ATMOSPHERIC AND VACUUM FREEZE DRYING KINETICS OF SHRIMPS

摘要

Freeze-drying is a mild dehydration process, usually carried out under vacuum andrnbatchwise; its fixed and operating costs are very high, due to the combined designrnand energy requirements of freezing and vacuum keeping. As a consequence, foodrnindustry does not utilise freeze drying as widely as it should, if reference is madernto the excellent quality of freeze dried products with respect to thermally driedrnones. To extend the utilisation of freeze-drying, a different technique is proposed.rnA fluidised bed of absorbent, operating at atmospheric pressure, captures waterrnvapour formed during sublimation.rnFirst experiments are carried out with shrimps and atmospheric freeze dryingrnkinetics are compared with those measured in vacuum freeze-drying.rnResults obtained so far show that freeze-drying time at atmospheric pressure isrnhigher than that detected in the conventional process under vacuum. To overcomernthis problem, two pretreatments are proposed I.e. vacuum thermal drying andrnosmotic dehydration. The effect of these pretreatments on freeze-drying kineticsrnunder vacuum and at atmospheric pressure is analysed and discussed.