| Citrus ranks second among fruits produced in China. Postharvest fruit quality changes is a complex process affected by both genetic and non-genetic factors such as temperature, humidity, gas composition and other environmental factors. Postharvest rot is one of the chief reason leading to the loss of citrus fruit industry. As a safe and effective post- harvest handling techniques, heat treatment has been proved to be very efficient for many fruits and vegetables, but the heat treatment applied to Ponkan fruits and research on its long-term preservation is rarely reported. In this thesis, Ponkan fruits was used to study the effects of different heat treatments on storability, quality changes after harvest, and its mechanism was preliminary studied too. The main results are as follows:1. As an effective post-harvest processing technology, heat treatment can significantly improved the storage-tolerance of Ponkan fruits after harvest. Heat treatments, especially 55° C hot water immersion for 20 S significantly reduced the decay of citrus fruit during storage and shelf time. Heat treated fruits had smaller weight loss rate too. Results of small scale experiments showed that the heat treatment can suppress the occurrence of gray mold and penicillium disease. Given the significant effects of 55℃ hot water immersion for 20 s in improving the storage-tolerance of Ponkan fruits, this treatment had the potential to be popularize in large scale and applied to production practices.2. The effect of heat treatment on color, sugar and acid of Ponkan fruits during storage were studied. We found that Heat treatment had no significant effect on the color of Ponkan fruits after harvest. The content of sucrose decreased during storage, while the levels of glucose and fructose were increased, which may relate to the fact of degrading sucrose into glucose and fructose. Citric acid is the most important and abundant organic acid in Ponkan fruits, heat treatment can significantly decreased the contents of organic acid especially the content of citric acid. The sensory evaluation results show that heat treated fruits have a high score on moisture, freshness and finally sweetness and sourness. Thus, heat treatment can suppress the decline of flavor in Ponkan fruits during storage, making it more attractive to the consumers.3. Bioactivity is an important part of fruit quality. The contents of total phenolics and flavonoids decreased significantly in the first month, they have a trend to increase during the next long-term storage. Antioxidant activity of pulp in Ponkan fruits decreased after harvest, but the heat treatment can inhibit its decline, which make the fruits a higher nutritional value. Heated treated Ponkan fruits have a higher contents of flavonoids after a month’s storage, which may be related with the resistance in heated fruits.4.According to the characteristics of Ponkan fruits, the operating specification was made on harvesting, pretreatment, fruit choosing, heat treatment, working temperature controlling and sales. A citrus fruit postharvest heat treatment equipment was developed, including:transmission system, cleaning the cooling system, heat treatment systems, and strong wind drying system.5. Mitochondrial of Ponkan fruits was observed by SEM. Heat treatment can inhibit the degradation of mitochondrial and maintain the integrity of mitochondrial structure. Heat treatment have no significant effects on oxidative metabolism related enzymes (SOD, POD), and therefore heat treatment may functioned through other non-enzymatic systems. The contents of IAA showed no difference between heat treatment and the control, but the ABA content was significantly down regulated by heat treatment, which inhibited the aging process during storage. |
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