Studies On Technologies Of Hot Air Drying For Litchi Fruit And Packaging And Storage Of Dried Litchi Fruit

Litchi, as a featured fruit in south of China, has highly nutritional value. In this dissertation,'Wu Ye'litchi fruits coming from Zhangzhou, Fujian province as raw materials were dried . The blanching and color protection technology before the drying process, the drying technological parameters, the package and storage method after drying, and the safe storage moisture content of the dried litchi fruit were investigated. The HACCP system for drying process of litchi fruits was also established. The results of this dissertation provided important technological parameters and scientific basis for litchi fruits'industrial drying process.Effects of different blanching treatment conditions and color fixative concentrations on the PPO activity of litchi pericarp were studied. Through orthogonal experiments and ANOVA, the optimum pickling blanching and color protection conditions were obtained. The optimum pickling blanching conditions were: temperature 95℃, time 3 min, citric acid concentration 0.3%. And the optimum concentration ratios of color protection solution were: citric acid 0.2%, NaCl 2%, and ascorbic acid 0.3%.Drying rate changes of litchi fruit affected by different drying temperatures, different wind speeds and different loading conditions were investigated. The results showed that drying rate accelerated by the increasing of temperature and the wind speed, and the decreasing of load. Through orthogonal experiment, the optimum process conditions with drying efficiency as indicator were obtained: temperature 95℃, wind speed 3 m/s and load 5 kg/m2. The optimum process conditions with sensory value as indicator were obtained: temperature 70℃, wind speed 1 m/s and load 2.5 kg/m2. The changes of pericarp color and sugar content were studied during the hot air drying process litchi fruit. The results showed that the higher the drying temperature, the greater the loss of total sugar and reducing sugar, and the greater the color change, and sugar loss and color changes were mainly occured in the early stage of the drying process.Through color, total sugar and total acid content changes of dried litchi fruits at different water content, different packaging method and different storage conditions, and by the comparison of healthy fruit ratio after 6 months storage, the safe storage moisture content and the optimum packaging and storage conditions were obtained: dried litchi fruit water content 30%, vacuum-packing method and storage temperature 5℃.In order to improve product quality and ensure healthy and safety product, the HACCP quality management system was introduced into the litchi drying process. The results showed that the critical control points in litchi fruit drying process were: selection of raw materials (litchi fruits), drying temperature control, vacuum packaging and low temperature storage.