Assessing the suitability of polylactic acid flexible films for high pressure pasteurization and sterilization of packaged foodstuff

Effects of High Pressure (HP) pasteurization and sterilization processes on the properties of commercial biodegradable polylactic acid (PLA), used as packaging material, have been investigated. HP treatments have been performed at pressures of 200, 500 and 700MPa on PLA pouches, containing different types of food, ie. tap water, solid carrots, carrot juice and carrot puree. Process temperature was in the ranges 25-40°C and 90-110°C, respectively for HP pasteurization and HP sterilization. To the aim of assessing the suitability of PLA film for HP treatment of packaged food, the effects of treatments have been analyzed in terms of structural/morphological changes (i.e. crystallinity, density, orientation of PLA film) and of thermodynamics and functional properties (i.e. melting and glass transition temperature, permeability and solubility of gases and of water vapour). It has been found that HP pasteurization does not affect to a significant extent any structural and functional property of the treated material relevant for food packaging applications. Conversely, HP sterilization promotes the hydrolysis of the material accompanied by an increase of crystallinity of the film and a decrease of density of the amorphous phase related to the temperature/pressure history. These effects determine an unacceptable embrittlement and opacification of the material that makes it unsuitable for HP sterilization applications.