Thesis (MSc. (Horticulture)) -- University of Limpopo, 2019 / After harvesting litchi fruit, the red pericarp colour is rapidly lost resulting in discolouration and browning during storage and marketing. To mitigate this challenge, the South African litchi industry uses sulfur dioxide fumigation to retain litchi fruit red pericarp colour during extended storage and shelf-life. However, there are health concerns regarding the commercially used (SO2) fumigation for litchi pericarp colour retention due to high levels of SO2 residues in fruit aril. Therefore, this study aimed to explore the possibility of Uvasys slow release SO2 sheets to retain ‘Mauritius’ litchi fruit red pericarp colour when packaged in plastic-punnets and bags. Treatment factors were two packaging materials (plastic-punnets and bags), six SO2 treatments (control; SO2 fumigation and four SO2 sheets viz. Uva-Uno-29% Na2S2O5; Dual-Release-Blue35.85% Na2S2O5; Slow-Release-36.5% Na2S2O5 and Dual-Release-Green-37.55% Na2S2O5) and four shelf-life periods (day 0, 1, 3 and 5). ‘Mauritius’ fruit were assessed for pericarp Browning Index (BI), Hue angle (ho), Chroma (C*) and Lightness (L*). In this study, an interactive significant effect (P < 0.05) between packaging type and SO2 treatments was observed on ‘Mauritius’ fruit pericarp L*, C* and ho during shelf-life. Fruit stored in plastic-bags and treated with SO2 fumigation showed higher pericarp C* and L*, while SO2 fumigated fruit in plastic-punnets had higher pericarp ho. Lower pericarp BI was observed in SO2 fumigated fruit stored in plastic-bags, which showed less pericarp browning than fruit in other treatments. In general, commercial SO2 fumigation resulted in lower pericarp BI, and higher pericarp L*, C* and ho throughout the storage and shelf-life. Our correlation analyses results further showed that litchi fruit red pericarp colour was better preserved as SO2 treatment levels increased, especially in plastic-bags. In retaining ‘Mauritius’ litchi fruit red pericarp colour, Uvasys SO2 sheets were not effective when compared with commercial SO2 fumigation. However, commercially SO2 fumigated fruit were bleached throughout the storage and shelf-life. Furthermore, fruit from all treatments were spoiled due to decay and mould growth after day 5 of shelf-life. Inclusion of pathogen protectants is important in future research to demonstrate whether Uvasys SO2 sheet-packaging technology can retain ‘Mauritius’ litchi fruit pericarp colour. / Agricultural Research Council and National Research Foundation (NRF)

The use of sulphur as a method of postharvest disease control and colour retention in litchis is soon to be restricted by the European Union. It is therefore essential that new postharvest treatments and packaging techniques be developed in order to retain internal and external fruit qualities and thus allow for export. Good litchi quality is not only important for the export market but also for use on the local market. In this study, alternative methods for postharvest quality control were investigated with the aim of extending the litchi storage life to 40 days under modified storage. Packaging the fruit in polypropylene bags significantly decreased fruit water loss and resulted in an increase in shelf life, as determined by red colour and overall rind appearance. There was no distinct advantage of amodified atmosphere. The use of a punnet, lined with absorbent sheeting and placed within the sealed polypropylene bag, further improved the shelf life. The absorbent sheeting reduced the amount of free water and resulted in little pathogen infection, while the punnet was effective in protecting the fruit from damage. It was notable that most water loss occurred within the first 10 days of storage and that the majority would actually take place during the cooling phase. A hydrocooling technique was therefore investigated and was found to not significantly decrease water loss, possibly due to not hydrocooling the fruit for a long enough period of time. Temperature management was extremely important for both colour retention and pathogen control. It was found that treatments stored at 5.5QC showed better colour retention after the 40 days storage than the 1QC storage treatment. The higher storage temperature, however, enhances the potential for postharvest diseases. Three compounds, namely ISR 2000, 'Biosave' and F10, were tested for pathogen control. 'Biosave' showed the best results with the most effective concentration being 100 mill water and good pathogen control occurred when storage was at 10 C. Polyphenol oxidase (PPO) activity in the litchi rind was evaluated as it is thought to be closely related to browning of litchi fruit, probably due to the degradation of phenolics by PPO. Brown fruit had a high PPO activity whilst red fruit had much lower activity. It was also shown that PPO activity decrease over storage time, possibly due to product inhibition of the enzyme. The internal quality of the fruit was determined using the T88: acid ratio of the pulp, as it is well correlated to mean eating quality. For fruit to have excellent taste, it must have a T88: acid ratio of between 31:1 and 60:1. All the fruit had a ratio that met this criterion and would therefore ensure good eating quality. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.