Study On The Effects Of Modified Atmosphere Packaging And Ozone Treatment On The Quality Of Litchi

Litchi (Litchi chinensis Sonn.) is one of the most competitive fruits both in domestic and international markets. Now the medical treatments such as chemical medicine (disinfectant, antiseptic) with low temperature, sulfur dioxide treatment before dipping HCl were widely used, but chemical pollutions and safety problems were brought. In this text, the effects of different oxygen and carbon dioxide concentrations, Modified Atmosphere Packaging (MAP) treatment, ozone treatment and combination treatment on physiology, quality and decay of litchi during the storage period were studied. The details are specified as follows:1．Using good fruit rate, PPO activity and titratable acid (TA) of litch as reference indexes, effects of different temperatures on litchi quality were studied. It was found that 1℃not only inhibited respiration rate and polyphenol oxidase (PPO) activity of litchi, but also caused pericarp browning and nutritive loss which results from chilling injury. When the temperature was 5℃, respiration rate and PPO activity increased, good fruit rate and TA content decreased. The single-factor experiment indicated that 3℃was the optimal storage temperature for litchi.2．Comparing with the control group, effects of ozone treatment with 5min, 10min, and 15min on extending litchi storage lifetime were studied. The results showed that ozone treatment significantly prevented pericarp browning, maintained total soluble solids (TSS), V and titratable acidity (TA) contents, delayed anthocyanin decomposition, decreased PPO activity and cell membrane permeability, promoted superoxide dismutase (SOD) activity. However, it had no effect on peroxidase (POD), malon-dialdehyde (MDA). Furthermore, it accelerated the decline of flavonoid and phenolic content. Ozone treatment with 10 min was more effective.3．The effects of different oxygen and carbon dioxide concentrations on the quality of litchi, which were stored at 3℃for 10 days were studied by single-factor experiments. The results showed that the suitable low oxygen and high carbon dioxide treatment slowed down occurrence of pericarp browning, decreased respiration rate, maintained TSS, TA and Vc contents, promoted the activities of POD and SOD, inhibited cell membrane permeability and MDA content. Low oxygen inhibited PPO activity, but high carbon dioxide had no effect on it. However, low oxygen treatment accelerated the degradation of anthocyanin, flavonoid and phenolic content. The optimum range of O₂ and CO₂ is 3%～9% and 2%～8% respectively.4．The effects of oxygen concentration, carbon dioxide concentration and the carrying capacity on litchi quality were studied by the L₉(3⁴) orthogonal experiment. The range analysis indicated that according to the effect of three factors on litchi quality, CO₂>O₂>carrying capacity. In this experiment, best results were obtained in following conditions: 6%O₂, 5%CO₂ and 475g carrying capacity.5．To study physiological and biochemical changes of litchi, the MAP treatment and combining MAP with ozone treatment methods were used. MAP treatment (6%O₂+5%CO₂) prevented pericarp browning, maintained TSS, TA and Vc contents, inhibited PPO activity, cell membrane permeability and MDA, stimulated POD, SOD activity, but accelerated the degradation of anthocyanin, flavonoid and phenolic content. Comparing with MAP treatment, combination treatment (zone10min+6%O₂+5%CO₂) was less effective on inhibiting cell membrane permeability, PPO, SOD, POD activities. It had no effect on nutritive material, anthocyanin and flavonoid contents.