Water

Vapor Pressure

-Affects release of volatile compounds from food to create aroma and flavor -Release of compounds from food as water evaporates ➡️ aroma and flavor

Altitude, AP, & BP

-As altitude increases, AP and BP decrease

Dehydrating and drying fruits and vegetables requires input or removal of energy?

-Dehydrating and drying fruits and vegetables requires input of energy to convert liquid water into water vapor. -Since fruits and vegetables may consist of at least 90 percent water, the cost of processing is significant.

How does water's molecular structure make it a good solvent?

-Dipole nature -Net positive charge on protons

Surface Tension

-Due to intermolecular forces (H bonds) pulling H2O equally -At surface, H2O is pulled inward -The surface "resists" compression -Affected by what is in the water (solute, dispersant, emulsion)

Freezing

-Max density at 4°C, then decreases as it freezes -Ice expands upon solidifying due to molecular repulsion between electrons -Frozen water has a highly organized rigid geometric pattern

Latent Heat & food processing

-Preparation of frozen food, at least 80 calories must be removed for every gram of water which is changed from liquid to ice. -Ice cream and frozen desserts also require significant energy removal to form ice crystals.

How do surfactants change the surface tension?

-Reduces surface tension of water -Breaks H bonds to release dispersants (e.g., dirt) -Hydrophobic portion takes up oil -Forms a micelle

Use of Solutes to modify BP

-Salt and sugar reduce VP of a solution, so more heat energy is needed to bring solution to a boil

Applications of Solute and FP/BP

-Takes more time to freeze desserts containing sugar compared with foods with less sugar -Frozen desserts with a lot of sugar melt more quickly compared with those with less sugar

1 g mole salt (58 g) in 1 liter of water reduces FP by

3.72º C (ionizes, 2X the effect of sucrose per mole)

Many foods are > ____% water

90

Water & cooking

Good cooking medium - hard to burn foods by boiling & steaming compared to broiling, barbecuing, or frying

Vapor Pressure definition

Pressure that gas exerts on the liquid and the energy required for the liquid to vaporize

Specific Heat

The amount of energy required to increase the temperature of a substance by one ° C

Effects of sucrose & salt on freezing point of water

-FP of water is reduced because of lowering of VP (vapor pressure) caused by solutes

Water & Energy

-High Melting Point and Boiling Point -Used to cool food -Large temperature range in a liquid form

Unusual properties of water

-High heat of fusion -High heat capacity -High heat of vaporization -High BP, FP -High surface tension -Ice (at Zero °C) has lower density than liquid water (at Zero ° C)

Phase Changes

-Impacts the energy in the hydrogen bonds -Phase (solid, liquid, gas) of water affects the properties of the food

Pressure cooker & BP

-increase BP ➡️ faster cooking -Pressure cooking is used in canning of low acid foods (>pH 4.5, vegetables, meats) to kill microorganisms (Clostridium botulinum spores -resistant to heat)

pH standard

-water is pH 7 -Logarithmic scale

Freezing point

0 °Celsius, or 32 °F.

Chemical and Functional Properties of Water

1. (Almost) Universal solvent (e.g., salts, proteins, sugars) 2. Dilutant / Dispersion Medium 3. Medium for ionization of acids and bases and other chemical reactions 4. Transfers chemicals more easily for tasting -Role of saliva 5. Odorants are often fat soluble 6. Energy 7. Formation and stabilization of systems (solutions, dispersions, suspensions, foams, gels) 8. Moisture and Water Activity 9. Plasticizer

Why is water's density unique?

1. -Ice (at Zero °C) has lower density than liquid water (at Zero ° C) -More volume (less density) in a solid form

Role in water in food

1. Affects texture, appearance and taste - interacts w/ proteins, CHO and lipids 2. Great medium for chemical & biochemical rxns, microorganisms grow better in moist foods 3. Water content is related to perishability of foods

Water bonds

1. Covalent bond of H & O within the molecule Equal sharing of electrons Difficult to break 2. Hydrogen bond between water molecules Unequal sharing of electrons Much less energy (than covalent) to break so allows water to easily react with other compounds

Surface tension is affected by:

1. Emulsions 2. Surfactants

Interactions between water and food molecules

1. Hydrogen bonding 2. Ionic interaction 3. Hydrophobic interactions

Water: Standard in Chemistry and Physics

1. Specific Heat 2. pH 3. Specific Gravity 4. Vapor Pressure affected by solvents 5. Density (mass/volume) = 1 g/ml 6. Surface tension

1 g mole sucrose (342 g) in 1 liter of water reduces FP by...

1.86 C

1 gram molecular weight ionizing solute per liter =

1.86 °C decrease in freezing point *per particle*

Latent Heat

A change in the state of matter requires energy (which is usually measured in calories) but no temperature change. Each gram of pure water requires 1 calorie to raise its temperature by 1 degree C.

BP & elevation

AP decreases with increasing altitude, VP of water required to overcome these decreases correspondingly so BP decreases.

The number of particles dissolved in a solution (solute concentration) affects the BP and FP

Every gram of solute particles added to water lowers the freezing point by a precise amount.

What 3 forms are water found in food?

Free Bound Entrapped

Boiling point

at sea level is 100° Celsius (C), which is equal to 212 °Fahrenheit (F)

Energy removal

change in state from gas ➡️ liquid ➡️ solid Also used in cooking and preservation

Energy input

change in state from solid ➡️ liquid ➡️ gas Food cooking and preservation

In high elevations, is BP higher or lower?

lower

Sugar is what type of compound?

non-ionizing

A g mole of salt ....

readily ionizes) has twice the effect on BP as that of sugar- little practical use due to unpalatability and health effects

BP of water

temp at which VP (vapor pressure) of water just exceeds atmospheric pressure (AP)

Volatility

tendency of a substance to vaporize; related to VP of the substance

Commercial food processing & BP, AP

use of partial vacuum to simulate low AP ➡️ lower BP ➡️ used in evaporation of fruit juices to produce concentrate w/ preservation of color, flavor, vitamins

Boiling and freezing point are governed by what?

vapor pressure

Association of water molecules

➡️ Ability to form multiple hydrogen bonds in three dimension -Highly electronegative oxygen partially draws electrons from two covalently bonded hydrogen atoms -A single water molecule is able to hydrogen bond with 4 others -Thus, water behaves as a cluster of strongly H-bonded molecules