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.