Water - Summary Flashcards
What are the three methods to reduce the water activity of a system?
- Freezing
- Concentration
- Dehydration
Oxygen has ___ electrons, ___ of which are valence electrons, and the two hydrogens have ___ electrons each
8
6
1
What combines to form four sp^3 hybrid orbitals?
- Three 2p orbitals
- One 2s orbital
Only ___ of oxygen’s ___ valence electrons are used up in the two covalent bonds that form between H and O
2
6
There are ___ oxygen lone electron pairs left in ____ of the sp3 orbitals
2
2
In the liquid phase, water is considered to have “_________” structure, termed ”__________”
transitional
flickering clusters
Flickering clusters (do/don’t) exist at the boiling point of water
do
The formation of bulky hydrates generally causes an (increase/decrease) in viscosity and tends to (increase/decrease) the freezing point of the system.
increase
decrease
When low concentrations of nonpolar substances are dissolved in water, __________ are induced.
ice-like inclusions
The formation of an __________ around a nonpolar group or molecule is to (maximize/minimize) the free energy state of the system when symmetric electron-neutral constituents (hydrophobic) and asymmetric electron-rich hydrophilic materials are forced to associate.
ice-like structure minimize
The semi-crystalline form of ice-like inclusions are termed “______________”
clathrate hydrates
Define clathrate compounds (important).
- Compounds which are not formed by the action of valence bonds, but by molecular imprisonment
- Host molecule: water
- Guest: non-polar gas or liquid
In the freezing of water, the flickering cluster becomes a _________ or ________, due to a decrease in _______
minute crystal
nucleus
kinetic energy
At 0oC there is an equilibrium between __________ and liquid water.
crystal nucleation
In ultrapure water, _______ is difficult and does not readily take place
nucleation
In ultrapure water, _______ can occur when the water stays liquid well below 0oC
supercooling
When the eutectic point has been reached, all the water in the system is ___________.
immobilized
Type ____ water contains some solutes but not enough to immobilize the water in any
major way.
III
In type ____ water, many microorganisms are capable of growth, with some bacteria and yeasts inhibited at the lower end of the range.
III
In type ___ water, most hydrolytic, oxidative, and enzymatic reactions proceed readily in this water activity range.
III
Is the freezing point of water depressed in type III water?
Not significantly
Type ___ water is the water present in macrocapillaries
III
Type ___ water is broad-range water present in microcapillaries to the outer layers of “bound water”
II
In type ____ water
most microbial growth is halted, with the exception of some molds at the upper end of this range.
II
In type ____ water , the freezing point of water is significantly reduced and most enzymatic reactions requiring water are slowed significantly
II
In type II water, non-enzymatic browning takes place with heat at the (upper/lower) range, and without heat at the (upper/lower)
upper
lower
Type ___ water is essentially immobile
I
In type I water, most reactions are minimal with the exception of ________
autoxidation
______ occurs when a wet food is placed in a dry environment
Desorption
Differentiate desorption and dehydration.
Desorption: food is moving towards equilibrium with the environment
Dehydration: permanent loss of
________ occurs when a dry food is placed in a wet environment
Adsorption
A plot of ___________ vs. ___ or _____ provides the moisture sorption isotherm
equilibrium moisture content
Aw
ERH
In moisture sorption isotherm, ______ commonly occurs when the curve is different dependent on whether the product starts out dry or moist
hysteresis
Which compound may be used to modify the Aw profile of a product?
Sorbitol
Aw has to be reduced down to about ________ to reach a minimum for most of the deteriorative reactions.
0.3-0.4
The use of multiple barriers based on Aw, pH, ionic strength, modification of atmosphere, etc. is called the __________ concept
hurdle
_________ refers to natural biological systems (plant and animal tissues), which are very complex
Intact edible tissue
In ________, the solution has high osmotic pressure
true solutions
In ________, the solution has significantly reduced osmotic pressure
colloids
True _______ solutions do not settle out of solution and may aggregate to form gels
colloid
________ show negligible or no measurable osmotic pressure
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
A liquid in a liquid forms an ________
emulsion
A gas in a liquid forms a ________
foam
______ and _______ are unfavorable from a free energy standpoint
Emulsions
foams
Air-water interface is the location of the lowest __________ for emulsifiers and surface-active compounds
free energy state
The reorientations of emulsifiers and surfactants (increases/reduces) the surface tension of water
reduces
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
Emulsions (increases/decreases) the viscosity of a system
increases
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 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
Emulsifiers based on glycerol esters were termed __________, and contained __% monoglycerides
superglycerinated shortening
3
___________ monoglycerides have IVs of 19-36, while __________ have IVs of 65-67.
Dry powdered
plastic emulsifiers
_____________ are produced by treating monoglycerides with ethylene oxide
Polyoxyethylene monoglycerides
Treating monoglycerides with ethylene oxide leads to the polymerization of ethylene oxide as well as the connection of the polymer to the ____ group at either the __ or ___-position on the glycerol bacbone
OH
2
3
What are other derivatives of emulsifiers based on glycerol esters?
- Lactylated monoglycerides
- Propylene glycol esters
________ are produced by the reaction of sugar alcohol with stearic acid in the presence of a catalyst
Sorbitan derivatives
_______ are a sugar alcohol esterified to a fatty acid
Sorbitan derivatives
Polyglycerol derivatives and sugar esters qualify as esters of _________
polyhydric compounds
Olestra is _________ esterified with _______ fatty acids
sucrose
6-8
What are the three categories within the ionic emulsifiers?
- Anionic (-)
- Amphoteric (+/-)
- Cationic (+)
________ emulsifiers are charged monoglyceride derivatives
Anionic
The most important anionic monoglyceride emulsifier is ___________, produced by the reaction of a monoglyceride with ________
succinylated monoglyceride (SMG) succinic anhydride
Sodium stearoyl-2-lactylate is an example of a non-glycerol-base _______ emulsifier
anionic
_________ forms very stable oil-in-water emulsions, which are very resistant to freeze/thaw cycles (good for frozen food)
sodium stearoyl-2-lactylate
The chief use of the ______ emulsifier ____________ is as a whipping aid for egg whites
anionic
sodium lauryl sulfate
How is sodium lauryl sulfate produced?
- Reduction of coconut oil fatty acids to their alcohols
- Followed by sulfonation of the alcohols produced
Why are cationic emulsifiers not used as food additives? What are they used as instead?
- Bactericidal/toxic
- Potent surface-active agents –> cleaning products
Quaternary ammonium compounds are examples of ______ emulsifiers
cationic
Phosphatidylinositol is ________
anionic
Phosphatidylcholine is ________
amphoteric
Phosphatidylethanolamine is ________
amphoteric
What does bleaching of lecithin cause structurally?
Produces hydroxyl groups at the sites of fatty acid unsaturation
What is the effect of hydroxylated lecithin?
More dispersible in cold water and is a more effective emulsifier than lecithin itself
What are hydrocolloids generally made of?
Polysaccharides (starch and gums)
________ are a group of compounds often used in conjunction with emulsifiers
Hydrocolloids
Are hydrocolloids emulsifiers?
No, they are termed stabilizing agents
What is the major contribution of hydrocolloids?
Enhancement of the viscosity of the hydrophilic phase (continuous phase)
What is the role of gums?
Form films around oil emulsion droplets
The HLB system is mainly applicable to _______ emulsifiers
non-ionic
The HLB value represents the weight percentage of ________ groups in a non-ionic emulsifier molecule divided by ____
hydrophilic
5
What is a completely lipophilic HLB value?
0
What is a completely hydrophilic HLB value?
100/5 = 20
What does an HLB of 1-6 promote?
- Hydrophobic
- Promotes water-in-oil emulsions
What does an HLB of 12-20 promote?
- Hydrophilic
- Promotes oil-in-water emulsions
______ have an HLB range of 15-18
Solubilizers
_______ have an HLB range of 13-15
Detergents
______ have an HLB range of 7-9
Wetting agents
Emulsifiers as __________ allow more use of non-wheat proteins
conditioners
