| It is difficult for common plastic films to meet the requirements of the gas transmission rate?TR?of packaging for high respiration rate or CO2 sensitive fruits and vegetables,and suitable micro-perforated films can enable fruits and vegetables to breath slowly,which significantly prolong the shelf life of fresh fruits and vegetables.Moreover,the cost of micro-perforated films are relatively low and the operation is rather simple.Therefore,the micro-perforated film served as modified atmosphere packaging has attracted more and more attention from researchers at home and abroad.Currently,the research on the preservation of micro-perforated film focuses on the traditional experiments that conduct multiply trials to seek for the most suitable micro-perforated films for packaged fruits and vegetables,however,the experimental cost is extremely high,worse still,the optimal micro-hole parameters of the micro-perforated film for fruits and vegetables may not be obtained.Based on this,the mechanism of gas TR and factors which influence on the gas TR of micro-perforated film are analyzed,as well as verified in the specific fresh-keeping of fruits and vegetables with micro-perforated films.The main research content and results are as follows:?1?The establishment and verification of mathematical model for the gas TR of micro-perforated films,together with the analysis and calculation of the end effect:based on the relationship between the micro-hole diameter D and the mean free path?of the gas molecules,ie,D?100?,the diffusion of gas through micro-holes follows the Fick diffusion law.The mathematical model for gas TR was established based on Fick diffusion law,and then it turned out that there was a marginal end effect of micro-holes,which hinders the gas TR of micro-holes,making the experimental value of O2 much lower than the theoretical prediction value,while the experimental value of CO2 a little higher.Subsequently,from experimental analysis,the end effect values of O2 and CO2 were found to be 0.4603 and0.4641,respectively.Finally,the modified value of gas changes are in accordance with the experimental value practically.?2?The effect of the distance between the micro-holes on the gas TR of the micro-perforated film.In the absence of physical conditions with temperature 23?and relative humility 50%,the daimeter of micro-hole was 40?m?120?m or 200?m,as well as the different distance between holes,namely 0.4mm?0.8mm?1.2mm?1.6mm and2.0mm,was studied,respectively.The results show that when the distance between micro-holes and micro-hole diameter exit L?6D,the effect of distribution distance on the TR of micro-perforated film is negligible;?3?The effect of different micro-hole parameters on the gas TR of micro-perforated film in the same area of micro-hole.The container was placed at 23?and relative humidity50%under no physical conditions.Different micro-hole parameters but the same area of micro-hole 10-2?cm2 were investigated.It turned out that the gas TR of 16 micro-holes with50?m in diameter were better than 4 micro-holes with 100?m in diameter,while 4micro-holes better than 1 micro-holes with 200?m in diameter.Similarly,when the pore area is 6.4×10-3?cm2,the same trend was also presented.In conclusion,the more the number of micro-holes,the better the gas TR of the micro-perforated film if they are in the same area.?4?The effect of the temperature on the gas TR of micro-perforated films in the same micro-hole parameters.The empty container covering the micro-perforated film was placed in a test chamber at 23°C and a relative humidity of 50%.The number of micro-holes was constant and the diameters were 80?m?120?m and 200?m,respectively,or the micro-hole diameter was unchanged?120?m or 160?m?while the number of micro-holes was 6?10and 14,respectively.The effects of temperature on the gas TR of micro-hole films were studied at 4??15?and 35?,and the result shows that it seems to temperature has little effect on the gas TR of micro-hole compared with film with no micro-holes.?5?The empirical formula of the gas TR of micro-perforated films was established.diameter and temperature.According to experimental datum,the empirical formula for the TR of micro-perforated films combined the number of micro-holes,the diameter of the micro-holes with the temperature was fitted,along with the micro-perforated film parameters were designed based on the respiration rate of the cherry tomatoes.The results show that the empirical formula obtained the same optimal micro-hole parameter as the theoretically established mathematical model.Therefore,the established empirical formula and the modified Fick law can well predict the gas TR of micro-perforated films.?6?The application of fresh-keeping cherry tomatoes under modified atmosphere with micro-perforated film.Based on the above research results,the storage and preservation of cherry tomatoes using two kind of micro-perforated films and a non-perforated control group were studied.The changes in the five indicators of weight loss,corruption rate,TSS content,TA content,and VC content in the three groups were observed within 8 days.The results showed that the micro-perforated film was more beneficial than the non-perforated film to the preservation of cherry tomatoes.In the above five check indicators,the preservation effect of the micro-perforated film was better than that of the control group.In particular,the micro-perforated film MP11 still maintained relatively favorable commercial value and nutritional value after 8 days,which it is the best packaging for preserving cherry tomatoes. |
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