WATER AND EMULSIONS:

WHY DO WE CARE:

• Substantial component of foods

• Primary solvent for life process

• Water is polar

  • Like dissolves like

  • Requires energy to change phases

    • Boiling point = 100 celsius (212 fahrenheit)

    • Melting point = 0 celsius (32 fahrenheit) 

• Why is water polar

  • Hydrogen is not electronegative

  • Oxygen is electronegative

PHASES OF WATER:

• Ice

  • When freezing water → molecules align to crystalline lattice → pushed molecules further apart

    • Lattice = held together with hydrogen bonds

  • Ice is less dense than liquid because the lattice expands when it freezes

    • Floats in water

    • How fish survive when lakes freeze over

      • Ice acts as an insulator → protecting water below from freezing solid

  • Formed from ice crystals

    • Must have a nucleus → center of crystals

      • Time 

      • Temperature

    • Rapid freezing

      • Large number of small crystals

      • Minimal dehydration → little physical damage to cells

      • Larger number of small crystals → better cellular preservation and quality

    • Slow freezing

      • Fewer ice crystals → grow in intercellular spaces

      • Water moves towards ice crystals → dehydrating cells

      • Larger crystals + cellular damage

    • Can be problematic in food

      • Recrystallization (melting then refreezing)

      • If air is dry enough + temp is cold enough → ice sublimates

        • Directly from solid gas

        • Dehydrates food

        • Freezer burn

      • Crystals = puncture cells → expel water

        • Thawed frozen meat = tough

        • Veggies = mushy upon thawing

    • Freezing point depression

      • Freezing point pure water: 0 degree celsius (32)

      • Adding solutes = depress freezing point

        • Salt in seawater = lowers freezing point = water more difficult to interact with itself 

      • EX: freezing ice cream in old fashion makers, salting icy roads

• Boiling point of water

  • Where vapor pressure of liquid equals pressure of surrounding = turns into vapor

    • 100 celsius (212) atm

      • Atm: atmosphere unit of pressure

        • 1 atm = pressure at sea level

  • Adding solute to water → boiling point can be increased

    • EX: salting water when boiling = boil at higher temperature = cooking food faster

  • Dependent on air pressure

    • High altitude = less pressure than sea level

    • Vapor pressure of water = less time to match surrounding air pressure at altitude

      • Water will boil faster at altitude → boil at lower temperature

        • Food will cook slower

IMPORTANCE OF WATER ACTIVITY:

• Free water = water that's not interacting with anything

  • Free to participate in reaction

  • Free to be used by microbes

• Bound water = interacting with various food components (salt, sugar, etc.)

• Water activity is about energy 

  • Ratio between vapor pressure of food when undisturbed balance with surrounding air media

    • Aw of pure water is 1.0

      • Lower Aw the less energy of water there is

  • Closely correlated with moisture content (not completely the same)

  • Measures accessibility of water for chemical reactions, enzymes, microbes

    • Directly related to shelf life

      • Lower water activity = longer shelf life

EMULSIONS VS. STABILIZERS:

• Emulsion

  • Homogeneous dispersion of two components that repel each other (butter, mayonnaise, dressing, milk, ice cream, etc.)

  • Made with use of an emulsifier

    • Homogenise polar + nonpolar compounds (water and oil)

    • Has both polar and nonpolar portions on same molecule to accomplish this (phospholipids)

    • Must create small enough droplets/fragments with physical force to be evenly dispersed

      • “Sheer” = whipping, mixing, blending, etc.

      • Can be done without an emulsifier but mixture will eventually separate

  • Oil in water (O/W)

    • Water is the continuous phase, with oil suspended in it

    • mayonnaise

  • Water in oil (W/O)

    • Oil is the continuous phase, with water suspended in it

    • Butter

  • Phospholipids

    • Phosphatidylcholine

      • Lecithin

      • Common sources: soybeans (soy lecithin), egg yolks

• Stabilizers

  • Can accomplish similar thing as emulsifiers

  • Carbohydrate chains (hydrophilic) that thicken water phase to prevent lipid droplets from reuniting + separating out

  • Xanthan gum

    • Commonly used in salad dressing

  • Carrageenan

    • Commonly used in ice creams