Browsing by Author "Chigwaya, Kenias"
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- ItemBrowning 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.
- ItemMoisture loss studies in nectarine (Prunus persica var. necterina)(Stellenbosch : Stellenbosch University, 2016-12) Chigwaya, Kenias; Theron, K. I.; De Kock, Arrie; Jooste, Mariana; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.ENGLISH ABSTRACT: Moisture loss studies in nectarines (Prunus persica var. nectarina) Moisture loss during long term storage is one of the main post-harvest problems in nectarines. The long handling chain to which fruit are exposed to, from harvest until the end of shelf-life, exposes fruit to moisture loss. Moisture loss occurs as a result of the vapour pressure deficit (VPD) between the fruit and surrounding atmosphere. In addition to causing loss of saleable weight, moisture loss also results in fruit having a shrivelled appearance. Moisture is lost from fruit through various openings in the fruit peel such as micro-cracks and lenticels. In this study we investigated the effect of fruit to fruit variation, harvest date, tree and orchard effects and cultivar differences on the variation in water vapour permeance (P’H2O) of three nectarine cultivars namely ‘Alpine’, ‘Summer Bright’ and ‘August Red’. The study showed that large fruit to fruit differences were the main contributor (>45%) to the variation in P’H2O, followed by harvest date (>35%), cultivar differences (>7%) and orchard effects (>3%) whilst tree effects did not contribute to P’H2O. Generally, the P’H2O of all three cultivars increased steadily as the harvest date approached and continued to increase post-harvest, but P’H2O at optimum harvest was not closely correlated to their susceptibility to shrivel. In addition, ‘August Red’ nectarines were exposed to different handling chains from harvest until the end of shelf-life to determine the VPD at different stages in the handling chain in order to establish the point which is most effective in reducing moisture loss and shrivel. The results indicated that none of the proposed handling chains performed better than the current standard handling protocol in reducing moisture loss and shrivel. This protocol stipulates that nectarines should be harvested during the cooler time of the day and field heat should be removed as soon as possible after harvesting. Furthermore, the handling protocol requires that nectarines should be packed within 12 hours of arrival at the pack-house. Several researchers have reported that silicon containing fertilizers improve fruit quality and we therefore also investigated whether pre-harvest applications of potassium silicate (K2SiO3) can reduce post-harvest moisture loss, shrivel and split pit in ‘Southern Glo’ nectarines. The results showed that both soil and foliar K2SiO3 applications were not effective in reducing post-harvest moisture loss, shrivel or the incidence of split pit in ‘Southern Glo’ nectarines. For future studies, it is recommended to increase the frequency of K2SiO3 applications. The study also looked at the effectiveness of different packaging films in reducing moisture loss and shrivel in ‘August Red’ and ‘Alpine’ nectarines. Failure to package fruit optimally may result in weight loss, shrivel, decay and the incidence of internal defects such as woolliness, pulpiness and over-ripeness. The results showed that the use of Xtend® and high density poly-ethylene (HDPE) bags significantly reduced moisture loss and shrivel in nectarines in both pulp trays and plastic punnets. The standard nectarine HDPE wrappers resulted in significantly higher percentage mass loss as well as shrivel incidence in ‘Alpine’ nectarines. It is therefore important to reduce moisture loss at harvest by following the standard handling protocol and by packing fruit optimally.