Water and Food Dispersions Flashcards
What are 3 common roles of water in food systems?
- A carrier of nutrients and wastes
- A reactant and a reaction medium
- A stabilizer of biopolymer configuration (poteins and COHs)
Water makes up what % of tomatoes and lettuce?
95
Water makes up what % of apple juice/milk?
87
Water makes up what % of potatoes?
78
Water makes up what % of meats?
65-70
Water makes up what % of bread?
35
Water makes up what % of honey?
20
Water makes up what % of rice/wheat flour?
12
Water makes up what % of shortening?
0
The amount of water, its location and its interaction with the chemical components in a food product is extremely important from the standpoint of _________and ________.
- acceptability
2. STABILITY
What is texture often associated with? Example?
Moisture
Ex: freeze-dried orange vs. fresh orange
Because water is a major reactant and serves as a reaction medium, many of our food processing and preservation methods involve the control of water content to:
slow down deteriorative reactions
What 3 factors all reduce the water activity (Aw) of a system?
- Freezing
- Concentration
- Dehydration
What is one of the most abundant molecular species on Earth?
Water
Water is the only _____ liquid and the most _______ solid.
- common
2. abundant
Comparing water (hydrate of oxygen) to the hydrates of other atoms:
a) Across the periodic table (CH4, NH3, HF - all ____ at room temp)
b) Down the periodic table (H2S, H2Se, H2Te - all _____)
Gases
How many electrons does H2O have? How many are valence? How many electrons does each Hydrogen have?
8, 6, 2
The __ __ orbital(s) and the __ __ orbital(s) of the oxygen atom are combined to form __ __ _____ orbitals.
- three 2p
- one 2s
- four sp3 hybrid
How many of oxygen’s 6 valence electrons are used up in the two covalent bonds that form between H and O? What is the net result?
2
Net result: there are 2 oxygen lone electron pairs left in two of the sp3 orbitals
What makes oxygen highly electronegative in a water molecule?
Its 2 lone electron pairs
Water molecules can be viewed as having two ________ regions and two ________ regions situated ________.
- electron-rich
- electron-poor
- tetrahedrally
In the presence of other water molecules, the electron-rich/poor regions of H2O will associate in order to do what?
To minimize the overall free energy of the system.
What is hydrogen bonding?
The associations due to differential electron density between hydrogen and other electronegative atoms
The tetrahedral nature of the spatial arrangement of these regions of electron density in H2O molecules promotes the ability to form a _________________.
3D association/network
How strong are hydrogen bonds? Is this strong?
~10 kcal/mol
Not very strong
Hydrogen bonding is the basis for what in the atmosphere? What does this lead to?
Water vapor accumulation. Leads to the accumulation of clouds
What is capable of forming due to waters ability to hydrogen bond in 3D?
local regions of structure
What structure does water have in the liquid phase? What is this termed?
“Transitional” structure
Termed: “flickering clusters”
What do flickering clusters do?
They continually form and break up
What is the lifetime of flickering clusters?
10^-10 to 10^-11 seconds
What happens to the # of flickering clusters as the tempurature of water increases? What is simultaneously happeing to the number of molecules per cluster?
Increases
Decreases
Do flickering clusters still exist at the boiling point of water?
yes
What have flickering clusters been postulated to explain?
The relatively normal (low) viscosity of water.
All ______ affect the “structure” of water to some exten
solutes
What happens when ionic compounds are dissolved in water? What is this due to?
The ionize into their respective ions.
Due to the very polar nature of water molecules
Is the polarity of water sufficient enough to break covalent bonds?
No
The polarity of water molecules can dissociate ____ bonds by allowing multiple water molecules to act as ______ for opposing charged ionic species
- ionic
2. counterions
What happens to the ions of NaCl as it is dissolved in water?
Each ion is hydrated by water
When NaCl dissolves in water, what is attracted to the chlorine anions? The sodium cations?
Slightly + hydrogen
Slightly negative oxygen
When NaCl is dissolved in water, what forms around each ion? What does this do?
A hydration shell.
This NEUTRALIZES the charge of the respective ions.
What does the formation of hydration shells around the solute do? What does this do to the normal structure of water?
It forces water into a specific orientation around each ion. This disrupts the normal structure of water.
How does the formation of bulky hydrates affect viscosity of the system?
Increases viscosity
How does the formation of bulky hydrates affect the freezing pt. of the system?
Depresses the freezing pt.
Hydrogen bonding compounds are capable of __________ the structure of water.
Disrupting
Water around a hydrogen bonding site on a molecule will associate in a manner that disrupts what?
the natural tetrahedral geometry of water.
Can hydrogen bonding solutes disrupt the structure of water?
yes
Which macromolecules have a large number of hydrogen bonding sites?
polypeptides, proteins, carbohydrates, and polysaccharide
What can happen to water when exposed to macromolecules that have a large number of H-bonding sites? Under what condition?
The water can be completely/extensively immobilized by hydrogen bonding if the amount of water present is limited.
When ____ concentrations of non-polar substances (hydrocarbons, FAs, or nonpolar side chains of proteins) are dissolved in water, ______ are thought to be formed.
- low
2. ice-like inclusions
How does the formation of ice-like structures around a non-polar group/molecule affect free energy? Why?
Minimizes the free energy state of the system. Because symmetric electron-neutral constituents (hydrophobic) and asymmetric electron-rich hydrophilic materials are forced to associate.
What form does an ice-like inclusion produce? What is another term for this? Is it structurally identical to ice?
Semicrystalline.
Clathrate hydrates
No
What is the definition of Clathrate compounds?
Compounds not formed by the action of valence bonds but by molecular imprisonment
Clathratehydrate structures are important in stabilizing ________ structure around ________ moieties
Protein
Hydrophobic
Overall, the presence of any solute will tend to have a ______ effect on the structure of water.
disruptive
In all cases, the activity of water (its freedom of movement) is ______ when a solute is added
Reduced
When does the freezing or crystallization of water take place?
When the kinetic energy of the molecule is reduced to such an extent that a flickering cluster is able to become large enough to form a MINUTE CRYSTAL OR NUCLEUS.
What happens to water at 0 degrees celcius?
There is an equilibrium between crystal nucleation and liquid water.
In ultrapure water, what is difficult and does not readily take place? What can occur?
Nucleation
SUPERCOOLING
What is supercooling?
When the water stays liquid well below 0 degrees C
Supercooled water will freeze almost instantly if _______ or if an ________ is thrown in.
- Disturbed
2. Ice crystal
In normal water, what aids the start of nucleation?
Impurities such as dust or container wall surface
The nucleation process is a function of _________.
the rate of cooling
What is the result of a slow freezing rate of water? A rapid freezing rate?
A few large ice crystals
Many small ice crystals
How does slow freezing affect meat?
Larger ice crystals form, which can become large enough to burst the cell walls, causing physical damage that reduces water holding capacity and activates enzymes previously contained
How does rapid freezing affect meat?
Small ice crystals form uniformly through the product
Solutes interfere with the ________ process and also _________ the rate of diffusion of water to the ice crysta
nucleation
slow down
What happens to the solutes as the freezing process takes place?
They become more concentrated as the water diffuses to the surface of the crystal.
As the solutes become more concentrated, a _______ temperature is required for the ice to form.
lower
What is the eutectic point? What temperature range does it occur at?
When the temperature is low enough that the solution can become concentrated to a point at which the remaining water co-crystallizes with the solute crystals to start to grow and form.
-55C to -70C
When the eutectic point has been reached, what happens to all the water in the system?
immobilized
What are the conventional frozen storage tempuratures?
0F or -18C
Is total stability attained in a frozen food product?
No, only ~98% is immobilized
What becomes disrupted in cells when large ice crystal form?
Organelles
What concentrates in cells when large ice crystal form? Why does this concentrated solution not freeze totally?
Salts, ions, enzymes, and other solutes.
Because the temperature is well below the eutectic point.
What is interesting about water when large ice crystals form in cells and salts, ions and enzymes all concentrate?
Water is still available to act as a REACTANT and the REACTION MEDIUM is very concentrated.
Can reactions still take place when large ice crystals form in cells?
Yes, all types of reactions can still take place. Enzyme and substrates that are usually kept apart are mixed due to tissue disruption.
What can denature proteins in cells that have formed large ice crystals? Net result?
Ionic strength and pH changes . Deterioration
Do frozen foods have an infinite shelf life?
No b/c of large crystal formation which leads to a high solute in water concentration where many reactions can take place which ultimatly leads to deterioration
Because enzymatic reactions carry on under conditions of frozen storage, fruits and vegetables have to be ______ before being frozen.
blanched
What is blanching/
mild heat treatment
All reactions speed up when the _______ process is started.
thawing
During what step is a lot of a food’s quality lost relative to frozen storage?
Thawing
In what two ways can water be present in foods?
Bound or free
Free water vs bound water
Free: relatively mobile
Bound: effectively immobile
One way of assessing the mobility of water is to measure its ________.
Water activity
What is the formula for water activity? (Aw) ...where... P= P0= T=
Aw = P/(P0 x T)
P= partial pressure of the solution (or food matrix)...or...the vapor pressure above the solution. P0= partial pressure of pure water T= temp
What is the scale used to measure water activity?
0 to 1.0
What is the water activity of pure water?
1.0
A sealed container containing water comes to an equilibrium between what at any constant temperature?
Liquid water and its vapor form
What would happen if we measured the partial pressure of water vapor in the headspace over water?
We would obtain some constant value at a constant temp
Would the partial pressure (or RH) of a 25% NaCl solution be greater or higher than the partial pressure of a solely water solution? Why?
It would be reduced significantly because the salt, by being solvated, ties up some of the water, restricting its freedom of movement (activity) or mobility
The ratio of the partial pressures is a useful measure of the relative _____, _____, or _____of water.
mobility, activity, availablility
Any solute will _____ the activity of water.
Reduce
We can classify the water in foods based on their _____________.
Water activity ranges
What is Type IV water?
Pure water
Aw = 1.0
Does pure water exist in food systems?
No
What is the water activity of Type III water?
Aw = 0.99 - 0.80
Where can Type III water be found in animals/meat? Present in what? Diameter?
Trapped in the tissue matrix. (the water present in macrocapillaries > 1um in diameter)
How many solutes does Type III water contain?
Contains some solutes but not enough to immobilize the water in any major way.
In Type 3 Water activity range, many _________ are capable of growth, with some ________ and _______ inhibited at the lower end of the range
Microorganisms
Bacteria & yeasts
What 3 type or reactions proceed readily in Type III water activity range?
Hydrolytic, oxidative, enzymatic
Is the freezing point much lower in Type III water than in normal water?
no its not really that much lower
What is the water activity of type II water?
Aw = 0.80 - 0.25
What is the broad range of Type II Water?
From water in microcapillaries (<1 um in diameter) to outer layers of “bound water” (water hydrogen-bounded to solutes)
What is the microbial growth in Type II Water? What about molds?
Most microbial growth is halted, with the exception of some molds at the upper end of this range.
What is the freezing point of Type II Water relative to normal water?
significantly reduced
What happens to most enzymatic reactions requiring water in Type II Water?
Slowed significantly
Discuss non-enzymatic browning at both ends of the Type II Water range.
Non-enzymatic browning takes place readily with heat at the upper end of this range – it also occurs without heat but over time at the lower end of this range.
What is the water activity of Type 1 Water?
Aw = 0.25 - 0
What is Type 1 Water?
Bound monolayer of water directly hydrogen-bonded to molecules (proteins/COHs).
Type I Water is very strongly hydrogen-bonded to the molecules and an ______ part of the molecular structure - essentially _______.
integral
immobile
Type 1 water can not be what?
Frozen
What type of reactions can take place in type 1 water?
Autoxidation
________ occurs when a “wet” food is placed in a dry environment.
Desorption
What does desorption imply?
That the food is moving toward equilibrium with the environment
What is dehydration?
The permanent loss of water from a food
What happens to the Aw in both desorption and dehydration?
Decreases
Does desorption happen slowly or rapidly?
Slowly, with moisture gradually decreasing until the food is in equilibrium with its environment
_______ occurs when a “dry” food is placed in a wet environment
Absorption
What happens as foods gain moisture?
Aw increases
What is the term “hygroscopic” used to describe?
