Transcript Food Physics - Warren County Public Schools

Food Physics
Water in Food
• Water has three states: Liquid, solid, &
gas.
• In food water is either added, removed, or
altered in food (typically altered)
• Ice floats due to hydrogen being spaced
further a part as compared to the usual
alignment.
• “Tetrahedron” is the 4 hydrogen bonds that
form between water molecules.
Interfacial Tension
• Water has different forces
– 1. Attraction to other water molecules.
– 2. attraction of water molecules for the
surface they may be on.
– 3. To each other when against air.
Osmosis
• Osmosis—Flow of water molecules from a
place of greater concentration to a place of
lesser concentration.
• Example-All vegetable wilting.
• Why are vegetables kept wet at stores?
Turgor—Water pressure in cells to keep
things like vegetables crisp..
Salt from dressings will take water out.
• Osmosis takes place in all canned fruits.
• Microbes have a water concentration of
80% where salt and sugar at 40-50%.
Water Activity
• Controlling water controls microbes.
• Water activity is indicated by aw.
• Common water activity formula is:
Aw = Equilibrium relative humidity/ 100
Equilibrium Relative Humidity—reached
when a food’s rate of water loss in the
environment equals its rate of water
absorption in the environment.
• Definition of mole :
1) The quantity of a substance whose
mass, in grams, is equal to its formula
weight. Ex: Iron (Fe) has a formula, or
molecular, weight of 55.85 grams. One
mole of iron would be 55.85 grams.
2) Avogadro's number: 6.022 x 10^23
Moles in Water
• Water has a concentration of 55.6 moles.
• If 1 mole is added to 1000 grams of water
it now contains 56.5.
• Water Activity is the number of water
molecules relative to the total number of
molecules present. What would the water
activity be in this example:
• 55.6/56.6 = .982 which would mean that
for every 1000 molecules of solution there
is 982 water molecules.
• In this case humidity inside the food would
be 98%.
Proteins
• Proteins function around water.
• Water & protein have a “synergistic”
relationship (mutual cooperation)
• Proteins always have a single layer of
water around them.
• The water layer is the reason why freezing
does not kill microbes.
• Even freeze dried foods have a water
layer.
pH Adjustment
• pH will change the water molecules
around protein.
• Let’s take a closer look at this concept.
• You have made curds and whey.
• The acid in vinegar stopped the amino
acids from bonding which caused the
curds. Basically the proteins collapsed out
of the milk.
• Precipitate is the fall out materials
technical name, something that comes out
of a solution that has evaporated.
Lipid Physics
• What is the difference between vegetable
oil and shortening?
• Hydrogenation
Role of Heat
• Oil is not passive in cooking.
• Melting Point-temp where fat becomes
liquid.
• Smoke Point-release of volatile molecules.
• Flash Point-ignitable vapor, volatile
molecules are heavier.
• Fire Point-oil will burn
Hydrophobic
• Oil and water
• Immiscibility-inability of two liquids to mix.
• Water is dipolar (energy) and fat that has
triacylglyceriades are not. Again with pH
this does change in proteins that have
lipids. Proteins will bond but the fat will
not.
Carb Physics
• Carbs absorb large amount of water in the
polymer stage.
• A polymer is a large molecule
(macromolecule) composed of repeating
structural units typically connected by
covalent chemical bonds.
• In this case the C, H, and O with oxygen
holding various groups together.
Starches
• Cold water little solubility, hot water it is
spaghetti time.
• Starch gels, forms a viscous (does not
flow well) liquid.
• Pudding is a common example due to the
polysacs.
Pectins
• A polysaccharide extracted from the cell walls of
plants, especially of fruits; under acidic
conditions it forms a gel. It is often used in
processed foods, especially jellies and jams
where it causes thickening (setting).
• Pectins are linear polymers of galacturonic acid
joined by bonds that allow side sugar chains.
Hydrogen during cooling bonds to lead to gels.
• Pectin has two gels: high methoxyl content and
low content methoxyl.
• Both used to make jelly, one high sugar the other
not.