Study On Subfreezing Storage Technology Of Longan

The Longan(Dimocarpus longan Lour.),is a specialty fruit in the southern China.It is one of the main fruit in the Fujian.The planting area and output of Longan in China is premier in the world.Longan fruits have an abundance of nutrition,high edible value and medicinal value.It has been regarded as treasures among the fruits since ancient times.Nutrition analysis showed that:there were rich glucose,sucrose, protein,fat,vitamins and a variety of adenine,choline in longan meat.The physiology metabolism of Longan is strong after post-harvest due to the fruits were ripened in high temperature and humidity summer(August～September).Thus,the storage and sale of longan has a serious of problems,such as water loss easily at normal temperature,browning and decay.In this thesis,freezing fresh was used in the Longan storage.The Longan's freezing and the optimum storage temperature were discussed.Base on above,we also investigated the effects of Browning inhibitor treatment,ozone treatment,and modified atmosphere packaging on fresh longan freezing.The results were as follows:1.The Wulongling,Fuk eyes,the Quanzhou,pumingan,Dongbi,Shek Kip were selected to discuss.The results showed that the freezing point of varieties of fruit longan is between -2.6℃and -3.2℃,the freezing point of longan fruit related closely to soluble solids content and the rate of the aquifer.Three stages of Longan fruit freeze was not obvious,the largest ice formation zone -2℃～-14℃.2.Take Wulongling species as experimental sample,its freezing point is -2.7℃. Taking good fruit rate,browning index,respiratory rate,titratable acid(TA)and PPO activity peel as indexes,we discussed the effects of different storage temperature -3℃,-4℃and -5℃on the storage quality of Longan.The results showed that freezing significantly inhibited the respiration and enzyme activity,slowed nutrient loss.The longan fruit stored in -3℃,has only slightly frozen,and its ice rate was only 7%.It is in this temperature that the quality of longan can be better maintained.3.The main problems during subfreezing fresh longan were pericarp browning,small changes in pulp quality.Therefore,the test investigated the effects of five kinds of browning inhibitors,and determined of the optimum composite browning inhibitors and the best immersion time by L₁₆(4⁵)orthogonal experiments.4.Compared with the non-treating fruits,we respectively adopt ozone 5 min,10min and 15 min to pre-treat the longan,and studied the effects of different ozone treatment time on the storage quality of longan.Results indicated that the effect of ozone treatment 10min was more obvious.5.Combining ozone treatment with modified atmosphere packaging,we investigated the effects on fresh Logan.We investigated the effects of concentration of oxygen, carbon dioxide concentration and loading of the pack on the storage quality of longan. by L₉(3⁴)orthogonal experiment.The results showed that:the treatment(ozone 10 min,1%O₂,6%CO₂ pack loading 450 g)could retard the occurrence of longan pericarp browning,maintain a relatively high rate of good fruit and fruit TSS level, inhibit the peel PPO activity,and maintain the integrity of skin cells,reduce formation of lipid peroxidation product MDA to extend the storage period.