2009 Dehydration & Concentration

2009 Dehydration & Concentration - Unit Operations...

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Unit Operation: Reduction in water content Objectives: Protect from microbial growth by reducing water activity Reduce rate of deterioration of other quality parameters Unit Operations (3)
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grapes (raisens) Sun Drying of Foods tomatoes
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Requirements for water evaporation from a food Energy input (heat) Increases vapor pressure of food Compensate for cooling effect of evaporation Mass transfer Movement of water out of food into the surrounding atmosphere
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Non-linear relationship between water activity and water content Water activity (Aw) Water Content
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Effect of A w on deteriorative phenomena in foods
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Dehydrated foods: Less than 14% moisture Intermediate moisture foods: 20 - 50% moisture “semi-moist” Aw < 0.7 Moist foods: Some water removed, but Aw > 0.7 Require refrigeration
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Atmospheric pressure liquid ice vapor
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Processing factors affecting dehydration Surface area of the food surface / volume ratio Temperature differential between food and air hot air: greater water holding capacity
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2009 Dehydration &amp;amp; Concentration - Unit Operations...

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