NDFS 250 Water~~
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Primary Functions of Water in Foods and Food Processing
- Solvent and dispersing or bulking agent
- reactant (hydrolysis reactions)
- rheology and texture
- microbial growth (spoilage)
- medium for heating and cooling foods
- cleansing agent
- mechanical processes (water knife!!! cool~~
explain dipolar H2O
unequal sharing of electrons... you know la
Hydrogen bonding of water
you knkow la
Water as a solvent, what's special about it?
dipolar nature of the water molecule allows it to engage in hydrogen bonding, ion-dipole, and dipole-dipole interactions with other polar or charged molecules
composition of solute and solvent
- unsaturated solution
- saturated solution
- supersaturated solution
the properties of a solution are affected by...
- the nature of the solvent
- the nature of the solute
- the concentration of solute molecules present
two key water properties affected by solutes...
- boiling point _.-^
- (instead of overcoming h-bonding, it's OH- in sugar... ion &dipole force now)
freezing point ^-._
for a molecule to escape the surface and become water vapor, the driving force of the heat eneryg must overcome what two forces?
- hydrogen bonding forces
- atomspheric pressure pushing down on the surface
effect of elevation on boiling pt
- for every 960 ft
- decreases 1 *c
what is colligative properties?
- properties of a solution that depend upon the number of molecules present, not upon their nature/size
- vapor pressure
- boiling point
- osmotic pressure
molecular weight unit?
- concentration (moles) or solute/ 1000gm of solvent
- concentration (moles) or solute/ 1000mL of solution
they're basically the same because 1gm water = 1mL water
NaCl got how many mole?
per mole of solute in 1000g of solvent
bp and fp?
- bp raises .052 C
- fp drops 1.86 C
phase changes in water
- melting (fusion)
- 80 cals from 0c ice to 0c water
- 540cals from 100c water to 100c steam
the amount of energy required to raise 1 gm of thing 1C*
when the thing is water = calarie/ gm
- change in temperature produced by heat; when all the heat added results in temperautre change in the substance, it is know as sensible heat.
- can be measured with a thermometer
- cannot be removed by normal drying
- no longer acts as solvent for solutes
- not available for biological growth/function
- has no appreciable vapor pressure
- only freezes at very low temperatures (<-5*c)
- needs high pressure to be removed from tissues
how to measure the water content of food?
- total water content (moisture)
- water activity (available water)
water activity (aw)
- a measure of free or available water
- vapor pressure of sample/vapor pressure of pure water
pure water's water activity ?
Lowest water activity values permitting growth of most bacteria?
Lowest water activity values permitting growth of yeasts?
Lowest water activity values permitting growth of most molds?
Lowest water activity values permitting growth of halophilic bacteria ?
Lowest water activity values permitting growth of exrophilic fungi
Lowest water activity values permitting growth of osmophilic yeasts
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