Foods or chemicals that absorb moisture
How do hygroscopic foods pose a problem in the food industry?
Lumping, clumping, increased rxn rates
What does water activity tell a food scientist?
Potential stability
Loss/gain of moisture as a function of relative humidity
How man food scientists determine the water activity profile of a food product?
By deriving a moisture sorption isotherm
How is a moisture sorption isotherm derived? What happens once the samples have come to an equilibrium?
Dry the food product completely, then place it in an enclosed HERMETICALLY SEALED chamber above a saturated salt solution of known ERH at a constant tempurature. The salt solution contains a wide variety of salts which generate a specific Aw.
They are weighed to determine the amount of moisture adsorbed (g H2O/g dry weight) = the equilibrium moisture content (EMC)
What is Aw directly related to which is much easier to measure?
Equilibrium relative humidity (ERH)
Aw = P/P0(T) = ERH at a constant tempurature
A plot of what provides the moisture sorption isotherm? What does this plot illustrate?
Equilibrium moisture content EMC vs. Aw
Illustrates how the food product would behave as a function of relative humidity in terms of water absorption or loss at a given temperature
Moisture sorption plots are ________ dependent.
Temperature
What is a phenomenon that commonly occurs in Plots of water content vs water activity?
Directional hysteresis
What is directional hysteresis?
When a curve on a water content vs activity plot is different depending on whether the product started out dry or moist. So the same product could have a different curve depending on its initial Aw
What can permanently change the moisture sorption behavior of steak?
Drying it, which causes irreversible chemical and physical reactions to take place
Except in very simple systems, the moisture sorption curves will show _________.
hysteresis
What does moisture sorption information define?
How a product picks up or loses moisture under specific conditions (relative humidity)
What can moisture sorption data be helpful for determining?
the final moisture content that can be obtained in a drying operation based on temperature and relative humidity (RH) of the drying air
Moisture sorption data provides important information about the relative stability of a product in regards to what two factors?
- the type of microbial growth possible
2. The type of reactions that may predominate in a food system
What 5 factors are of major concern with reguards to water activity?
- Enzymatic reactions
- Lipid oxidation
- Hydrolytic reactions
- Non-enzymatic browning
- Various forms of microbial growth
What does the fact that most reactions are exponential functions of water activity imply?
That even en a slight reduction of water activity will have a significant effect in reducing the rate of a reaction
A break point for many reactions lie around Aw = ?
0.80
Aw has to be reduced down to what value 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
What is the optimum Aw?
0.3-0.4
What are 3 ways to control water activity?
- Remove water (dehydration or concentration)
- Convert the free water to bound water
- Freeze the food
How does the removal of water affect the physical nature of the food?
Alter its color, texture, and/or flavor
How can free water be converted to bound water?
Addition of sugars, salts (water soluble agents)
What does freezing food to to the water?
Immobilizes it and lowers the Aw
What is the hurdle concept?
Control Aw, pH, ionic strength, modification of atmosphere as “hurdles” the pathogen has to overcome if it is to remain active in the food
What two general categories can food systems be divided into?
- Intact edible tissues
2. Food dispersions
What are intact edible tissues?
Natural biological systems - plant and animal tissues - very complex
What are food dispersions?
Complex systems - man made
What is a dispersion?
A system consisting of one or more discontinuous phases (dispersed) in a continuous phase
What is an example of a colloidal system?
Addition of acid to whey protein
What 3 general classes can we classify solutions into?
- True solutions (or molecular dispersions)
- Colloidal dispersions
- Suspensions
What are the 5 characteristics of true solutions?
- The molecules and ions are present in their lowest subdivision.
- The particles are <0.1 μm in diameter.
- The solution formed is transparent.
- The solution has high osmotic pressure
- The solution passes through parchment membranes
What allows a solution to be considered collodial?
If it does not pass through a parchment membrane but does not settle under the force of gravity
A colloidal material is usually which of 2 things?
- macromolecule
2. an aggregate of a smaller molecule
What is the size range of colloidal dispersions?
0.1-1 micrometers
Colloidal solutions have significantly reduced ____________.
osmotic pressure
What is the color of colloidal solutions?
May be transparent but is often translucent - scatters light
What do true colloids not do? What might they do?
They do not settle out of solution and may aggregate to form gets
What are the particle sizes in suspensions?
> 1 micrometer
What color are suspensions?
Opaque
Can the suspended material be filtered out in suspensions?
Yes
How do suspensions settle out of solutions?
By gravity with time
How much osmotic pressure do suspensions show?
negligible / no measurable osmotic pressure
What happens to ungelatinized starch solutions when stirred?
Form suspensions but then soon settle out
What do gelatinized starchs form?
Colloidal solitions
or
Gel (depends on [])
What are true solutions considered to be?
uniphasic
What are colloidal solutions considered to be?
biphasic
What are suspensions considered to be?
biphasic
The conversion of a true molecular solution to a colloidal solution often takes place when _______ are involved.
macromolecules
What does charge repulsion depend on?
pH
Under what circumstances can macromolecules associate?
Via electrostatic interactions, hydrophobic interactiions, & hydrogen bonding if the overall charge repulsion is not too great
What does wastewater from food processing plants often contain?
Colloidal material
What is a common method of wastewater treatment?
Convert colloidal solutions into suspensions that will settle out by adding salts to neutralize the charge of the colloids
In food dispersions ranging from simple biphasic to multiphasic, the formation of colloids is the combined result of what 4 reactions?
- Electrostatic interactions
- H-bonding
- Hydrophobic interactions
- Hydrophobic/hydrophilic associations
Which reaction which results in the formation of colloidal solutions is the basis of many food dispersions?
Hydrophobic/hydrophilic associations
What are the 4 types of common food dispersions?
- Liquid in liquid - emulsion
- Gas in liquid - foam
- liquid in solid - solid emulsion
- Gas in liquid - solid foam
________ and ________ involve the dispersion of a hydrophobic material in a hydrophilic material and vice versa.
Emulsions, foams
Are foams and emulsions favorable or unfavorable from a free energy standpoint?
unfavorable
What is a surface-active agent? AKA?
Any compound that has both hydrophilic and hydrophobic groups in its molecular structure. More commonly termed surfactant.
Surfactants have the property to do what? What does this cause? What can be formed?
Reduce the surface tension of water significantly. This causes foaming and can form emulsions
Surfactant is a term used in what application? Example?
Non-food applications
Ex: soap is a good surfactant and foams readily
Where is the location of the lowest free energy state for emulsifiers and surfactants?
the air-water interface which is why they start off there
Molecularly, why are hydrophobic compounds attracted to the air-water interface when added to a hydrophilic medium?
The hydrophobic ends of the molecule orient themselves toward hydrophobic air, and the hydrophilic ends of the molecule orient themselves into the water
What is the net effect of the air-water interface formed when a hydrophobic material is placed in a hydrophilic medium?
Reduction of the surface tension of the water
Emulsifiers and surfactants not only reduce the _________ of water but are capable of forming structures called _______ in solution
- surface tenstion
2. micelles
What are micelles?
Colloid-like particles which are produced by hydrophobic-hydrophilic head-to-tail association
When are micelles formed in solutions?
When the concentration of an emulsifier or surfactant added to a solution is increased beyond the surface-covering capacity
Micelles form so as to reduce the ________ of the solution after the air/water interface has been ________.
Free energy
Saturated
Micelles serve as a reservoir of what?
Surfactant molecules capable of migrating to the new surfaces that are created by mixing
What does the hump in a Surface Tension vs. Concentration (or surfactant) plot mean?
Micelle formation
How much does the surface tension of a solution increase if you keep adding surfactants after the micelles have already formed?
Barely
What types of molecules are amphipathic and act as emulsifiers?
Phospholipids and monoglycerides
What are the 3 reasons to make emulsions?
- To incorporate oil into a food system without imparting an oily sensation
- To develop a unique texture, enhance the viscosity of the system or obtain plastic properties
- To change the optical characteristic of a product
The opacity of an emulsion is a function of _______________________, which is a function of _____________________.
- the droplet size of the dispersed phase
- the energy put into the system
What is the droplet size of emulsions in which you can distinguish the phases?
Macrogobules (>1 micrometer)
What is the droplet size of emulsions that appear milky white?
~ 1 micrometer
What is the droplet size of emulsions that appear bluish white?
1 micrometer - 0.1 micrometer
What is the droplet size of emulsions that appear gray-semitransparent
0.1 micrometer - 0.05 micrometers
What is the droplet size of emulsions that appear clear?
< or = to 0.05 micrometers
What are the two basic categories of emulsifiers?
Non-ionic, ionic
Which category of emulsifiers is the most important and widely used group? Why?
Non-ionic because they are insensitive to pH
What are non-ionic emulsifiers?
Emulsifiers based on glycerol esters (mono- and diglycerides) and their non-charged derivatives
What is the estimated consumption of monoglycerides in pounds/annum?
~250 million pounds/annum
Nowadays, pure monoglycerides/diglycerides are manufactured by __________ followed by ____________ to obtain relatively pure fractions.
Interesterification
Fractional distillation
What is the plasticity of monoglycerides controlled by?
overall IV
What is the IV of dry powdered monoglycerides?
19-36
What is the IV of plastic emulsifiers?
65-67
How are acetylated monoglycerides formed?
By reacting the monoglyceride with acetic acid?
How are polyoxyethylene monoglycerides produced? What does this lead to?
By treating monoglycerides with ethylene oxide - leads to polymerization of ethylene oxide as well as the connection of the polymer to the hydroxyl group at either the 2- or 3-position on the glycerol backbone
How long is a polyexyethylene chain?
~20 ethylene units
What is the main application of polyexylethylene monoglycerides in food chemistry?
cake production for emulsification & air incorporation
What are 2 other derivatives of non-ionic emulsifiers?
- lactylated monoglycerides
2. propylene glycol esters
What are sorbitan derivatives?
Sugar alcohols esterified to FA
How is sorbitan monostearate produced?
by reacting sugar alcohol with stearic acid in the presence of a catalyst
How can sorbitan derivatives be further modified?
by reacting with ethylene oxide to form polyoxyethylene derivatives
What are esters of polyhydric compounds?
Polyglycerol derivatives and sugar esters
How is polyglycerol formed? What is the average degree of polymerization normally controlled to be?
polymerization of glycerol by reacting glycerol with an alkaline catalyst, then esterified with a FA
n=2 to n=10(decaglycerol)
What is an example of a sugar ester?
Olestra
What is olestra?
A non-caloric fat substitute. Sucrose esterified with 6-8 FAs
What are the 3 types of ionic emulsifiers?
- Anionia (-)
- Amphoteric (+/-)
- Cationic (+)
What are anionic (-) emulsifiers?
charged monoglyceride derivatives
What is the most important anionic monoglyceride? How is it produced?
succinylated monoglyceride (SMG)
Produced by reacting monoglyceride with succinic anhydride
What is an example of a non-glycerol-based anionic emulsifier?
stearoyl-2-lactylate
stearoyl-2-lactylate form very stable ___________ emulsions which are resistant to ____________ and is therefore good for ________.
oil-in-water
freeze/thaw cycles
frozen foods
What type of emulsifier is sodium lauryl sulfate? What is its main use? How are they created?
Anionic
Whipping aid for egg white
Produced by the reduction of coconut oil fatty acids (~C12) to their alcohols followed by sulfonation of the alcohols produced
Why are cationic (+) emulsifiers not used as food additives?
Because they are bacterial/toxic
What are cationic (+) emulsifiers extensively used as? Why?
Cleaning compounds - they lift and emulsify food residues - very strong surface-active agents
What is your typical example of cationic (+) emulsifiers? Such as?
Quatrenary ammonium compouds –> cetyltrimethylammonium bromide
What is an example of an amphoteric (+/-) emulsifier? This compound is commonly produced as a by-product from what?
lecithin (phospholipid) - byproduct from soybean, corn, safflower oil processing
What is the majority of lecithin made up of? What may it contain?
Phosphatidylcholine and phosphatidylethanolamine
May contain phosphatidylinositol
Lechithin is usually treated with __________ and/or __________ to bleach the product.
hydrogen peroxide
benzoyl peroxide
What does bleaching of lecithin produce?
hydroxyl groups at the sites of FA unsaturatoin
What is beneficial about hydroxylated lecithin?
