ABSTRACT
When the total pressure inside the package becomes lower than that of outside environment as a consequence of a more or less evacuation of the internal atmosphere, it is commonly referred to as vacuum packaging or hypobaric packaging. The degree of residual pressure inside the package can vary greatly, according to the time and intensity of the evacuation step during packaging operation. Vacuum packaging is usually the condition with a negligible amount of nitrogen, oxygen, and carbon dioxide, and can be with vacuumed headspace (in rigid or semi-rigid packages) or tight contact between packaging film and food surface (in flexible packaging). It is quite common to call 'hypobaric packaging' the condition where the residual pressure is equal or higher than 2.6 kPa but at subatmospheric pressure. Typically packaging of moist foods in fact cannot reach the residual pressure down below the water vapor pressure at the corresponding temperature. The effectiveness of vacuum packaging for shelf life extension is mainly due to the low or very low amount of residual oxygen, as a consequence of the air extraction: oxidative reaction and aerobic respiration are reduced. Moreover, vacuumed package may be seen to be
an effective means in eliminating possible biological and chemical contaminants from the space surrounding the food. The reduction of the package volume should also be noted as an important advantage of vacuum for flexile packaging.
