Food dispersions Flashcards
food systems can be divided into 2 general categories:
- intact edible tissues: natural biological systems like plant and animal tissues (ie. fruit, veggie, meat)
- food dispersions: complex systems that are usually man-made
what is a dispersion?
system consisting of one or more discontinous phases (dispersed) in a continuous phase
3 general classes of solutions/dispersions?
- true solutions/molecular dispersions
- colloidal dispersions
- suspensions
5 characteristics of true solutions?
- diameter? color? osmotic pressure? passes through what?
- molecules and ions are present in their lowest subdivision (ie simple salt or sugar)
- particles are < 0.1 um in diameter
- transparent (no light scattering)
- high osmotic pressure
- passes through parchment membrane
characteristics of colloidal dispersions
- 2 conditions?
- usually a ___________ or an ___________ of a smaller molecule –> may ___________ to form ___________
- size range?
- osmotic pressure?
- color?
- do NOT pass through parchment membranes
- does NOT settle under force of gravity (stays in solution)
- a macromolecule or an aggregate of a smaller molecule –> may aggregate to form gels
- 0.1-1 um
- significantly reduced osmotic pressure
- may be transparent but is often translucent –> scatters light
characteristics of suspensions
- particle size?
- color?
- suspended material? filtered out? gravity?
- osmotic pressure?
- ex of ungelatinized starch granules vs gelatinized
- > 1um
- generally opaque
- suspended material can be filtered out –> settle out of solution by gravity, given enough time
- no measurable osmotic pressure
what types of solutions do ungelatinized starch granules vs gelatinized sarch form?
- ungelatinized starch granules will form a suspension when stirred but soon settle out
- gelatinized starch forms a colloidal solution or gel depending on concentration
true solution vs colloidal solutions:
- which is uniphasic/biphasic?
- true solution: uniphasic (you don’t see 2 phases)
- colloidal: biphasic
conversion of true molecular solution to a colloidal solution often takes place when ____________ are involved
macromolecules
if overall charge is low –> macromolecules will ____________ –> how?
VS if overall charge accumulating becomes large, macromolecule will ____________
- low charge –> aggregate –> electrostatic interactions, hydrophobic interactions, hydrogen bonding
- large charge –> repulse each other (think about caseins)
wastewater from food processing plants often contains substantial amounts of ____________ material –> a common method of wastewater treatment is to convert these ____________ solutions into ____________ that will settle out by adding what to do what?
- colloidal material
- colloidal solutions into suspensions
- by adding salts to neutralize the charge of the colloids
in food dispersions, formation of colloids is the combined result of (4) what interactions?
- electrostatic interactions
- hydrogen bonding
- hydrophobic interactions
- hydrophobic/hydrophilic associations
4 common food dispersions (ie what in what)?
- liquid in liquid = emulsion
- gas in liquid = foam
- liquid in solid = solid emulsion (butter)
- gas in solid = solid foam (whipping cream)
food dispersions are favorable/unfavorable from a free energy standpoint –> explain?
- unfavorable
- high interfacial tension/surface tension can be reduced by emulsifiers or surfactants via hydrophobic/hydrophilic associations
what is a surfactant?
- have property of what?
- any compound that has both hydrophilic and hydrophobic groups in its molecular structure
- reducing surface tension of water significantly, causing foaming, and can form emulsions
emulsifier vs surfactant?
both are the same thing!
- but emulsifier = food products
- surfactants = non-food applications (like soap)
what happens when surfactants are mixed into a solution?
- 2 steps
- surfactants are found near solution surface –> air-water interface = location of lowest free energy state for emulsifiers and surface-active compounds –> hydrophobic ends orient toward hydrophobic air + hydrophilic ends orient themselves into water
- this orientation forms transitional region which reduces free energy differential btw hydrophilic water and hydrophobic air
- reduces surface tension of water! - if concentration of emulsifier/surfactant is increased beyond surface-covering capacity, then micelles are formed in solution –> formed to reduce the free energy of the solution after the air/water interface is saturated
- micelles serve as reservoir of surfactant molecules capable of migrating to new surfaces that are created by mixing
does surface tension increase or decrease when surfactants are added?
- what happens to surface tension when too much surfactant is added?
- decrease!
- too much –> surface tension doesn’t change substantially bc micelles are formed
emulsifiers have both ____________ and ____________ groups = ____________ nature
- 2 ex. of emulsifiers?
- hydrophobic and hydrophilic
- amphipathic
ex.: phospholipids and monoglycerides
3 reasons to make emulsions
- to incorporate oil into a food system without imparting an oily sensation
- to develop a unique texture, enhance viscosity of system or obtain plastic properties
- to change optical characteristics of a product (ie white mayo)
opacity of an emulsion is a function of droplet ____________ of the ____________ phase, which is a function of the ____________ put into the system
- droplet size of the dispersed phase
- function of energy put into system
2 basic categories of emulsifiers?
- which one is most used?
- non-ionic –> most important and widely used group bc they are insensitive to pH
- ionic
non ionic emulsifiers:
- based on ___________ esters (2 ex) and their non-___________ derivatives
- use began in 1930s for what? –> forming what
- glycerol esters (mono and diglycerides) and their non-charged derivatives
- use began when glycerol was added to fats with small amount of base to interesterify the fat to produce some monoglycerides –> product was termed superglycerinated shortening containing 3% monoglyceride –> greatly enhances cake volume, especially at high sugar levels
nowadays, how are mono/diglycerides manufactured? (2 steps ish)
- through interesterification followed by tractional distillation to obtain relatively pure fractions
FA composition of monoglyceride affects its ___________ and its plasticity is controlled by its overall ___________ ___________
- explain
- its properties
- overall iodine value
- low iodine value = less double bonds = more solid (ie dry powdered monglycerides with IVs of 19-36)
- high iodine value = more double bonds = more liquid (ie plastic emulsifiers with IVs of 65-67)
____________ of sugars is also possible to produce emulsifiers
- ex?
esterification (adding alkyl groups on each OH)
- Olestra = non-caloric fat substitute (but too much is bad –> vomit)
3 subcategories of ionic emulsifiers?
