Food Chem Mid 1

Water

Affects Texture

Enables Reactions

Supports Growth of Microorganisms

Equal donor and accpetor sites → large attractive forces

Hydrogen Bonds

H atom bound to a highly elecronegative atom (N, O, F,) experience attraction to another nearby electronegative atom.

Water binding / Hydration

Describes the tendancy for water to assosiate with hydrophilic substances.

Ability of proteins to hold wtr within food system

Water Holding Capacity

Ability of macromolecules to physically entrap large amounts fo water.

Physically entrapped water

No flow from food (even if cut)

Behaves during processing close to pure water

Ions as a water solute

Hinder water mobility more than any other solute

Ionic bonds much stronger than H-bonds which disrupts waters structure

Hydration Shell is formed

Neutral Groups Capable of H-Bonding

Interactions weaker than water-ion interactions

Interactions btw wtr and solutes takes places

Occurs with various groups

Nonpolar substances

Hydrophobic hydration occurs (water molecules become ordered around apolar solutes)

System adjusts to minimize interaction btw water and the apolar solute

Physical seperation.

Water as a solvent

Formation of H-bonds btw water and polar solutes

Solubility declines in molecules with greater than 5 carbons

Water activity

Ratio of vapor pressure of the water in the food product to that of pure water at the same temperature.

Reflects intensity with which wtr associates with nonaqueous consitiuents.

Raoult’s Law

Adding a solute lowers vapor pressure of the solvent because the additional solute particles interact with solvent. Less solvent movlecules will be able to enter the gas phase, resulting in lower vapor pressure

Free water

Water that can be squezed out of a food

Avalible for chemical rxns

Bound Water

Water that is physically or chemically attached to compounds such as salt, sugar, gums, etc.

Moisture content

Total amount of water in a sample on a wet or dry basis.

Does not say type of water

ERH of food

RH of air surrounding the food at which product neither gains nor loses its natural moisture & is in equilibrium with the environment

Moisture sorption Isotherm

Relationship btw Aw, MC, at a specific temperature

Unique for each product

Zone 1 MSI

Most strongly “sorbed” (?) water and least mobile.

Remains unfrozen at -40C

Doesnt act as a solvent, behaves as part of the solid

Amt of water < potential sorption sites represented by all the polar or other active groups of the solute molecules.

Zone 2 MSI

Poplates 1st layer sorption sites still avalible

Assosiates with neighboring wtr molecules in 1st layer (primarily H-bonding)

Zone 3 MSI

High moisture part of curve (95% of wtr)

Very Mobile

Avalible as a solvent and supports the growth of microorganizms and enzymatic rxns.

Desorption

Type of MSI

As wtr is removed from food the Aw and MC is measured

Adsorption / Pre-sorption

As wtr is added back to dried food Aw and MC is measured

Hysterisis

Difference in ERH results between Absorption and Desorption

Would be due to structural collapse

Ways to minimize Aw

Aw Depressors

Humectants

Dispersed Systems

Most foods, heterogeneous mixture of componetnts

properties not given by their chemical composition

Dispersions

A system of discrete particles in a continuous phase

Foam

Dispersion Type

Phase: Gas

Continuous Phase: Liquid

Emulsion

Dispersion Type

Dispersed Phase: Liquid

Continuous Phase: Liquid

Sol, Suspention

Dispersion Type

Dispersed Phase: Solid

Continuous Phase: Liquid

Coarse Dispersion

“Suspentions”

Particle size > 1 um

Colloidal Dispersion

Particle size 1nm - 1um

Solution (Sol)

Dissolved phase

Particle size < 1nm

Suspention

Large particle size

Sedimentation possible in a short amount of time

Food Interfaces

boundries between phases

contain excess of free energy proportional to the interfacial area

Surface Tension

Measures the strength of IMFs (Force of pulling on like molecules compared to others)

When its two liquids will try to decrease interface area leading to the formation of spheres to make smallest possible surface area at the given volume.

Emulsions

Dispersion of one liquid into another (immiscible)

Ostwald Ripening

Occurs in water in oil emulsions

Small particles disolve and redeposit onto larger particles gradually over time

Thermodynamically driven process

Creaming

Migration of dispersed particles under influence of buoyancy due to density difference between phases

Coalescence

Two or more particles merge during contact to form a single particle

Aggregation / Floceulation

Formation of clusters in an emulsion

Dispersed particles

Factors in an emulsion breakdown

Droplet size

Concentration

Density

Surface tension

Wine tears

given the lower boiling point of ethanol it will evaporate first leaving just water (increasing surface tension). Evaportates faster on the outsides where thinnest, leading to lots of strong water on the outside. The strong surface tension (pull) of this water pulls up the wine to the side of the glasses until there is enough force from gravity for the collected liquid to fall back down and the process repeats. Marangoni effect.

Emulsifiers

Surface active molecule (surfactants) that absorb at interfaces

lowers the surface free energy and surface tension

Stabilizes the emulsion

Surfactants

Compound that lowers the surface tension between two liquids or between a liquid and a solid.

Amphiphilic organic compounds or polymers

Anionic

contain anionic functional groups at their heats

Cationic

Contain cationic functional groups at their head.

pH dependent primary, secondary, and tertiary amines

permanently charged quartanary

Zwitterionic

Have both cationic and anionic centers attached to same molecule

Non-ionic

Hydrophilicportion not charged (Tweens and Spans)

Tweens

Tend to be soluble or well dispersed in water

HLB = 10 - 19

Spans

Tend to be oil soluble and dispersible or insoluble in water

HLB = 4.7

Polymers

Adsorbs at interface and creates a physicalish barrier to keep things from coming together

HLB System

Emperical scale based on % hydrophonic and hydrophilic functional groups in the molecule

Foams

Dispersion of a gas in a liquidF

Foam Formulation

Supersaturation

Mechanical Force