Doctoral Degrees (Horticulture)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/557

Browse

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

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    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).
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    The influence of cell wall bound calcium, cell number and size on the development of mealiness in 'Forelle' pear. Evaluation of X-ray CT and NIR as non-destructive techniques for mealiness detection
    (Stellenbosch : Stellenbosch University, 2016-03) Muziri, Tavagwisa; Crouch, E. M.; Theron, K. I.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: ‘Forelle’ pear (Pyrus communis L.) is the second most planted pear and the second highest generator of foreign exchange for pears in South Africa. It is favoured for its red blush, melting texture, sweet taste and pear flavour. However, ‘Forelle’ develops mealiness, a floury, soft and dry texture with low extractable juice. Consumers dislike mealy fruit. ‘Forelle’ mealiness has been characterized by a loss of cell to cell binding during ripening in a previous study. This study aimed to further understand the role of cell wall bound and free Ca2+, as well as the cell size and cell number in the development of mealiness in ‘Forelle’. In addition, two non-destructive methods for the detection of mealiness in intact pears were examined. It was found that free Ca2+ constituted about 49-73% of the total cell Ca2+. Depending on farm origin, mealy fruit contained a lower free Ca2+ concentration compared to non-mealy pears. Plant growth regulators and selective blossom thinning that caused larger cells had a higher mealiness percentage. Scanning electron microscopy revealed larger intercellular spaces for treatments with a higher mealiness incidence. Macro X-ray computed tomography (X-ray CT) showed a higher percentage of defects in the neck of fruit that would become mealy after storage, and after softening. To our knowledge this is a first such finding. Micro (X-ray CT) found that cells of mealy fruit were larger and ellipsoidal in shape while non-mealy cells were smaller and more rounded. Mealiness was also associated with high fruit porosity. A further study described physicochemical measurements which relate to mealiness. Mealy fruit were mostly larger with a higher total soluble solids (TSS), TSS:TA ratio and lower juice area and juice weight obtained by a confined compression method. Fourier transform near-infrared absorbance spectroscopy (FT-NIR) was employed to determine if spectra could be used to distinguish between mealy and non-mealy fruit using sensory and TSS based schemes. Classification was done using orthogonal partial least squares discriminant analysis (OPLS-DA). This study showed that FT-NIR spectra can indeed be used to discriminate between mealy and non-mealy ‘Forelle’ pears. Two–class (mealy and non-mealy) discriminant analysis produced models with accuracies ranging from 51% to 95%. Mealiness caused an increase in transmittance in specific regions of the spectra. FT-NIR was then evaluated for the quantification of TSS using partial least squares (PLS) regression. Validated models had root mean squared error of prediction (RMSEP) = 0.76-0.94 and relative prediction deviation (RPD) = 1.53-2.17, with the equator blush consistently giving better performance for three farms making the model ideal for hand held FT-NIR applications. External validation results of farm location showed reduced model robustness. The decrease in prediction performance was attributed to the differing TSS ranges in locations and possibly seasons. It is recommended that future studies on FT-NIRs calibration models for ‘Forelle’ use fruit from wide origins with wide TSS ranges over various seasons.
  • Thumbnail Image
    Item
    The potential of dynamic controlled atmospheres and possible mechanisms in mitigating superficial scald in Apples cv. ‘Granny Smith’
    (Stellenbosch : Stellenbosch University, 2015-12) Mditshwa, Asanda; Opara, Umezuruike Linus; Crouch, E. M.; Vries, Filicity Ann; Van der Merwe, Jacobus; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The development of a postharvest method for controlling superficial scald, maintaining quality and reducing postharvest losses of ‘Granny Smith’ apples is essential in maintaining the competitiveness of the South African apple industry. Previously, the South African apple industry relied on diphenylamine (DPA) for controlling scald disorder; however, increasing consumer concerns and reductions in maximum residue levels (MRLs) have highlighted the urgent need for alternative control strategies. Currently, there is no effective non-chemical method for controlling superficial scald for South African apple producers. The