Water II Flashcards
How do we derive a moisture sorption isotherm?
- Food product is dried completely and then place in an enclosed chamber
- The chamber is above a specific salt solution, each of which generate a specific Aw
- Samples are weighed after they are in equilibrium to determine the amount of moisture absorbed
Aw is directly related to _________ at a constant ________, which is much easier to measure
Equilibrium Relative Humidity (ERH)
temperature
When deriving a moisture sorption isotherm, it is important that the chambers are _________ of known ERH
hermetically sealed
In the derivation of a moisture sorption isotherm, when the sample at equilibrium is weighed, it provides you with information on the _________
equilibrium moisture content
A plot of ___________ vs. ___ or _____ provides the moisture sorption isotherm
equilibrium moisture content
Aw
ERH
The moisture sorption isotherm illustrates how the food product would behave as a function of __________ in terms of water adsorption or loss at a given temperature
relative humidity
Moisture sorption plots are ________ dependent
temperature
In moisture sorption isotherm, ______ commonly occurs when the curve is different dependent on whether the product starts out dry or moist
hysteresis
When does hysteresis occur?
When the curve is different dependent on whether the product starts out dry or moist
Why does hysteresis occur?
Permanent changes in the product (structural/chemical) that have taken place due to changes in moisture content
Except in very simple systems, the moisture sorption curves will show _______.
hysteresis
Moisture sorption information defines how a product picks up or loses _______ under specified conditions (relative humidity).
moisture
What are the uses of the moisture sorption data?
- Determines the final moisture content from a drying operation
- Aw is related to textural changes
- Helps in selection of packaging materials
- Allows the evaluation of effects of compounds that can be used to modify the Aw profile of a product
Moisture sorption data provides important information about the relative stability of a product in regards to what? (2)
- The type of microbial growth possible
- The types of reactions that may predominate in a food system
Which compound may be used to modify the Aw profile of a product?
Sorbitol
Which five factors are a major concern to water activity?
1) Enzymatic reactions
2) Lipid oxidation
3) Hydrolytic reactions
4) Non-enzymatic browning
5) Various forms of microbial growth
Most reactions are _________ functions of water activity
exponential
A slight reduction of water activity will have a significant effect in (increases/reducing) the rate of a reaction
reducing
A break point for many reactions lies around Aw = _____
0.80
Aw has to be reduced down to about ________ to reach a minimum for most of the deteriorative reactions.
0.3-0.4
What is the water activity value/region where all reactions are stopped?
There is none, but the optimum appears to be Aw = 0.3-0.4
What are three ways to control water activity?
- Remove water
- Convert the free water to bound water
- Freeze food
What are the consequences of removing water?
- Can change the physical nature of the food
- Alter its color, texture, and/or flavor
How can you convert free water to bound water?
Addition of sugars, salts, or other water-soluble agents
Freezing _______ the water and (increases/decreases) the Aw
immobilizes
decreases
Should all foods be frozen?
No, not all foods can/should since frozen foods will eventually be thawed
The use of multiple barriers based on Aw, pH, ionic strength, modification of atmosphere, etc. is called the __________ concept
hurdle
What are the two general categories of food systems?
1) Intact edible tissues
2) Food dispersions
_________ refers to natural biological systems (plant and animal tissues), which are very complex
Intact edible tissues
________ refers to complex systems that are usually man-made
Food dispersions
What is a dispersion?
System consisting of one or more discontinuous phases (dispersed) in a continuous system
What are the three types of solutions?
1) True solutions (molecular dispersions)
2) Colloidal dispersions
3) Suspensions
In ________, molecules and ions are present at their lowest subdivision
true solutions
In ________, the particles are <0.1 μm in diameter.
true solutions
In ________ the solution formed is transparent.
true solutions
In ________, the solution has high osmotic pressure
true solutions
In ________, the solution passes through parchment membranes
true solutions
If the solution does not pass through a parchment membrane but does
not settle under the force of gravity, it is considered to be __________
colloidal
__________ are usually a macromolecule or an aggregate of a smaller molecule, with a size range of 0.1 - 1 um
Colloids
In ________, the solution has significantly reduced osmotic pressure
colloids
In _______, the may be transparent but is often translucent - scatters light.
colloids
True _______ solutions do not settle out of solution and may aggregate to form gels
colloid
_________ are generally opaque, and suspended material can be
filtered out, or settle-out with time
Suspensions
________ show negligible or no measurable osmotic pressure
Suspensions
Place the three solutions in order of their particle size (smallest to largest):
True solutions < Colloids < Suspensions
Ungelatinized starch granules will form a _______ when stirred, but soon settle out.
suspension
Gelatinized starch forms a ___________ or gel depending on concentration.
colloidal solution
True solutions are considered to be ______ systems, while colloidal solutions and suspensions are considered to be _______ systems.
uniphasic
biphasic
The conversion of a true molecular solution to a colloidal solution often takes place when ____________ are involved.
macromolecules
If the overall __________ (which depend on pH) are not too great, macromolecules can associate via various mechanisms
charge repulsions
Particles can be built up which eventually obtain enough charge to prevent further association and will stay stable in a _______ form in solution.
colloidal
Wastewater from food processing plants often contains substantial amounts of ______ material
colloidal
a common method of wastewater treatment is to convert these _______ solutions into _________ that will settle out by adding salts to neutralize the charge of the colloids
colloidal
suspensions
The formation of colloids is the result of what? (4)
- Electrostatic interactions
- Hydrogen bonding
- Hydrophobic interactions
- Hydrophobic/hydrophilic associations
The formation of colloidal solutions via _________________________ is the basis of many common food dispersions:
hydrophobic/hydrophilic associations
A liquid in a liquid forms an ________
emulsion
A gas in a liquid forms a ________
foam
A liquid in a solid forms a ___________
solid emulsion
A gas in a solid forms a __________
solid foam
Both ______ and _______ involve the dispersion of a hydrophobic material in a hydrophilic material or vice versa.
emulsions
foams
______ and _______ are unfavorable from a free energy standpoint
Emulsions
foams
High __________/__________ can be reduced by _______ or ________ via hydrophobic/hydrophilic associations.
intersurfacial tension
surface tension
emulsifiers
surfactants
Any compound that has both hydrophilic and hydrophobic groups in its molecular structure usually has the property of being a ____________ agent, more commonly termed a ________.
surface-active
surfactant
All _________ have the property of reducing the surface tension of water significantly, causing foaming, and can form emulsions.
surfactants
_______ is the equivalent for surfactants in terms of food applications
Emulsifiers
When emulsifiers or surfactants are dissolved in water, they (are/are not) uniformnly distributed in a molecular solution
are not
Initially, emulsifiers and surfactants are found to be near the solution’s _________
surface
Air-water interface is the location of the lowest __________ for emulsifiers and surface-active compounds
free energy state
The hydrophobic ends orient themselves toward ________ air, while the ________ ends will orient themselves into the water.
hydrophobic
hydrophilic
The reorientations of emulsifiers and surfactants (increases/reduces) the surface tension of water
reduces
Emulsifiers and surfactants are capable of forming colloid-like particles called ______
micelles
If the concentration of an emulsifier or surfactant added to a solution is increased beyond the surface-covering capacity, then _______ are formed in the solution.
micelles
Micelles form so as to reduce the free energy of the solution after the air/water interface has been ________.
saturated
The rapid decrease in surface tension represents the surfactant molecules going to the ________ of the liquid.
surface
After micelle formation, how does the surface tension change with increased surfactant concentration?
Does not change significantly
Phospholipids and monoglycerides can be used as _______
emulsifiers
Emulsions (increases/decreases) the viscosity of a system
increases
The opacity of an emulsion is a function of the __________ of the dispersed phase, which is a function of the _______ put into the system.
droplet size
energy
What is the size of a droplet size which can distinguish phases?
Macroglobules (> 1 um)
What is the size of a droplet size which is milky white?
1 um
What is the size of a droplet size which is bluish white?
1 um - 0.1 um
What is the size of a droplet size which is gray-semitransparent white?
0.1 um - 0.05 um
What is the size of a droplet size which is clear?
< 0.05 um
What are the two basic categories of emulsifiers?
- Non-ionic
- Ionic
_______ emulsifiers are the most important and widely used group because they are insensitive to ______
Non-ionic
pH
What are the three types of non-ionic emulsifiers?
1) Emulsifiers based on glycerol esters and their non-charged derivatives
2) Sorbitan derivatives
3) Esters of polyhydric compounds
The use of emulsifiers ______________ began when glycerol was added to fats with a small amount of base to interesterify the fat to produce some ________
based on glycerol esters
monoglycerides
Emulsifiers based on glycerol esters were termed __________, and contained __% monoglycerides
superglycerinated shortening
3
_________ greatly enhanced cake volume, especially with high sugar levels
Emulsifiers based on glycerol esters (non-ionic emulsifiers)
Nowadays, pure monoglycerides/diglycerides are manufactured by ____________ followed by ____________ to obtain relatively pure fractions.
interesterification
fractional distillation
Fatty acid composition of monoglyceride affects its properties, and its plasticity is controlled by its overall __________
iodine value
___________ monoglycerides have IVs of 19-36, while __________ have IVs of 65-67.
Dry powdered
plastic emulsifiers
