Chapter 22: Mixtures: Solutions, Colloidal Dispersions, and Suspensions Flashcards
Most foods are complex mixtures of what?
Most foods are complex mixtures of many types of elements and compounds
- understanding how components interact helps predict how foods will react during processing
What is the Dispersed Phase?
refers to the particles scattered throughout the medium
What is the Continuous Phase?
is the medium in which particles are distributed
How are Food Mixtures classified?
Food Mixtures are classified by the size of particles distributed throughout the mixture
How big are the particles in solutions?
Solutions have the smallest particles
How big are the particles in Colloidal Dispersion?
Colloidal Dispersions have particles larger than those in solutions
How big are the particles in Suspensions?
Suspensions have the largest particles
What is a solution?
A solution is homogenous mixture of 2 or more substances
- The dispersed phase is the solute
- The continuos phase is the solvent
- Particles are small and have a high level of kinetic energy
- Solutions cannot form gels
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 (flavouring and vinegars)
- Gas in Liquids (carbonated beverages)
What is Solubility?
Solubility describes the amount of the solute that will dissolve in a solvent
What is Le Chatelier’s Principle?
states that when the chemical equilibrium changes, the equilibrium shifts to counteract the change
Solubility is affected by what?
temperature, particle size, concentration, pH, agitation and vapour pressure
The solvents temperature affects the solubility of solids by..?
- The amount of solid solute that a solvent will hold increases as temperature increases
- A solid dissolves faster if more molecules of the solid
- In candy production, as water heats it can hold more sugar solute
The Solvents 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
The smaller the solute’s particles are, the greater what?
The smaller the solute’s particles are, the greater is the exposed surface area and the faster the solute will dissolve
What is Concentration?
concentration is the measure of parts of one substance (solute) to the known volume of another (solvent)
What does unsaturated mean?
A solution that can dissolve more solvent at a given temperature is unsaturated
What does saturated mean?
A solution holding all the solute that will dissolve in a solvent at any given temperature is saturated
Intermolecular bonding plays a key role in concentration by..?
- Hydrogen bonds form when water comes close to other polar molecules
- Heat breaks bonds in the solute, allowing the solution to hold more solute
What is a saturation Point?
When all water molecules have bonded to a solute, a solution is at the saturation point
What does Supersaturated solution mean?
If the solution is heated then cooled, a supersaturated solution forms
Singly charged ions tend to be more what?
Singly charged ions tend to be more soluble than ions with 2 or more charges
Smaller ions are more what?
Smaller ions are more soluble than larger ions
- Calcium carbonate, a compound used in calcium supplements, dissolves slowly in neutral water, but quickly when an acid is added
How does Agitation affect Solubility?
Agitation or stirring speeds the dissolves rate until the saturation point is reached
- Agitation also adds a small amount of energy that slightly raises the temperature
How does Vapour Pressure affect solubility?
Vapour pressure is
- The pressure at which gases escape from and dissolves into a liquid at the same rate
- Important in maintaining gases in solution
Gas concentration in a liquid directly relates to what?
Gas concentration in a liquid directly relates to pressure of the gas over the liquid
Fizz in carbonated drinks occurs because of what?
Fizz in carbonated drinks occurs because gas is added to liquid under pressure
What is 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 multiplied by 100
(mass of solute/mass of solution X100) = mass percent
When solutes are added to water what happens?
When solutes are added to water, the freezing point drops and boiling point rises
- The change is greater as the mass percent of solute the solute increases
Solutes containing ionic bonds will produce what?
Solutes containing ionic bonds will produce solutions with even lower freezing points and higher points
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 lower freezing point than does the ice cream mixture
What 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
As the Mass percent of a solute increases what also increases?
As the mass of a solute increases, the solution’s vapour 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 vapour pressure is reached
How do you make carbonated beverages?
- Water is treated to yield consistent quality
- Sweeteners, flavourings, colouring agents, acids and carbon dioxide are solutes
- Carbohydrate gums or pectins give diet drinks the mouthfeel of sweetened drinks
- Acids act as flavour enhancers and preservatives
- Sodium benzoate is usually added as a preservative
Soft drinks sold at restaurants and refreshment stands are mad with what?
They are made with a concentrated syrup added to water
What are Coffee and Teas?
Coffee and Tea are solid solutes in water
- Their production is complex, involving roasting times, particle sizes, and flavouring agents
- Brewing time and temperature impact strength and flavour
What is Colloidal Dispersion?
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
What are the 3 types of colloidal dispersions?
- Emulsions
- Foams
- Gels
What are some characteristics of Colloid Dispersions?
- Continuous phase, which is the medium that holds the dispersed particles
- Dispersed, which contains particles called colloids disturbed throughout
ie) jelly, mayonnaise, and gelatin
Colloids are up to how many times larger than solute particles?
Colloids are up to 1000 times larger than solute particles
- Solute particles are up to 1 nanometer (nm)
- Colloids are between 1nm and 1000um
Solute particles dissolve in other substances and colloids do what?
Colloids do not dissolve, but can be dispersed in another substance
What is the Tyndall Effect?
When light rays pass through a colloidal dispersion, they scatter and become visible, causing a phenomenon called the Tyndall effect
What happens 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
The motion of molecules in the continuous phase causes what?
The motion of the molecules in the continuous phase cause collisions that keep the colloids dispersed
Colloids of the same substance have what?
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
What happens if particles are denser in the continuous phase?
They will sink as the mixture sits
Most colloids in foods are what?
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, what will happen?
They will rise to the top of the mixture
Milk is an example of what?
Milk is an example of colloidal dispersion
- Lactose and mineral salts are solutes
- Proteins are colloids
- Fat is in suspension
Milk undergoes what to keep fat suspended?
Milk undergoes homogenization to keep fat suspended
- If untreated, fat (cream) would rise to the top
What is an Emulsion?
is a mixture of 2 immiscible liquids, where one is dispersed in droplet forms in the other
- Usually one liquid is polar in nature and the other is nonpolar
- The liquids separate because the molecules repel or move away from each other
What are Temporary Emulsions?
are unstable mixtures of a polar and a nonpolar liquid
- as the mixture stands, liquids will separate
What is an Emulsifier?
A permanent needs an emulsifier to stabilize the mixture
- It has a polar end and a nonpolar end
- Lechithin found in egg yolk is an example
What are Oil-in-Water emulsions?
mayonnaise, salad dressings and cake batters
What are water-in-oil emulsions?
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
What is Thermal Conductivity?
or the ability to conduct heat energy, will impact emulsions
- Because water conducts heat energy faster than water-in-oil emulsions
- High Temperatures will destabilize emulsions when the emulsifier is a protein
Why are emulsions stable?
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 do what to it?
It will destabilize it
- This principle can be used to separate parts of emulsions
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
What are 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
Keeping a foam stable requires 4 conditions?
- 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 vapour pressure
How does temperature affect Whipping Cream foam?
develops the best foam when it, the bowl and beater are well chilled because the viscosity of fat is greater when cool
How does temperature affect Egg whites foam?
reaches the fullest volume of foam when left at room temperature for half hour before beating
Sugar must be added at the right point to produce the most stable foam, what point is this?
Generally this is after a foam begins to form but before it reaches the soft peak stage
Adding sugar before a foam forms can do what?
Can delay foam formation
Adding sugar after a foam completely forms will cause what?
Will cause a coarse texture
Whipping cream forms the best foam when?
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 and 9
2. Cream of tartar is used to further lower pH to 4.6 and 4.8
Fat reduces a proteins foaming ability to form a film around air bubbles by…?
- 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
What is a Suspension?
is a mixture of undissolved particles in a liquid
- It can be very unstable due to the size of the 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
What are some examples of suspensions?
- Fruit pieces in gelatin
- Crushed berries in ice cream
- Spices and herbs in Italian dressings
What are Batters (Suspension)?
Are pourable mixtures with pieces suspended throughout
- have air bubbles to provide leavening, resulting in a light, airy baked product
What are Doughs (Suspensions)?
Have a higher proportion of flour so they can be shaped rather than poured
- Keep larger particles evenly suspended
