Department of Horticulture

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Browsing Department of Horticulture by browse.metadata.advisor "Botes, A."

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    Feasibility of closed ventilation and automatic ventilation for sea freight of Proteaceae cut flower stems
    (Stellenbosch : Stellenbosch University, 2018-03) Matsikidze, Stenford Ngonidzashe; Hoffman, L. (Lynn) (Horticulturalist); Huysamer, M.; Botes, A.; Stllenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Global trends aimed at advancing sea freight technology and reducing carbon emissions have led to the invention of automated reefer technologies. This development brings the challenge of having to determine product physiological limits that are vital for the implementation of automatic ventilation technology on South African produced Proteaceae cut flower stems. A study was conducted to determine the respiration rates, lower O2 limits and CO2 toxicity tolerance limits of Proteaceae cut stems in order to assess the feasibility of using automatic ventilation (AV+) vs. conventional fixed open-air exchange (AirEx) ventilation shipping of Proteaceae cut stems. In a closed ventilation system (representing unvented conditions as is possible with AV+ technology) which contained a mixed load of Proteaceae products in 45-55 % free air, it was observed that the O2 level fell to approximately 8.5 % whilst the CO2 level rose to about 10 %, when a HarvestWatch™ dynamic controlled atmosphere (DCA) system was used for gas sampling. Using a handheld gas analyser as an alternative sampling method revealed that under these conditions O2 levels fell below 2 %, and CO2 levels rose to above 17 %. Although the O2 dropped considerably, it was still above the Lower Oxygen Limit (LOL), which ranged from 0.09-0.33 % O2, 0.08-0.41 % O2 and 0.08-0.48 % O2 for Leucadendron, Leucospermum and Protea products respectively. At 5 ℃, the respiration rates were between 15.11-48.07 mL CO2.kg-1.h-1 for Leucadendron, 19.06-45.44 mL CO2.kg-1.h-1 for Leucospermum and 10.76-27.24 mL CO2.kg-1.h-1 for Protea. Closed ventilation, low O2 and high CO2 atmospheres generally resulted in mass loss that was lower than or comparable to AirEx. The inflorescence and leaf colour changes in Proteaceae products stored in closed ventilation, low O2 and high CO2 treatments were commercially not significant. There were no signs of low O2 and/or high CO2 damage on the stems stored under closed ventilation. The inflorescence and leaf visual quality of Proteaceae products stored in closed ventilation was generally better than that of stems stored in AirEx. Leucadendron, Leucospermum and Protea stems stored in high CO2 treatments had comparable or better quality than stems stored in AirEx. However, exposure to 15 % CO2 for 21 d reduced longevity of some products. In Leucadendron, the response to AirEx, DCA and 2 % O2 on flower head visual quality was variable and the treatments were equally effective in maintaining leaf visual quality. Flower and leaf visual quality and longevity was comparable between the AirEx and low O2 treatments in Leucospermum and Protea. Monosaccharides plus oligosaccharides were the most abundant sugars, followed by polysaccharides, and starch was the least abundant in Leucadendron, Leucospermum and Protea stems. Differences in polysaccharide and starch content were minor, between AirEx and low O2 treatments, also between AirEx and high CO2 treatments. Lipid peroxidation was comparable between AirEx and high CO2 atmospheres. The AirEx, DCA and 2 % O2 treatments had an insignificant effect on total phenolic content of products. Further research is recommended under commercial conditions in AV+ type reefers, where automatic ventilation should be set to maintain a minimum of 2 % O2 and maximum of 15 % CO2 concentration during long-term sea freight shipping of Proteaceae cut flowers to ensure optimum product quality throughout the cold chain for an extended vase life.