Litchi (Litchi chinensis Sonn.) is a commercially valued fruit mainly for its attractively red pericarp and exotic taste. However, the market value of the fruit is affected by pericarp browning, desiccation and postharvest decay. Current control measures include sulphur dioxide (SO2) fumigation, low temperature storage and high relative humidity (RH). Sulphur residues on fruit, moisture loss, altered taste and decay caused by Penicillium spp., limit the use of SO2 fumigation. Technology that can provide a potential alternative method to retain the quality of fruit is modified atmosphere packaging (MAP). In this study (Chapter 3), the effect of active and passive modified atmospheres on quality retention of litchi cultivars ‘Mauritius’ and ‘McLean’s Red’ was investigated. Results indicated that ‘McLean’s Red’ is more suitable for MAP technology than ‘Mauritius’. Lidding film–4 holes significantly reduced activity of oxidation enzymes, polyphenol oxidase (PPO) and peroxidase (POD), and retained higher pericarp colour. Lidding film–10 holes retained soluble solids concentration to titratable acidity ratio (SSC/TA) (~65), thereby preventing the loss of taste and litchi fruit flavour. In order to enhance the MAP technology further (Chapter 4), chitosan coating of fruit was also assessed. Chitosan (1.0 g L-1) combined with MAP effectively prevented decay, browning and pericarp colour loss in ‘McLean’s Red’. Chitosan (1.0 g L-1) integrated with MAP reduced PPO and POD activity, retained membrane integrity, anthocyanin content and pericarp colour. ‘McLean’s Red’ was found to be more suitable for the chitosan (1.0 g L-1) and MAP integrated treatment than ‘Mauritius’ in retaining overall quality. In addition, the effect of 1-methylcyclopropene (1-MCP) in combination with MAP was determined for both cultivars (Chapter 5). In this case 1-MCP (300 nL L-1) was most effective in preventing browning and retaining colour in both cultivars after 14 and 21 days of cold storage. The effect of 1-MCP (300 nL L-1) showed more potential on ‘McLean’s Red’ than ‘Mauritius’. At higher concentrations (500 and 1000 nL L-1), 1-MCP showed negative effects on membrane integrity, pericarp browning, PPO and POD activity in both cultivars. The effect of integrated postharvest treatments i.e. modified atmosphere packaging combined with chitosan and integrated MAP and 1-MCP as well as MAP and chitosan coating on foodborne bacterial pathogens (Escherichia coli O157:H7 and Staphylococcus aureus) spike-inoculated on litchi fruit surfaces, and Penicillium spp. decay were also investigated (Chapter 6). Results showed integrated MAP and chitosan (0.1 g L-1 and 1.0 g L-1) treatments significantly reduced high and low inoculums load of E. coli O157:H7 and S. aureus on litchi fruit after 21 days of cold storage. Integrated MAP and 1000 nL L-1 1-MCP resulted in higher disease severity. Integrated MAP and chitosan (0.1 g L-1 and 1.0 g L-1) treatments showed very good decay control. The total microbial population of the litchi fruit surface was also determined. Integrated MAP and 1.0 g L-1 significantly reduced the total microbial flora after 21 days of cold storage. / Dissertation (MSc)--University of Pretoria, 2010. / Microbiology and Plant Pathology / unrestricted

Penicillium species have been studied for over 200 years and the genus was first described by Link in 1809. Initially, morphological identification methods were used however, much diversity within the genus resulted in researchers seeking alternative techniques and approaches to improve accuracy. These methods involved biochemical analysis of secondary metabolites in conjunction with morphological examination. With the emergence of more accurate and rapid molecular identification tools, scientists embraced modem technology to address diversity challenges. In order to provide a more holistic approach towards the taxonomy of complex genera, morphological analysis remains an essential component in Penicillium identification. Penicillium species are omnipresent, dominant and problematic in postharvest environments. They are known to cause major losses in export markets due to fruit decay. The aim of this study was to identify species within the South African litchi export chain and develop a rapid method for Penicillium identification. This study used morphological as well as molecular identification methods in order to develop PCR-RFLP restriction maps for a number of dominant Penicillium species. Seventeen species of Penicillium were identified using conventional morphological methodology and DNA sequencing, both of which are laborious and time-consuming. Polymerase Chain Reaction-Restriction Fragment Length Polymorphism provided reliability and repeatability as well as being a cost-effective and rapid identification alternative. A combined phylogenetic study indicated that the taxonomic position of several species may need to be reconsidered. Fourteen species were differentiated from one another through digestion of the â-tubulin gene region with five restriction enzymes. Banding patterns correlated well with phylogenetic and biochemical data of related studies, indicating that this method holds promise as a rapid identification procedure for Penicillium species. / Dissertation (MSc)--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted