The consequences of humidity exchanges between food and environment are always very important for the preservation of microbiological and sensorial 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 performed without regard of the exchange direction and in conditions very far from those of reality: extremes temperature and humidity combinations as 38 deg C and 90% of RU. Thus, it was considered useful and interesting to verify if the permeability phenomenon could be affected by the direction of flow and by the contact of dry or moist product. To such purpose, measures of water vapour permeability were realized using PET and OPP pouches, filled with water or calcium chloride. The results achieved excluded the influence of the contact of dry or wet substances with the pouches walls and of the flow direction on the determination of the WVTR for the materials and the conditions examined | Le conseguenze di uno scambio di umidita' tra alimento ed ambiente risultano sempre molto importanti per la conservazione della qualita' biologica ed organolettica del prodotto. Per una reale valutazione della conservabilita' dei prodotti alimentari sensibili all'umidita' e' quindi essenziale conoscere la velocita' di trasmissione al vapore acqueo (WVTR) attraverso il materiale di confezionamento. I metodi convenzionali di misura di questa importante proprieta' diffusionale sono solitamente riferiti a condizioni lontane da quelle reali sia per le combinazioni temperatura-umidita' relativa in cui si effettuano le determinazioni (38 gradi C e 90% di UR), sia per quanto riguarda le modalita' in cui il fenomeno di permeazione avviene. Non si tiene infatti in considerazione ne' la direzione di flusso del vapore d'acqua, ne' che nel caso reale il prodotto (umido o secco) si puo' trovare a diretto contatto con il materiale. Si e' cosi' ritenuto importante poter verificare se il fenomeno di permeabilita' fosse influenzato da queste condizioni e dalla direzione del flusso. A tal fine si sono effettuate misure di permeabilita' impiegando buste realizzate con PET ed OPP, riempite con acqua o cloruro di calcio. I risultati ottenuti hanno escluso l'influenza del contatto e della direzione di flusso sulla determinazione della WVTR per i materiali e le condizioni considerate

We examined the pasteurization effect of superheated steam containing micro-droplets of hot water (Aqua-gas, 115 deg C), superheated steam (120 deg C, 180 deg C) and hot water (100 deg C) to control Bacillus subtilis spores on the potato surface. Decimal reduction times of B, subtilis spores with the heating media were 2.8, 5.0, 6.3 and 6.8 minutes respectively. In case of the Aqua-gas, almost 90% of the spores were presumably washed away from the potato surface by condensed steam and the micro-droplets within 2.5 minute. After the condensation of the steam on the potato stopped, the potato surface was subsequently pasteurized effectively by the Aqua-gas since the surface was kept wet by the micro-droplets and it was heated with high temperature steam. To examine the pasteurization effect of actually cooking with these heating media, kakuni (boiled pork belly with soy sauce) and gyusuji (boiled beef tendon with soy sauce) were cooked using the Aqua-gas (115 deg C) , superheated steam (180 deg C) and a gas stove. The bacterial numbers of the food cooked with the superheated steam and the gas stove increased to more than 103CFU/g after 5 days of storage at 10 deg C. In contrast, the bacterial numbers of the samples cooked with the Aqua-gas were maintained at less than 300 CFU/g during storage.