar diferenças de expressão durante o amadurecimento do mamão papaia. O isolamento dos genes diferencialmente expressos permitiu traçar um panorama da expressão gênica do fruto e, dessa maneira, a relação das funções dos genes com o amadurecimento do mamão contribuiu para o aumento do entendimento acerca da qualidade pós-colheita do fruto. / Ripening affects the quality of fleshy fruits by changing the chemical composition, and gene expression regulates most part of these transformations. Although papaya fruit is an important Brazilian crop, there are restricted studies concerning its ripening and gene expression. In this work, it is described the use of some RNA profiling techniques, such as Differential Display-PCR, cDNA-AFLP and Cross-Species Microarray, to identify ripening-related genes in papaya fruit. Using these techniques, some differentially expressed genes during papaya fruit ripening were isolated. Their functions were associated with metabolism and transport of sugars, lipids and carotenoids, cell wall disassembly, stress and transcription factors dependent and independent of plant hormones. In this way, it was proposed a pattern of gene expression during papaya fruit ripening, at least for those isolated genes, and the assemblage of these data with other authors data can locate fruit handling to a better level, minimizing postharvest losses and increasing papaya fruit shelf-life.

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.

Postharvest stem bending is one of the most detrimental factors that affect postharvest quality life of Gerbera jamesonii cutflower varieties. Stem bending is of economic importance in the cutflower industry in South Africa because it negatively affects the overall total sales. Growers and retailers want to improve the postharvest vaselife of this crop using suitable preservatives. The aim of this study was to determine suitable preservatives and optimal vaselife conditions that could prevent or minimise postharvest stem bending of Gerbera jamesonii “Black diamond”. The variety “Black diamond was selected and treated with four different floral preservative solutions. The relationship between stem bending and absorption rate of the preservative solutions was established. The data gathered indicated that there was a significant difference to the solution absorption rate and stem bending. Stem bending differed from 0 to 38 degrees. Stems treated on control, preservative 3 and 4 recorded the highest degrees of bending, while preservative 1 and 2 recorded the lowest degrees of stem bending within 12 day period. The performance results of the preservatives and control repeated three times under the same experimental conditions showed that preservative 1 and 2 can be used to minimise postharvest stem bending of Gerbera jamesonii ‘Black diamond’ / College of Agriculture and Environmental Sciences / M. Sc. (Ornamental Horticulture)

Orientador: Benedito Carlos Benedetti / Texto em português e Inglês / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-23T16:23:18Z (GMT). No. of bitstreams: 1 Teles_CesarSimas_D.pdf: 1939088 bytes, checksum: 585b37a053cde7606fc6da4a9aa803dc (MD5) Previous issue date: 2013 / Resumo: Botrytis cinerea Pers, causador da doença conhecida como mofo cinzento, é o principal problema para a conservação pós-colheita de uvas de mesa. A utilização do dióxido de enxofre (SO2) é a prática pós-colheita mais comum para o controle desta doença. Pesquisas buscam alternativas a este produto devido às reações que causa em pessoas alérgicas, danos que pode causar nos frutos e às restrições ao seu uso em sistemas de produção orgânico. Foram avaliados os efeitos da aplicação de uma atmosfera de 40% de CO2 por 24 ou 48 horas (pré-armazenagem) combinado com armazenagem em atmosfera controlada (AC) (12% O2 + 12% CO2) no controle de B. cinerea, e nos atributos de qualidade de uvas 'Flame Seedless' e 'Crimson Seedless'. Também foram avaliados, em uvas 'Crimson Seedless', e os efeitos da associação deste tratamentos com aplicações pré-colheita de cloreto de cálcio (CaCl2) ou dióxido de cloro (ClO2). Os tratamentos foram aplicados em uvas orgânicas infectadas de três formas: infectadas naturalmente, superficialmente inoculadas com conídios e inoculadas com uma baga coberta de micélio. Uvas 'Flame Seedless', naturalmente infectadas, tratadas com 40% de CO2 por 48 horas + AC apresentaram redução da podridão pós-colheita, de 22% para 0,6%, após 4 semanas, e de 100% para 7,4%, após 7 semanas. O pré-armazenamento em 40% de CO2 sozinho também limitou a incidência de mofo cinzento em frutos infectados naturalmente e em uvas inoculadas artificialmente, porém foi menos eficaz do que quando seguido pelo armazenamento em AC. A aplicação de CaCl2 ou ClO2 em pré-colheita reduziu a incidência do mofo cinzento em uvas 'Crimson Seedless' inoculadas com uma solução de conídios, porém não houve controle quando os cachos de uva foram inoculados com micélio. A aplicação de CaCl2 e ClO2 reduziram o mofo cinzento de 45% para 23,2% e 15.6%, respectivamente, em cachos inoculados com conídios e avaliados após 6 semanas armazenadas 0oC. O pré-tratamento com 40% CO2 + CA não afetou as características físico-químicas e sensoriais de uvas 'Crimson Seedless' ou 'Flame Seedless'. Em experimentos in vitro os tratamentos com 40% CO2 por 24 ou 48 h limitaram o crescimento micelial até 72 horas após o tratamento. A germinação dos conídios de B. cinerea foi retardada por 12h. Os resultados mostram que o pré-tratamento com 40% CO2 + CA possui grande potencial para ser adotado como prática comercial para conservação de uvas orgânicas / Abstract: Gray mold, caused by Botrytis cinerea Pers, is the main postharvest decay of table grapes. The use of sulfur dioxide (SO2) is the common post-harvest practice for its control. Several researchers are looking for alternative methods of control, because SO2 can cause allergic reactions, damage fruits and also it cannot be applied in organic production system. In this thesis, it was evaluated the effects of applying an atmosphere of 40% CO2 for 24 or 48 hours (pre-storage) combined with controlled atmosphere storage (CA = 12% O2 + 12% CO2) in the control of B. cinerea, and the effects in the quality and sensory attributes of 'Flame Seedless' and 'Crimson Seedless' table grapes. In addition, it was evaluated the efficacy of CaCl2 or ClO2 application in pre-harvest alone or in combination with pre-storage of 40% CO2 for 24 h + CA, to control gray mold on 'Crimson Seedless' table grapes, and the determination of the impact of these treatments on fruit quality. The treatments were applied in certified organic table grapes naturally infected, surface inoculated and nesting inoculated (inoculated with an infected berry). After 4 weeks of storage, the pre-storage in 40% CO2 for 48 hours + CA reduced postharvest rot from 22% to 0.6%, and after 7 weeks, the decay was reduced from 100% to 7.4% in 'Flame Seedless' naturally infected. The pre-storage in 40% CO2 alone also reduced the incidence of gray mold in fruits naturally infected and in artificially inoculated, but it was less effective than combined treatment. The application of CaCl2 or ClO2 pre-harvest reduced the incidence of gray mold on grapes 'Crimson Seedless' inoculated with a spore solution, but there was no control when fruits were nesting inoculated. After 6 weeks at 0oC, the application of CaCl2, and the ClO2 in fruits surface inoculated, reduced the gray mold from 45% to 23.2% and 15.6%, respectively. The pretreatment with 40% CO2 + CA did not affect quality and nor sensory attributes for both varieties tested. In vitro experiments, the treatment with 40% CO2 for 24 or 48 h limited mycelial growth for at least 72 hours after treatment. Conidial germination of B. cinerea was delayed for 12 hours. Our results showed the potential that pre-treatment with 40% CO2 associated with CA has to be adopted in commercial practice for preservation of organic grapes / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola