Thesis: Degree of doctor of Philosophy in Crop Science 2019The preliminary experiment was done by using Jaffa orange variety to assess the effects of different concentrations of hexanal, calcium chloride and smoke treatment on physico- chemical quality. Jaffa orange fruits were separately (i) dipped in hexanal at 0.01%, 0.02% and 0.04% volume/voume for five minutes (ii) dipped in calcium chloride 1%, 2% and 4% weight/volume for five minutes (iii) fruits were smoked by burning 0.5 kg, 1.0 kg and 1.5 kg of dry banana leaves (iv) Untreated fruits (control). The fruits were evaluated under two storage conditions; ambient (28 ± 2 °C) and reduced temperature (18 ± 2 °C) and the data were collected at the 4th, 8th and 12th day after fruit harvest. Collected data were analysed by using R - software. Mean separation was done by using Tukey Honestly Significant Difference at p ≤ 0.05. Results of preliminary experiment showed that hexanal at 0.02% v/v and calcium chloride at 0.02% w/v and smoke treatment obtained by burning 1.0 kg of dry banana leaves were effective in maintaining physico-chemical quality of Jaffa orange. Then, hexanal 0.02% v/v, calcium chloride 2% w/v and smoke treatment obtained from burning 1.0 kg of dry banana leaves were selected and used in other objectives. The actual experiments were conducted for two consecutive seasons of 2016 and 2017 to assess the effects of hexanal, calcium chloride and smoke on physico- chemical, shelf life, nutritional quality and cost benefit analysis of two orange (Msasa and Jaffa) and two mango (Apple and Palmer) varieties. The study on post-harvest losses of these fruits along the supply chain was also conducted. Various physico-chemical parameters were assessed. Results showed that hexanal and calcium chloride significantly reduced physiological weight loss, maintained fruit firmness and increased total soluble solids of both mango and orange fruits relative to smoke treatment and the controls. Reduced temperature significantly lowered physiological weight loss over the ambient storage. Major sites of post-harvest losses were at harvest, transport, wholesale and retail stages of supply chain. Post-harvest treatments of fruits with hexanal and calcium chloride significantly increased the shelf life and reduced disease incidences relative to control and smoke treated fruits. Reduced temperature significantly increased shelf life of fruits over the ambient storage. Hexanal improved nutritional quality of the fruits followed by calcium chloride and the control. While vitamin C and total flavonoids were decreasing, total sugars and reducing sugar content increased with storage time. Further results showed that hexanal and cold storage conditions led to higher number of marketable fruits over other treatments. Smoke treatment had the lowest number of marketable fruits. Mango fruits treatment with hexanal and stored under ambient storage was the most viable post-harvest technique with positive net present value and cost benefit ratio greater than 1.0, thus, viable investments while the other post-harvest techniques had negative net present values and cost benefit ratio less than 1.0. Hexanal treatment is therefore recommended to farmers, transporters and traders for improved quality and shelf life of orange and mango fruits.