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dorothyayaya
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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
- transport
- mechanical processes (water knife!!! cool~~
- )
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explain dipolar H2O
unequal sharing of electrons... you know la
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Electrostatic interaction?
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Hydrogen bonding of water
you knkow la
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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
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solution
composition of solute and solvent
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aqueous solutions
- unsaturated solution
- saturated solution
- supersaturated solution
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the properties of a solution are affected by...
- the nature of the solvent
- the nature of the solute
- the concentration of solute molecules present
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two key water properties affected by solutes...
why?
- boiling point _.-^
- (instead of overcoming h-bonding, it's OH- in sugar... ion &dipole force now)
freezing point ^-._
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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
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effect of elevation on boiling pt
why?
- for every 960 ft
- decreases 1 *c
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what is colligative properties?
eg.
- properties of a solution that depend upon the number of molecules present, not upon their nature/size
- vapor pressure
- boiling point
- freezingpoint
- osmotic pressure
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molecular weight unit?
g/mol
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molal solution?
molar solution?
for water?
- concentration (moles) or solute/ 1000gm of solvent
- concentration (moles) or solute/ 1000mL of solution
they're basically the same because 1gm water = 1mL water
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NaCl got how many mole?
*2!
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per mole of solute in 1000g of solvent
bp and fp?
- bp raises .052 C
- fp drops 1.86 C
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phase changes in water
- evaporation
- freezing
- melting (fusion)
- sublimation
- vaporization
- condensation
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latent heat
- 80 cals from 0c ice to 0c water
- 540cals from 100c water to 100c steam
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specific heat?
the amount of energy required to raise 1 gm of thing 1C*
when the thing is water = calarie/ gm
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Sensible Heat?
- 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
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Bound water?
- 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
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how to measure the water content of food?
- total water content (moisture)
- water activity (available water)
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water activity (aw)
- a measure of free or available water
- vapor pressure of sample/vapor pressure of pure water
btw 0-1
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pure water's water activity ?
1
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Lowest water activity values permitting growth of most bacteria?
.91
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Lowest water activity values permitting growth of yeasts?
.88
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Lowest water activity values permitting growth of most molds?
.80
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Lowest water activity values permitting growth of halophilic bacteria ?
0.75
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Lowest water activity values permitting growth of exrophilic fungi
0.65
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Lowest water activity values permitting growth of osmophilic yeasts
.60
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