Doctoral Degrees (Horticulture)

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Browsing Doctoral Degrees (Horticulture) by browse.metadata.advisor "Crouch, Ian"

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    Alternative postharvest technologies for the maintenance of ‘Parthenon’ broccoli quality during export and domestic marketing.
    (Stellenbosch : Stellenbosch University, 2022-04) De Beer, Tarryn; Crouch, E. M.; Crouch, Ian; Theron, K. I.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Broccoli is prized for its nutritional quality. The green colour and a compact head symbolise freshness. Export and domestic marketing of broccoli is limited by its high perishability. The aim of this study was to investigate the use of two 1-methylcyclopropene (1-MCP) application methods in combination with packing to maximise broccoli storage life under different temperature regimes typically found in the export and domestic handling chains. Under simulation of domestic handling chains, optimal temperature storage (0 °C) of broccoli (cv. Parthenon) in combination with 1-MCP and packaging [Xtend™ modified atmosphere packaging (MAP) or macro-perforated high-density polyethylene (HDPE) liners] resulted in a maximum storage duration of 30 days. In a second season, optimal temperature storage with MAP (RipeLock™) allowed for 42 days storage. Storage at suboptimal temperatures (viz. 7.5 °C or 12 °C), in mixed loads with ethylene is, however, common during domestic handling. Under such environments 1-MCP prevented broccoli (cv. Parthenon) yellowing that occurred with increasing storage temperature from 0 °C-7.5 °C and 7.5 °C-12 °C. Furthermore, 1-MCP alone or in the presence of ethylene extended shelf-life of broccoli (cv. Parthenon) compared to controls, at both temperatures. This research showed how an in-box treatment system of 1-MCP can be used as a viable alternative to the traditional, bulk, in-room application method, having a similar effect in reducing yellowing compared to controls. Sensory quality of broccoli was maintained in MAP (RipeLock™) at 0 °C and 7.5 °C. At 12 °C, where sensory quality was the poorest, 1-MCP reduced the perception of ‘sulphur odour’ compared to untreated and ethylene exposed broccoli. Dimethyl trisulphide (DMTS), an off-odour related volatile, was the most abundant volatile measured at all storage temperatures. The oxidative state of broccoli increased with an increase in storage temperature from 0 °C to 7.5 °C to 12 °C. Ascorbic acid and glutathione were oxidized with an increase in storge temperature. Glutathione, however, had a consistently higher percentage oxidation compared to ascorbic acid. Under simulated export conditions, broccoli was stored at 0 °C in various MAP types with or without 1-MCP. 1-MCP was either applied in-room before packaging or in-box during packaging. Results showed that extended storage without packaging is not recommended due to excessive weight loss. Across two seasons variations in shelf-life were noted. In the first season, a maximum storage duration of 25 days was realised with broccoli stored in Xtend™, or a generic HDPE MAP film with 1-MCP. In the second season, the maximum storage duration was 35 days, irrespective of MAP type or 1-MCP treatment. Here, the limiting factor for shelf-life was sensory quality. At optimal temperature volatiles related to off-odour were negligible, indicating that sensory deterioration was not related to fermentation in the MAP environment. In the second season it was reported that if good quality broccoli is stored at 0 °C, RipeLock™ or Xtend™ MAP in combination with 1-MCP should yield no benefit over untreated broccoli in non-specific, generic liners bags (15 μm HDPE).
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    Browning and watercore disorders in 'Fuji' apples explored by means of X-ray computed tomography (CT)
    (Stellenbosch : Stellenbosch University, 2020-12) Chigwaya, Kenias; Crouch, E. M.; Crouch, Ian; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The Fuji apple cultivar occupies 9% of land under apple production in South Africa. To ensure all year-round fruit availability, ‘Fuji’ apples are stored for extended durations. However, ‘Fuji’ apples are prone to internal browning (IB) during storage. IB is characterized by patches of brown flesh in the apple tissue, which makes fruit unmarketable and causes financial losses. Browning symptoms that have been identified in apple cultivars include radial browning, diffuse browning, combination browning, CO2 damage and core-flush. Techniques such as X-ray computed tomography (CT) that can evaluate IB disorders non-destructively are important. This study aimed to explore IB types and watercore in ‘Fuji’ apples quantitatively and qualitatively using X-ray CT. Exposure of fruit to high CO2 conditions for 3 days after harvest at 21 °C induced IB in the core region of fruit. The construction of porosity maps for intact fruit enabled characterization of tissue structure before and after disorder development. Porosity distribution of ‘Fuji’ was higher in the cortex region compared to the core region. High-resolution X-ray CT scans performed on IB affected and unaffected fruit tissue showed differences in microstructural properties such as porosity, pore size distribution and pore connectivity. Fruit size had a significant effect on the susceptibility of ‘Fuji’ apples to CO2 stress-induced IB. Radial porosity profiles did not differ significantly between fruit that developed IB and fruit that did not develop IB. However, porosity along the axial profile was generally higher for fruit that did not develop IB, particularly in the region between the calyx end and the core region. This was the first X-ray CT study carried out on South African ‘Fuji’ apples to evaluate how fruit microstructural properties relate to the IB types identified under different storage conditions. A further study was done to determine microstructural properties of watercore affected fruit tissue and the effects on storability of ‘Fuji’ apples. X-ray CT scans showed that fruit tissue with watercore had a significantly low porosity and connectivity of pores. This may have a negative impact on respiratory gas diffusion in the fruit and could increase susceptibility to IB during storage. Furthermore, watercore affected tissue had significantly smaller cells due to plasmolysis. For long-term storage experiments, it was found that regular atmosphere (RA) stored fruit had a significantly higher incidence of core-flush compared to fruit from controlled atmosphere (CA) and delayed controlled atmosphere (delayed CA) storage. Although CA and delayed CA were effective in reducing core-flush incidence, they both resulted in a significantly higher incidence of radial browning. Fruit with CO2 damage and cavities were also evaluated in this study. CO2 damage was associated with cell damage and increased pore sphericity. All IB types evaluated resulted in an increased tissue porosity and altering of pore sphericity, anisotropy and pore size distribution. IB after short-term exposure to CO2 stress occurred only in the core region while IB types observed after long-term storage occurred in all fruit tissue regions. This study provided unique insights into the microstructural properties of different IB types occurring in ‘Fuji’ apples.