- anionic (negative)
- amphoteric (+/-)
- cationic (+)
anionic emulsifiers are ___________ ____________ derivatives
- most important one is ____________ ____________, produced by reaction of ____________ with ____________ ____________
- non-glycerol- based anionic emulsifiers also exist like what?
- charged monoglyceride derivatives
- succinylated monoglyceride (SMG)
- reaction of monoglyceride with succinic anhydride
- sodium stearoyl-2-lactylate
sodium stearoyl-2-lactylate forms very stable oil-in-water/water in oil ? emulsions which are very resistant to __________ cycles and is therefore good for __________ foods
oil-in-water emulsions
- freeze/thaw cycles
- frozen foods
which anionic emulsifier is used as a whipping aid for egg white?
- how is it produced?
- sodium lauryl sulfate
- produced by reduction of coconut oil FA (C12) to their alcohols followed by sulfonation of alcohols produced
are cationic emulsifiers used as food additives?
- explain
- ex?
- no! because bactericidal and toxic!
- very potent surface-active agents, used extensively as cleaning compounds –> lift and emulsify food residues
- ex: quaternary ammonium compounds: cetyltrimethylammonium bromide
example of amphoteric emulsifier?
- commonly produced as by-product from (3) oil processing
- usually a complex mixture of (3) phospholipids
- lecithin! (phospholipid)
- soybean, corn, safflower oil processing
- may contain come phosphatidylionsitol (anionic) but the bulk is phosphatidulcholine (amphoteric) and phosphatidylethanolamine (amphoteric)
lecithin is usually treated with hydrogen peroxide and/or benzoyl peroxide to _____A_____ the product
- what does _____A_____ produce?
- bleach!
- bleaching/oxidation produces hydroxyl groups at the sites of FA unsaturation –> this hydroxylated lecithin is more dispersible in cold water and it a more effective emulsifier than lecithin itself
are proteins ionic emulsifiers?
- explain
- yes but whether they function as such will depend on structure and amino acid composition
- proteins usually partially denature at the phase interface and orient themselves in relation to the respective phases
- ex.: sausage emulsions –> form a protein film around oil droplets, preventing coalescence of the fat
- proteins can also have good foam-forming properties (egg albumin)
what are hydrocolloids?
- generally what?
- __________ agents
- major contribution lies in what?
- generally polysaccharides such as starch and gums
- not considered true emulsifiers but are termed stabilizing agents
- lies in enhancement of viscosity of hydrophilic phase (usually the continuous phase) –> increased viscosity makes it more difficult for oil droplets to coalesce
gums can also form __________ around oil emulsion droplets –> role played by 2 types of gums
- films
- gum arabic
- gum ghatti
which system to assess emulsifiers?
- how?
- mainly applicable to what?
- value represents what?
hydrophilic-lipophilic balance (HLB)
- systematic approach to aid one in selecting emulsifiers –> mainly applicable to non-ionic emulsifiers
- HLB value represents weight percentage of hydrophilic groups in a non-ionic emulsifier molecule divided by 5
- completely lipophilic system: HLB = ?
- completely hydrophilic: HLB = ?
- lipophilic: HLB = 0
- hydrophilic: HLB = 100/5 = 20
- glycerol monooleate
- polyoxyehylene sorbitan stearate
- lecithin
- polyoxyethylene stearate
HLB of?
2.8
4.2
10.5
16.9
- glycerol monooleate: 2.8
- polyoxyehylene sorbitan stearate: 10.5
- lecithin: 4.2
- polyoxyethylene stearate: 16.9
- hydrophilic or phobic?
- promote which type of emulsion?
1. HLB between 1 and 6
2. HLB: 7-11
3. HLB: 12-20
- HLB 1-6 –> hydrophobic –> water-in-oil emulsions
- HLB: 7-11 –> intermediate –> either w/o or o/w emulsions
- HLB: 12-20 –> hydrophilic: oil-in-water emulsions
capabilities of emulsifiers to produce o/w or w/o emulsions is also a function of the ___________ ratio
oil/water ratio
what is done to give a more stable emulsion as they tend to have a ___________ effect?
- 2 or more emulsifiers are blended
- synergistic effect
HLB system provides ___________ in selecting and blending emulsifiers to obtain a specific HLB
- based on target HLB, how to calculate % of emulsifier A and B?
- guidance!
- %B = 100 (target HLB - HLB(A)) / (HLB(B) - HLB (A)
- %A = 100 - %B
use of emulsifiers as conditioners in 3 food products?
- what does it do? (3)
- bread doughs, dehydrated potatoes, processed cereals
- increase water absorption and have the ability to improve the cohesive and film-forming strength of proteins such as gluten
- improve tolerance to mixing and allow more use of non-wheat proteins
- result in improved loaf volume and crumb texture and greater resistance to staling
use of emulsifiers as wetting agents in 4 food products?
- 3 roles?
- gelatin dessert mixes, dry beverage mixes, cocoa powder, pudding mixes
- provide better hydration characteristics
- increase rate of dispersion
- minimize clumping
- primary role of emulsifiers?
- need a wide range of emulsifiers for what?
- primary role = formation and stabilization of complex dispersions –> important to obtain desired sensory and textural characteristics of a good product
- because of need to maintain product characteristics for long periods of time + under stress conditions (thermal processing, freezing, baking, freeze/thaw stresses)
