Food Physics

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Food Physics
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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.

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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.

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Osmosis

• OsmosisFlow 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?
• TurgorWater pressure in cells to keep things
  like vegetables crisp..
• Salt from dressings will take water out.

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• Osmosis takes place in all canned fruits.
• Microbes have a water concentration of 80 where
  salt and sugar at 40-50.

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Water Activity

• Controlling water controls microbes.
• Water activity is indicated by aw.
• Common water activity formula is
• Aw Equilibrium relative humidity/ 100
• Equilibrium Relative Humidityreached when a
  foods rate of water loss in the environment
  equals its rate of water absorption in the
  environment.

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• 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 1023

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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

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• 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.

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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.

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pH Adjustment

• pH will change the water molecules around
  protein.
• Lets take a closer look at this concept.

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• 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.

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Lipid Physics

• What is the difference between vegetable oil and
  shortening?
• Hydrogenation

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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

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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.

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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.

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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.

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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.