WATER. WATER'S IMPORTANCE. Solvent Most molecules dissolved in water Reactant Water's involvement in hydrolysis reactions Product Water's involvement in condensation reactions Heat transfer medium E.g. boiling, steaming, cooling. WATER'S IMPORTANCE. Texture Juiciness, mouthfeel
UNDERSTANDING THE PHYSICAL AND CHEMICAL PROPERTIES OF WATER IS IMPORTANT IN THE STUDY OF FOOD AND PROCESSING
Water capable of bonding to 4 other water molecules
Unique properties of water from other hydrides
H-bond NOT a static phenomenon
T dependentSTRUCTURE OF WATER
Association of water to hydrophilic substances
1 atm (sea level)
So does it take longer or shorter to boil an egg in the Rocky Mountains? Why?
Let's go back to our egg, what would happen if you added salt?
Recommended that you add salt to water at high altitudes
Freezing point lowering
What explains all this?
P = P*/X1
P = vapor pressure of solution; P* = vapor pressure pure solvent; X1 = mole fraction of solute; x = grams solutes in solution; 55.5M = moles of water per liter
Osmotic pressure of solutions
Ionization of water
Keq = [H3O]+ [OH]-
[H3O]+ [OH]- = Keq = Kw (Water dissociation constant)
[10-7] [10-7] = [10-14]
HOAC H+ + OAC-
pKa = -log Ka
Keq = [H]+ [OAC]-
pH = pKa + log [salt]
What do we
call this point?
What is this point and its significance to food systems?
Overall eq: H+ + HCO3-H2O + CO2
Highly perishable foods aw > 0.9
Intermediate moist foods aw = 0.6-0.9
Shelf stable foods aw < 0.6
aw = p/pO=%RH/100
Crackers that experience a
temperature rise during
At the same moisture content which
would spoil faster?
Vit C loss
aw is a major HURDLE for microorganisms but
not the only one
A) Microbial stability
B) Chemical stability
- unstable w/o water, no H-bonding
C) Enzyme stability