THE INFLUENCE OF FLOW DIRECTION ON THE WATER-VAPOR PERMEABILITY MEASUREMENTS

The consequences of humidity exchanges between food and environment ar e always very important for the preservation of microbiological and se nsorial quality of the product. For a realistic shelf-life evaluation of sensitive food-products is therefore essential to know exactly the water vapour transmission rate (WVTR) through the packaging material. The measurement of this important diffusional property is commonly per formed without regard of the exchange direction and in conditions very far from those of reality: extremes temperature and humidity combinat ions as 38 degrees C and 90% of U.R. Thus, it was considered useful an d interesting to verify if the permeability phenomenon could be affect ed by the direction of flow and by the contact of dry or moist product . To such purpose measures of water vapor permeability were realized u sing PET and OPP pouches, filled with water or Calcium Chloride. The r esults achieved excluded the influence of the contact of dry or wet su bstance with the pouches walls and of the now direction on the determi nation of the WVTR for the materials and the conditions examined.