| As production grows and living standard of the masses is improved, the storage technology of fresh fruit has become more and more important because of the off-season consumption of grapes and other fruit substantially increased and the consumption style of fruit and vegetable is transforming quantity consumption into quality consumption. In response to this momentum, technical requirements for fresh-keeping of fruits and vegetables are much stricter. There are two technological puzzles during the storage period of grapes. One is that grapes are easily infected by bacteria and spoiled. The other is that the threshing, dry stems and other phenomena caused by dehydration-prone make grape lose its commercial value which will result in huge economic losses. Sulfur treatment is used most widely in various fresh-keeping technologies of grapes. However, this method has many problems. For example, if the dosage is too small, it will fail the fresh-keeping purpose while it will injure stored fruits if the dosage is too big, or even hurt humans and pollute environments.In order to solve problems above, this paper conducted a study from the following areas:1.A three-layer structure fresh-keeping packaging film which can control the release amount of SO2 fungicide was prepared by using dry composite method in this paper. The ingredients in three-layer structure of fresh keeping packaging films were determined and the compound craft of this composit film were also determined after several exploratory tests. The results are shown as follows:(1) The inner film was prepared by melting and mixing C resin and F resin with different proportions. Six types of inner films were prepared, with the weight percent of C which were 0,2%,5%,10%,16% and 25% respectively. The best prescription of the middle layer was:polyurethane adhesive (the main component) 10g, curing agent 0.5g, ethylacetate 10g, A 1.25g and B 1.25g. The outer layer was BOPP film.(2) Before the films were compounded together, the surfaces of the films were treated by self-made solution in order to improving the surface tension of the film. Then the bonding layer was coating on the outer film by the manual coating machine. Finally, the treated surface of the inner film was laminated with the surface sizing of the outer film, and the laminated film was rolling 2 or 3 times by film sealing machine. The laminated film was placed at room temperature for one or two days, then it was heat sealed into packaging bag.2. The influence of different blend ratio of F and C on the release concentration and release period of SO2 fungicide were studied by testing the polarity, water vapor transmission rate, oxygen transmission rate and crystallinity of inner film. The conclusions are shown as follows:(1)The SO2 concentrations released in packaging bags are different if the C content in inner film of packaging bags were different. The higher the C content in inner film, the greater the permeability of the inner film. More SO2 fungicide is produced if more water vapor and organic acids penetrate the inner layer to contact the fungicides A and B in middle layer.(2) SO2 fungicide (10～40ppm) can be released continuously from all kinds of prepared packaging bags for about 50 days. This concentration range is effective for retention of fruit quality.(3) The release rate of SO2 fungicide can also be adjusted to suit the rate required by different fruit varieties.3. Taking kyoho grapes.as experimental material, the fresh-keeping effect of packaging bags on grapes were studied by measuring the weight loss rate, shedding ratio, decay ratio, soluble solids content (SSC), PH value, hardness and good fruit rate of grapes every 10 days. The results are shown as follows:(1) The preservation effect is better in treatment groups as compared with that in the control groups. Grapes stored with fresh-keeping packaging bags can still maintain a relatively higher good fruit rate when stored for 60 days, the good fruit rates are all over 70%.However, the good fruit rates of CK1 and CK2 are 0 and 19.6% respectively. The water loss, berry drop and consumption of soluble solids and organic acids of grapes stored with fresh-keeping packaging bags were reduced. The firmness of grapes stored with fresh-keeping packaging bags was well maintained and the appearances of grapes stored with fresh-keeping packaging bags were improved. Especially when C content in the inner layer of fresh-keeping packaging bags is 5%-16%, the fresh-keeping effect were better. The good fruit rates are over 75%.(2) When grapes were stored for 50 days, SO2 residues in grapes of treatment group 3 and treatment group 5 were not detected, which were far lower than the standard of 10μg·g-1.(3) Fresh-keeping packaging bag prepared in this study can make litchi stay fresh for 21 days at low temperature.In short, the fresh-keeping packaging film prepared in this study not only makes the release amount of SO2 meet the requirements of preservation, but also does not hurt human body. The release amount of SO2 can be adjusted to suit the rate required by different fruit varieties (grape, litchi, longan and other fruits), which have a good fresh-keeping effect and a high practical value. The study of this fresh-keeping packaging film has taken leading places domestically. The choice of precursor of SO2 fungicide has the innovative attribute.
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