- More dispersible in cold water
- a more effective emulsifier than lecithin
Proteins fall under the heading of being ________ emulsifiers, but whether they function as such depends on their ________and __________.
Ionic
Structure and AA composition
What is the role played by proteins in sausage emulsions?
Form a protein film around the oil droplets, preventing coalescence of the fat
Proteins often partially ____________ at the phase interface and orient themselves in relation to the respective phases.
denature
What is an example of a type of protein that has good foam-forming properties?
egg albumin
Ionic emulsifiers have the ________ of being relatively sensitive to _____ and the presence of _______.
Disadvantage
pH
other ions
What group of compounds are often used in conjunction with emulsifiers?
Hydrocolloids
What type of compound are hydrocolloids? such as?
polysaccharides - starch and gums
Hydrocolloids are not considered true _________ but are termed ________ _______.
emulsifiers
stabilizing agents
What is the major contribution of hydrocolloids?
They increase the viscosity of the hydrophilic phase (usually the continuous phase) which makes it more difficult for the oil droplets to coalesce
What one stabilizing mechanism of hydrocolloids?
Formation of a light gel which traps the oil droplets
What can gums form around oil emulsion droplets? Which 2 gums do this?
Film
Gum arabic and gum ghatti
How are emulsifiers assessed?
HLB (hydrophilic-lipophilic balance)
What do HLB systems do? What type of emulsifiers is this system mainly applicable to?
They help people select emulsifiers. Mainly applicable to non-ionic emulsifiers
What does the HLB value represent? Example:
The weight percentage of hydrophilic groups in a non-ionic emulsifier molecule divided by 5
Ex: if 50% of the molecular weight of a molecule is hydrophilic HLB=50/5=10
What is the HLB of a molecule that is completely lipophilic?
HLB = 0
What is the HLB of a molecule that is completely hydrophilic?
HLB=100/5=20
What is the HLB of glycerol monooleate emulsifiers?
2.8
What is the HLB of lechitin emulsifiers?
4.2
What is the HLB of polyoxyehylene sorbitan strearate emulsifiers?
10.5
What is the HLB of polyoxyehylene strearate emulsifiers?
16.9
What HLB range do hydrophobic molecules fall under? What type of emulsions do they promote?
1-6
water-in-oil (w/o)
What HLB range do hydrophilic molecules fall under? What type of emulsions do they promote?
12-20
oil-in-water (o/w)
What HLB range do intermediate molecules fall under? What type of emulsions do they promote?
7-11
either w/o or o/w
The HLB system provides ______ in selecting and blending emulsifiers to obtain a specific HLB.
guidance
HLB systems can include assessment under what kind of conditions? Such as?
stress
freezing, high temp, agitation
What is the HBL range for water in oil emulsifiers?
4-6
What is the HBL range for wetting agents?
7-9
What is the HBL range for oil-in-water emulsifiers?
8-18
What is the HBL range for detergents?
13-15
What is the HBL range for solubilizers?
15-18
In what 3 ways are emulsifiers used as conditioners?
Bread doughs
Dehydrated potatoes
Processed cereals
Emulsifiers as conditioners increase ________ and have the ability to improve the _____ and ________ strength of proteins such as ________.
- water absorption
- cohesive
- film foaming
- gluten
Emulsifiers that are used as conditioners improve what? And allow more use of wat type of protein?
- tolerance to mixing
2. non-wheat
The uses of emulsifiers as conditioners results in improved _______ _______ and ____ _______ and greater resistance to ________.
- loaf volume
- crumb texture
- resistance to staling
What are 4 ways that emulsifiers can be used as wetting agents?
- Gelatin dessert mixes
- dry beverage mixes
- Cocoa powder
- pudding mixes
What are 3 benefits of the use of emulsifiers as wetting agents?
- Provide better hydration characteristics
- Increase rate of dispersion
- Minimize clumping
What is the primary role of emulsifiers? Why is this important?
Formation and stabilization of complex dispersions. Important in terms of obtaining desired sensory and textural characteristics of a food product
Why do we need a wide range of emulsifiers?
to maintain product characteristics for long periods of time & under stress conditions (thermal processing, freezing, baking, freeze/thaw stresses)
