Abstract
M.Sc.
Loss of quality occurs when tomatoes are stored for more than approximately 3-5 weeks at 12 °C. The most common disorders found in tomatoes during storage are colour development to an unacceptable shade of red, softening, shrivelling due to moisture loss, loss of flavour and fungal infections. Storage life of tomatoes is generally extended by storage under refrigeration. Further, extension of shelf life can be achieved by modified atmosphere packaging (MAP). This is done by sealing actively respiring produce in polymeric film packages to modify the 0, and CO, levels within the package atmosphere. Also, 1-methylcyclopropene (1-MCP) has been proven to be an effective postharvest treatment to prolong the storage life of tomatoes. In the present study four trails were conducted. In the first trial the effects of 1-MCP dosage rate and the colour stage of harvest on the quality of `Santa' tomatoes stored for 4 weeks at 12 °C were investigated. The results indicated that ripening related changes were delayed following 1-MCP treatment. 1-MCP treated fruit were firmer, had reduced TA losses, slower colour development, and reduced physiological disorders associated with long term storage. The stage of ripeness influenced the efficacy of 1-MCP on slowing down the tomato ripening process. 1-MCP was of little benefit for fruit treated at stage 4 of ripeness. In contrast, particularly when the 1-MCP dosage was high, 1-MCP markedly delayed ripening in fruit harvested at colour stage 2 and 3, but the quality attributes such as SSC were better in treated fruits harvested at stage 3. Relatively little difference was observed between 250 and 500 nL.L -I 1-MCP and thus 500 nL.Con fruit harvested at stage 3 of ripeness was used in the remaining experiments. Effects of MAP, 1-MCP and imazalil either as combined treatments or as single treatments were studied for their effect on the quality of tomatoes. Ripening related changes were delayed and loss of weight was significantly reduced following 1-MCP treatment and MA packaging in 17 gm thickness bags. Elevated CO, in MAP after a long storage period induced anaerobic metabolism with the generation of off-odurs and the proliferation of anaerobic microbes. Selected doses of imazalil (0, 0.5, 0.05, 0.005 and 0.0005 g.L.1 ) were evaluated for their effect on the fungal infections on tomato fruits. Imazalil at a rate of 0.005 g.L"' was found to reduce fungal infections by 50% when used in combination with MAP and 1-MCP. The combination of imazalil and MAP therefore appears to be the best treatment combination to facilitate export of 'Santa' tomatoes by sea. However, with regards to reducing the loss of TA, treatment with 1-MCP would be beneficial.