The influence of uniformity of heat transfer with respect to the effect of heat treatment was investigated by correlating engineering parameters with the quantified heat treatment effects. Differences in treatment effect in terms of quality, anti-pathogen and chilling injury (CI) control properties among commodities was studied by exposing them to different target temperatures. Similar effects were also evaluated and quantified within an individual commodity by a custom-designed device. This device, whose design parameters were based on a heat transfer simulation, insured that one hemisphere of a tomato was exposed to air at 39°C and 0.24 m s-1; while the other hemisphere was exposed to air at a lower temperature with a velocity of0.24 m s-1 or 0.12 m s-1. / Single-temperature heat treatment was most effective in limiting pathogen development and varied according to the parameter measured: 38°C for hypersensitive response (HR), 36°C for tissue breakdown, 36°C, 38°C or 39°C for mycelium abundance, and 38°C or 39°C for lesion size. Bilateral differences in temperature across the fruit significantly affected disease control: decreasing temperature differences significantly improved the uniformity of disease control. / Some of the effects of heat treatment on tomato quality, such as color development and resistance to CI, appear to be localized. A significant difference in redness was identified between heated parts and unheated parts of tomato fruits immediately after treatment; and the differences persisted during storage. Differences in lightness and chroma were noted on day 4. Delay in ripening caused by heat treatment was confirmed through the higher TA and TSS values of heated tomatoes or heated portion of partially heated tomatoes. / The heated parts of tomatoes showed a stronger resistance to chilling injury. The effective temperature control range for CI was wide, but temperatures higher than 39.5°C for 23 h hot air treatment could lead to adverse effects. / Differences in physiological effects between hemispheres in two chambers was reduced by directly decreasing the temperature difference between upper and lower chambers or relatively increasing the heating air flow rate, highlighting the importance of improving the uniformity of air flow around each individual treated fruit.

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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)

Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / The purpose of this study was to assess the impact of pre-harvest bagging materials on maturity indices and post-harvest quality of cherry tomatoes. At pre-harvest, fruit were bagged with blue and transparent plastic bags of 0.075- and 0.025-mm thickness, respectively. The non-bagged fruit were considered as control treatment. The experiment was carried out in a randomized complete block design arranged in a 2 × 3 factorial arrangement with three replications. Physical quality parameters such as; colour changes (L*, a*, b*, C*, h˚, and ΔE), firmness, weight loss and size were assessed. Physico-chemical parameters such as pH, total soluble solids, and total titratable acidity were also evaluated. Bagging had a significant effect on the quality of both cherry tomato cultivars. The results showed that bagging cherry tomatoes at 1.5 cm diameter with blue and transparent plastic bags accelerated maturity. Moreover, bagging with transparent plastic bags enhanced exocarp colour, reduced weight loss, retained larger size, increased pH and TTA, with an increase in TSS when compared with blue plastic bags and control, respectively at 12 days of shelf-life. In conclusion, the findings demonstrate that pre-harvest bagging has the potential to improve maturity indices and post-harvest quality of cherry tomatoes. Therefore, pre-harvest bagging can be used as an alternative method to enhance cherry tomato fruit quality and shelf-life. / NRF