2. Mixtures: Solutions, Colloidal Dispersions, and Suspensions22
Mixtures: Solutions, Colloidal Dispersions, and Suspensions

3. Objectives
List the factors that affect the solubility of one substance in another.
Calculate the mass percent of solute in a solution.
Compare colloids and solutes.
Differentiate between the two most common types of food emulsions.
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4. Objectives
Describe factors that can affect the stability of a food foam.
Explain the properties of suspensions using batters and doughs as examples.

5. Mixtures
Most foods are complex mixtures of many types of elements and compounds
Understanding how components interact helps predict how foods will react during processing
The dispersed phase refers to the particles scattered throughout the medium
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6. Mixtures
The continuous phase is the medium in which particles are distributed
Food mixtures are classified by the size of particles distributed throughout the mixture
Solutions have the smallest particles
Colloidal dispersions have particles larger than those in solutions
Suspensions have the largest particles

7. Solutions A solution is a homogenous mixture of 2 or more substances
The dispersed phase is the solute
The continuous phase is the solvent
Particles are small and have a high level of kinetic energy
Solutions cannot form gels
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8. Solutions
Solutions are possible in any combination of the 3 states of matter
The most common types of solutions are
solids in liquids (salt or sugar in water)
liquids in liquids (flavorings and vinegars)
gas in liquids (carbonated beverages)

9. Factors Affecting Solubility
Solubility describes the amount of solute that will dissolve in a solvent
Le Chatelier’s principle states that when the chemical equilibrium changes, the equilibrium shifts to counteract the change
Solubility is affected by
temperature, particle size, concentration, pH, agitation, and vapor pressure

10. Factors Affecting Solubility: Temperature
The solvent’s temperature affects the solubility of solids
The amount of solid solute that a solvent will hold increases as temperature increases
A solid dissolves faster if more molecules of a solvent collide with molecules of the solid
In candy production, as water heats it can hold more sugar solute
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11. Factors Affecting Solubility: Temperature
The solvent’s temperature affects the solubility of gases
The amount of gaseous solute that a solvent holds decreases as temperature increases, which is why soft drinks lose their carbonation faster at room temperature
The more the gas molecules move, the less energy it takes for the gas to escape

12. Factors Affecting Solubility: Particle Size
The smaller the solute’s particles are, the greater is the exposed surface area and the faster the solute will dissolve
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13. Factors Affecting Solubility: Concentration
Concentration is the measure of parts of one substance (solute) to the known volume of another (solvent)
A solution that can dissolve more solvent at a given temperature is unsaturated
A solution holding all the solute that will dissolve in a solvent at any given temperature is saturated
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14. Factors Affecting Solubility: Concentration
Intermolecular bonding plays a key role
Hydrogen bonds form when water comes close to other polar molecules
When all water molecules have bonded to a solute, a solution is at the saturation point
Heat breaks bonds in the solute, allowing the solution to hold more solute
If the solution is heated then cooled, a supersaturated solution forms

15. Factors Affecting Solubility: pH
Singly charged ions tend to be more soluble than ions with 2 or more charges
Smaller ions are more soluble than larger ions
Calcium carbonate, a compound used in calcium supplements, dissolves slowly in neutral water, but more quickly when an acid is added

16. Factors Affecting Solubility: Agitation
Agitation or stirring speeds the dissolving rate until the saturation point is reached
Agitation also adds a small amount of energy that slightly raises the temperature
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17. Factors Affecting Solubility: Vapor Pressure
Vapor pressure is
the pressure at which gases escape from and dissolve into a liquid at the same rate
important in maintaining gases in solution
Gas concentration in a liquid directly relates to pressure of the gas over the liquid
Fizz in carbonated drinks occurs because gas is added to liquid under pressure

