| Fresh fruit corn(sweet corn)and fresh waxy corn are popular for rich nutritional value and unique flavor.However,the harvest period of fresh corn is very short and it is difficult to preserve them for a long time.So there are two ways to store corn:storing in low temperature and quick-frozen corn.When eaten,the quick-frozen corn is used to be heated by hot water.The speed of hot water heating is slow.The nutrition and flavor of the corn gets lost a lot and the taste of the corn become very poor.The speed of microwave heating is high.It is convenient and quick heating by microwave.This heating method can maintain the nutritional components and flavor of the corn.The corn will lose a large amount of water when it is heated in the microwave oven exposed.This will cause the corn becoming too dry and too hard to eat.If the corn is heated in a microwave oven with an ordinary packing bag,the huge pressure of water vapor can break through the packaging bag.As a result,the product can not be sold.In this research,the laser etching film is used to make the packaging bag,which can keep the corn maintain its moisture during the microwave heating process and ensure the packaging is intact.The water activity,moisture content and weight loss of quick-frozen corn were measured during the microwave heating process.The temperature of corn was tested after different microwave heating times and the accurate heating times were determined when the temperature was most suitable for people to eat.The volume of the packaging bag,the length and diameter of corn were measured.The effective volume of the water vapor in the packing bag was calculated.The thermal performance of BOPA/LDPE and BOPA/RCPP packaging materials was tested.The effect of microwave heating on BOPA/RCPP BOPA/LDPE was observed.Heat sealing strength and impact resistance of packaging bag were tested.The reason of breaking was analyzed.The length of quick-frozen corn was 10cm.The optimum microwave heating power was 800W and the time was 4min.The melting temperature of RCPP and LDPE is 144.05? and 109.88? respectively.So the heat resistance of RCPP is higher than that of LDPE.The pressure in the package was calculated according to the equation of ideal gas.The pressure of bags packaging fruit corn is 5.36MPa.The pressure of bags packaging waxy corn is 6.10MPa.The heat sealing strength of BOPA/LDPE and BOPA/RCPP packaging bag is 30.71MPa and is 36.37MPa respectively.The impact strength of BOPA/LDPE film is 72.28MPa and the impact strength of BOPA/RCPP film is 89.57MPa.The relationship between the pressure in packaging bag and the amount of water diffusing through the micro pore of the laser etched film was discussed from the theoretical point of view.The relationship between the pressure in packaging bag and the sealing strength and the impact strength of the package bag was also discussed.The pressure in packaging bag is calculated by the amount of water diffusing through micro pore subtracting from the amount of water vapor spreading from the corn during microwave heating.When the impact strength of the packaging bag is exactly equal to pressure generated by the remaining water vapor in the packaging bag,it comes to the critical state.At this time,the micro pore area of the packaging bag is the smallest and the water distribution is the least.Besides,at this time,the phenomenon that the packaging bag is broken does not appear. |
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