Attachment
The packaging principle of MAP is to replace air in packaging bags and boxes with modified preservative gas (mixture of 2～4 gases according to food property), so as to change the internal environment of packed food, restrain bacilli growth as well as slow down the metabolic rate and extend the freshness or shelf life of the food. Take fruit and vegetable preservative as an example, fresh fruit and vegetable still respire after pick. They consume oxygen and produce carbon dioxide, which would result in increase of carbon dioxide content and decline of oxygen concentration. With high permeation film, oxygen could be supplied and carbon dioxide be vented through exchanging packaging gas with atmosphere. When the gas permeation rate equals to respiratory rate of fruit and vegetable, certain gas equilibrium concentration in the package is achieved. Then, fruit and vegetable could maintain weak respiratory rate without anaerobic respiration. Thereby, the maturation of fruit and vegetable is delayed and freshness is preserved. MAP could ensure food taste, nutritional ingredient and freshness period without applying preservative and additive.MAP material should be selected appropriately according to its gas permeation. The commonly used gas for MAP is a mixture of oxygen, carbon dioxide, nitrogen or mixture of oxygen and carbon dioxide. Therefore, gas permeation of oxygen and nitrogen should be tested accurately and respectively. Permeation of other gases should not be calculated simply by converting oxygen transmission rate (O2TR) according to experience. It can be imagined that index testing mistakes or inappropriate MAP material selection caused by incomplete gas permeation testing would not only cause great loss to enterprises but also waste the resource as well. At present, the commonly used methods for gas permeation test are different pressure method and equal pressure method. Equal pressure method instrument has limited testing objects. It can only test oxygen permeation (Labthink TOY-C2 Oxygen Permeation Tester) and carbon dioxide permeation. Nitrogen permeation testing instrument has not been developed by any enterprises. However, different pressure method instrument could test common gases such as oxygen, nitrogen, carbon dioxide and it has low cost and can provide self-control testing temperature (Labthink VAC-V1 Gas Permeation Tester). With the support of film theory, vacuum instrument of different pressure method can test common gas permeation as well as specimen diffusion coefficient and solubility coefficient. Compared with equal pressure method instrument, permeation testing instrument of different pressure method is more suitable for research institution and enterprises to have a comprehensive testing and analysis of MAP material.For more, contact Labthink Stella. SKYPE: stellali-labthink. +86-531-85068759.
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