18. Measuring Solute Concentrations
Mass percent is the percentage of the mass in a solution that comes from the solute
The mass of the solute is divided by the total mass of the solution and multiplied by 100
mass of solute
mass of solution
x 100 = mass percent
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19. Measuring Solute Concentrations
When solutes are added to water, the freezing point drops and boiling point rises
The change is greater as the mass percent of the solute increases
Solutes containing ionic bonds will produce solutions with even lower freezing points and higher boiling points
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20. Measuring Solute Concentrations
Effects of solutes on the freezing point is demonstrated in making ice cream
Sugar and milk solids (solutes) cause the ice cream solution to have a lower freezing point
Surrounding the ice cream solution in a metal can is ice that melts when salt is added
The saltwater solution has a lower freezing point than does the ice cream mixture
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21. Measuring Solute Concentrations
These steps finish the ice cream example
Heat energy is transferred from the ice cream mixture to the saltwater solution
As the ice cream mixture loses heat energy, its temperature drops, allowing it to freeze
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22. Measuring Solute Concentrations
As the mass percent of a solute increases, the solution’s vapor pressure increases
Pressure is equalized by either absorbing water or allowing solutes to escape
Molecules move in the direction with the least resistance
Soft drinks fizz after opening the container until vapor pressure is reached

23. Applications in the Beverage Industry
To make carbonated beverages
water is treated to yield consistent quality
sweeteners, flavorings, coloring agents, acids, and carbon dioxide are the solutes
carbohydrate gums or pectins give diet drinks the mouthfeel of sweetened drinks
acids act as flavor enhancers and preservatives
sodium benzoate is usually added as a preservative
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24. Applications in the Beverage Industry
Soft drinks sold at restaurants and refreshment stands are made with a concentrated syrup added to water
Coffee and tea are solid solutes in water
Their production is complex, involving roasting times, particle sizes, and flavoring agents
Brewing time and temperature impact strength and flavor

25. Colloidal Dispersions
Colloidal dispersions are mixtures in which microscopic particles of one substance are evenly distributed in another
The particles, which are not dissolved, give the mixture its unique characteristics
The 3 types of colloidal dispersions are
emulsions, foams, and gels

26. Characteristics of Colloid Dispersions
Colloid dispersions have a
continuous phase, which is the medium that holds the dispersed particles
dispersed phase, which contains particles called colloids distributed throughout
Examples are jelly, mayonnaise, and gelatin
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27. Characteristics of Colloid Dispersions
Colloids are up to 1,000 times larger than solute particles
Solute particles are up to 1 nanometer (nm)
Colloids are between 1 nm and 1,000 μm
Solute particles dissolve in other substances
Colloids do not dissolve, but can be dispersed in another substance
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28. Characteristics of Colloid Dispersions
When light rays pass through a colloidal dispersion
they scatter and become visible, causing a phenomenon called the Tyndall effect
When light rays pass through a solution
no change in the direction of the light ray is visible because solutes are too small to bend light
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29. Characteristics of Colloid Dispersions
The motion of the molecules in the continuous phase causes collisions that keep the colloids dispersed
Colloids of the same substance have the same electrical charge
This causes them to repel each other and water molecules to align around the colloid
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30. Characteristics of Colloid Dispersions
If particles are denser in the continuous phase, they will sink as a mixture sits
Most colloids in foods are starches and proteins, which form colloid dispersions when the molecular structure changes
If particles of the dispersed phase are less dense than the continuous phase, they will rise to the top of the mixture
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31. Characteristics of Colloid Dispersions
Milk is an example of a colloidal dispersion
Lactose and mineral salts are solutes
Proteins are colloids
Fat is in suspension
Milk undergoes homogenization to keep fat suspended
If untreated, fat (cream) would rise to the top

32. Emulsions
An emulsion is a mixture of 2 immiscible liquids, where one is dispersed in droplet form in the other
Usually one liquid is polar in nature, such as vinegar, and the other is nonpolar, such as oil
The liquids separate because the molecules repel or move away from each other
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33. Emulsions
Temporary emulsions are unstable mixtures of a polar and a nonpolar liquid
As the mixture stands, liquids will separate
A permanent emulsion needs an emulsifier to stabilize the mixture
It has a polar end and a nonpolar end
Lecithin found in egg yolks is an example
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34. Emulsions Oil-in-water emulsions include
mayonnaise, salad dressings, and cake batters
Water-in-oil emulsions include
butter, made from whipping cream having fat globules surrounded by phospholipid membranes containing lecithin
margarine, made by vigorously mixing its fat- and water-soluble ingredients together

