{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

water 3-10

S water activity aw s aw vapor pressure of water in

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ure of water in sample Vapor pressure of pure water Aw = 0.95 1.0 All Microorganisms (MO) can live Aw = 0.91-0.95 Important bacteria cannot survive. Aw = 0.87-0.91 Dangerous bacteria and yeast can survive Aw= 0.80-0.87 molds can survive s s s s Water Activity Food Beef Watermelon Lettuce Pound Cake White Bread Cheddar cheese Corn syrup Aw 0.95-0.99 0.95-0.99 0.95-0.99 0.90-0.95 0.90-0.95 0.80-0.90 0.60-0.70 % water 50 93 96 18 38 41 26 Functions of Water in Food Preparation. s Medium for Transfer of Heat. s Absorbs heat and sets up convection currents. s Equalizes temperature throughout food. s Good conductor of heat. Readily gives up heat to food. Transfer of Heat Conduction: Transfer of energy from one molecule to the adjacent molecule in a continuous and progressive fashion. Heat goes from the source to the pan to the food. s Convection: Transfer of heat by the circulation of currents of hot air or liquid. s Functions of Water in Food Preparation s Dispersing Medium s Dispersed particles could be crystals, cells, liquid droplets, gas bubbles. s Continuous phase: usually water but it could be oil. Types of Dispersions 1. 2. 3. Solutions Colloidal Dispersion Coarse Suspensions 1. Solutions Solutions: Smallest particle size of the three types of dispersion s Example sugar solution (< 1 mmicron) s Starch and protein too big to form solutions. s Most stable of the three types of dispersions. s 2. Colloidal Dispersions 2. Colloidal Dispersions. Particles are larger than in a solution but smaller than in coarse dispersions. s Colloidal systems, two phases = Dispersed phase & continuous phase. s Continuous phase extends throughout system s Dispersed phase: Isolated or disconnected. s 2. Colloidal Systems s May be a combination of solid, liquid or gas. s A. Emulsion: liquid in liquid s B. Sol: Solid in a liquid. s C. Gel: Liquid in solid s D. Foam: Gas in liquid A. Emulsions Types of Emulsions s Oil in water emulsion: Oil dispersed phase Water continuous phase Example: Mayonnaise s Water in oil emulsion Water dispersed phase Oil continuous phase Example: Butter s B. Sol Dispersed phase solid s Continuous phase: liquid s Example: gravy s Sols are pourable because the continuous phase is liquid. s Temperature and concentration of solid determine these properties. s C. Gels Dispersed phase: Liquid s Continuous phase: Solid s Example: gelatin, custard s Syneresis: Weeping or draining of liquid from a gel s Cranberry jelly is a good example s D. Foams Dispersed phase: Air s Continuous phase: Liquid s Examples: egg foams, milk foams s They contribute to volume and texture of various food products. s 3. Coarse Suspensions s Coarse Suspensions: Mixtures of substances, larger than in colloidal suspension. s Influenced by gravity s Tend to separate s EX. oatmeal flakes in water, uncooked starch mixture....
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online