overall aims of this study were (a) to examine the potential of dynamic controlled atmospheres (DCA) in controlling superficial scald in apples, and (b) to investigate the mechanism of action of DCA in controlling scald, should it be effective. To get a deeper understanding of superficial scald etiology and physiological dynamics of apples, studies in paper 2 and 3 were conducted. In paper 2, studies on antioxidants contents and phytochemical properties of apples harvested at pre-optimal and optimal maturity were conducted. Significant increases in fruit antioxidant capacity and ascorbic acid concentration occurred with increasing maturity. Fruit harvested at optimal maturity had lower total phenolic contents compared to pre-optimal maturity. Phenolic compounds including catechin and quercetin were also higher in pre-optimal compared to optimal maturity. In paper 3, an attempt was made to classify apples with different levels of scald severity based on metabolomics analysis. The results showed that ethylene, α- farnesene, 6-methyl-5-hepten-2-one (MHO) and reactive oxygen species (ROS) increased with scald severity but declined in severely scalded fruit. Discriminant analysis successfully classified fruit based on scald severity. Ethylene, ROS and lipid peroxidation were identified as the major contributors in separating the five scald severity levels studied. Studies in paper 4 focused on whether DCA is effective in controlling superficial scald. The minimum period for the exposure of fruit to DCA before an extended shipment period of 10 weeks was also investigated. The results showed that DCA was highly effective in controlling scald for both pre-optimal and optimal harvested fruit. The results further demonstrated that DCA stored fruit can be shipped for 6 weeks; however, extending the shipping period up to 10 weeks might lead scald development and undesired fruit quality. Fruit stored in DCA before shipment generally had higher flesh firmness and ground colour. It was also shown that DCA inhibit scald by retarding the accumulation of scald-associated metabolites such as α-farnesene and MHO. Paper 5 focused on the impact of DCA on ROS, antioxidant capacity and phytochemical properties of stored apples. Using principal component analysis, two clusters which could be identified as DCA and RA stored fruit were noticed. Compared to RA stored fruit associated with higher ROS and lipid peroxidation, fruit stored at DCA was characterized by higher contents of ascorbic acid, total phenolics and antioxidant pool. The research reported in paper 6 investigated the efficacy of repeated application of DCA on apples with high scald potential. During the marketing season, an unexpected demand of fruit often leads to the opening and resealing of storage chambers. Thus, the efficacy of a repeated DCA treatment after an interruption period at RA was investigated. Fruit were stored for up to 16 weeks in DCA with a 14 d interruption in RA at -0.5 °C, 95% RH. The results showed that efficacy of DCA was not significantly affected by the interruption. However, the development of 1% scald after 4 months of storage could be an economic setback for fruit producers. In paper 7, the influence of DCA on aroma volatiles was assessed. DCA stored fruit had significantly lower total amount of volatiles detected compared to fruit stored in RA. Notably, the production of 1-butanol, 1-hexanol and 1-hexenol by fruit stored in DCA were only 42%, 38% and 39%, respectively, of the amounts detected in the RA. The known characteristic flavour of ‘Granny Smith’ apples was attributed to the production of ethyl-2-methylbutyrate, ethyl hexanoate and hexyl acetate. The contribution of these three aroma volatiles was higher with increasing storage duration. In paper 8, the research identified effective variables that could be used to develop prediction models for superficial scald incidence in harvested ‘Granny Smith’ apples. Stepwise multiple regression found MHO, antioxidant capacity (FRAP), ascorbic acid and lipid peroxidation to be the best combination of predictive variables for scald. After validation, this combination gave a good prediction of scald incidence (R2 = 0.94). The identified variables proved to be effective regardless of fruit maturity status. The results from this thesis provide an alternative non-chemical postharvest technology for the South African apple industry. The study further provides insights on the mechanism of action of DCA in controlling scald and maintaining fruit postharvest quality of ‘Granny Smith’ apples. Overall, the results contained in this thesis will be very instrumental in future optimisation of DCA technology in the apple industry, and provides a valuable guide for improved the storage of apples susceptible to superficial scald.