35. Factors Affecting Emulsion Stability: Temperature
Thermal conductivity, or the ability to conduct heat energy, will impact emulsions
Because water conducts heat energy faster than fat, an oil-in-water emulsion will freeze faster than a water-in-oil emulsion
High temperatures will destabilize emulsions when the emulsifier is a protein

36. Factors Affecting Emulsion Stability: Electrical Charge
Emulsions are stable because of the electrical attraction between water and the polar end of the emulsifier
Running an electric current through an emulsion will destabilize it
This principle can be used to separate parts of emulsions

37. Ice Cream as an Emulsion
Ice cream is a water-based sugar solution that forms an emulsion with fat-based cream
As the water freezes, the sugar concentration rises and reaches the saturation point, at which time sugar begins to settle out as crystals, possibly forming a gritty texture
Gums, pectins, and lecithin are the emulsifiers that prevent crystallization

38. Foams
Foams are colloidal dispersions of gas or air bubbles in a liquid
Foam on root beer and soft drinks is an unstable foam
Whipped cream and meringue are stable foams
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39. Foams Keeping a foam stable requires 4 conditions
The liquid must be viscous enough to trap and hold air
A stabilizer must be present that stretches and forms a thin film around bubbles
The surface tension of the film should be less than that of water
The liquid must have a low vapor pressure

40. Factors Affecting Foam Stability: Temperature
Whipping cream
develops the best foam when it, the bowl, and beaters are well chilled because the viscosity of fat is greater when cool
Egg white
reaches the fullest volume of foam when left at room temperature for a half hour before beating

41. Factors Affecting Foam Stability: Adding Solutes
Sugar must be added at the right point to produce the most stable foam
Generally this is after a foam begins to form but before it reaches the soft peak stage
Adding sugar
before a foam forms can delay foam formation
after a foam completely forms will cause a coarse texture

42. Factors Affecting Foam Stability: Acidity
Whipping cream forms the best foam
when fresh because bacteria lower the pH with aging and change lactose to lactic acid
Egg white forms the best foam when
eggs are fresher and have a lower pH, between 7.0 and 8.0
cream of tartar is used to further lower pH to 4.6 and 4.8

43. Factors Affecting Foam Stability: Fat
Fat reduces protein’s foaming ability to form a film around air bubbles
Eggs should be separated carefully so no egg yolk accidentally mixes into the whites
The bowl and beaters should be clean
Avoid using plastic bowls that may contain traces of fat from previous mixtures due to their porous nature

44. Suspensions
A suspension is a mixture of undissolved particles in a liquid
It can be very unstable due to the size of the dispersed particles
The continuous phase must be viscous enough to keep the particles from floating or sinking
The larger the particles, the more viscous the continuous phase must be to maintain stability
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45. Suspensions Examples of suspensions are fruit pieces in gelatin
crushed berries in ice cream
spices and herbs in Italian dressing
©Charles Brutlag/Shutterstock.com
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46. Suspensions Batters Doughs
are pourable mixtures with pieces suspended throughout
have air bubbles to provide leavening, resulting in a light, airy baked product
Doughs
have a higher proportion of flour so they can be shaped rather than poured
keep large particles evenly suspended

47. Recap
Factors that affect the solubility of one substance in another are
temperature
particle size
concentration of the solution pH
agitation
vapor pressure
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48. Recap A measure of concentration of a solution is the mass percent
Solute concentration affects freezing point, boiling point, and vapor pressure
Colloid dispersions are mixtures where particles are dispersed without being dissolved
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49. Recap
The 2 most common types of food emulsions are oil-in-water and water-in-oil
Factors that affect the stability of a food foam are
temperature, the addition of a solute, acidity, and fat content
Batters and doughs form the continuous phase of some food suspensions