9/18/2016 Water binds the surface of solutes as they dissolve cha Water Activity Defined the solution nging the property of Water activity (a is a measure of free water or the Free water decreases as solutes are energy status of water in a system(food) dissolved ompete with the solutes Water activity is defined as ·Microbes n APictorl Den of Water Acmity for free molecules Vepor pressure of pure water sameC Movement of water vapor from food depends on femperature,humidity,and food composition Water in Food Water Activity as a Preservative All foods contain some water A low water activity inhibits microbial ·Free water growth Held inside the cell Salt.sugar.or drying lower the water -Maintains properties of free water activity of foods May be removed by pressure used as preservative of food to decrease ·Bound water the water activity and to preserve the food Part of the cellular molecular structure sugar and salt bind water Reduced motility drying removes water Does not maintain properties of free water 159/18/2016 15 • Water binds the surface of solutes as they dissolve changing the property of the solution • Free water decreases as solutes are dissolved • Microbes must compete with the solutes for free molecules 57 Water Activity Defined • Water activity (aw) is a measure of free water or the energy status of water in a system (food) • W d f d Water activity is defined as • Movement of water vapor from food depends on temperature, humidity, and food composition 58 Water in Food • All foods contain some water • F tree wa er - Held inside the cell - Maintains properties of free water - May be removed by pressure • Bound water - Part of the cellular molecular structure - Reduced motility - Does not maintain properties of free water 59 • A low water activity inhibits microbial growth Water Activity as a Preservative • Salt, sugar, or drying lower the water activity of foods - used as preservative of food to decrease the water activity and to preserve the f d oo - sugar and salt bind water - drying removes water 60