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Food Chemistry 1 > Food dispersions > Flashcards

Food dispersions Flashcards

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1
Q

food systems can be divided into 2 general categories:

A
  1. intact edible tissues: natural biological systems like plant and animal tissues (ie. fruit, veggie, meat)
  2. food dispersions: complex systems that are usually man-made
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2
Q

what is a dispersion?

A

system consisting of one or more discontinous phases (dispersed) in a continuous phase

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3
Q

3 general classes of solutions/dispersions?

A
  1. true solutions/molecular dispersions
  2. colloidal dispersions
  3. suspensions
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4
Q

5 characteristics of true solutions?
- diameter? color? osmotic pressure? passes through what?

A
  1. molecules and ions are present in their lowest subdivision (ie simple salt or sugar)
  2. particles are < 0.1 um in diameter
  3. transparent (no light scattering)
  4. high osmotic pressure
  5. passes through parchment membrane
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5
Q

characteristics of colloidal dispersions
- 2 conditions?
- usually a ___________ or an ___________ of a smaller molecule –> may ___________ to form ___________
- size range?
- osmotic pressure?
- color?

A
  1. do NOT pass through parchment membranes
  2. 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
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6
Q

characteristics of suspensions
- particle size?
- color?
- suspended material? filtered out? gravity?
- osmotic pressure?
- ex of ungelatinized starch granules vs gelatinized

A
  • > 1um
  • generally opaque
  • suspended material can be filtered out –> settle out of solution by gravity, given enough time
  • no measurable osmotic pressure
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7
Q

what types of solutions do ungelatinized starch granules vs gelatinized sarch form?

A
  • ungelatinized starch granules will form a suspension when stirred but soon settle out
  • gelatinized starch forms a colloidal solution or gel depending on concentration
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8
Q

true solution vs colloidal solutions:
- which is uniphasic/biphasic?

A
  • true solution: uniphasic (you don’t see 2 phases)
  • colloidal: biphasic
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9
Q

conversion of true molecular solution to a colloidal solution often takes place when ____________ are involved

A

macromolecules

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10
Q

if overall charge is low –> macromolecules will ____________ –> how?
VS if overall charge accumulating becomes large, macromolecule will ____________

A
  • low charge –> aggregate –> electrostatic interactions, hydrophobic interactions, hydrogen bonding
  • large charge –> repulse each other (think about caseins)
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11
Q

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?

A
  • colloidal material
  • colloidal solutions into suspensions
  • by adding salts to neutralize the charge of the colloids
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12
Q

in food dispersions, formation of colloids is the combined result of (4) what interactions?

A
  1. electrostatic interactions
  2. hydrogen bonding
  3. hydrophobic interactions
  4. hydrophobic/hydrophilic associations
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13
Q

4 common food dispersions (ie what in what)?

A
  1. liquid in liquid = emulsion
  2. gas in liquid = foam
  3. liquid in solid = solid emulsion (butter)
  4. gas in solid = solid foam (whipping cream)
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14
Q

food dispersions are favorable/unfavorable from a free energy standpoint –> explain?

A
  • unfavorable
  • high interfacial tension/surface tension can be reduced by emulsifiers or surfactants via hydrophobic/hydrophilic associations
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15
Q

what is a surfactant?
- have property of what?

A
  • 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
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16
Q

emulsifier vs surfactant?

A

both are the same thing!
- but emulsifier = food products
- surfactants = non-food applications (like soap)

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17
Q

what happens when surfactants are mixed into a solution?
- 2 steps

A
  1. 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!
  2. 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
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18
Q

does surface tension increase or decrease when surfactants are added?
- what happens to surface tension when too much surfactant is added?

A
  • decrease!
  • too much –> surface tension doesn’t change substantially bc micelles are formed
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19
Q

emulsifiers have both ____________ and ____________ groups = ____________ nature
- 2 ex. of emulsifiers?

A
  • hydrophobic and hydrophilic
  • amphipathic
    ex.: phospholipids and monoglycerides
20
Q

3 reasons to make emulsions

A
  1. to incorporate oil into a food system without imparting an oily sensation
  2. to develop a unique texture, enhance viscosity of system or obtain plastic properties
  3. to change optical characteristics of a product (ie white mayo)
21
Q

opacity of an emulsion is a function of droplet ____________ of the ____________ phase, which is a function of the ____________ put into the system

A
  • droplet size of the dispersed phase
  • function of energy put into system
22
Q

2 basic categories of emulsifiers?
- which one is most used?

A
  1. non-ionic –> most important and widely used group bc they are insensitive to pH
  2. ionic
23
Q

non ionic emulsifiers:
- based on ___________ esters (2 ex) and their non-___________ derivatives
- use began in 1930s for what? –> forming what

A
  • 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
24
Q

nowadays, how are mono/diglycerides manufactured? (2 steps ish)

A
  • through interesterification followed by tractional distillation to obtain relatively pure fractions
25
Q

FA composition of monoglyceride affects its ___________ and its plasticity is controlled by its overall ___________ ___________
- explain

A
  • 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)
26
Q

____________ of sugars is also possible to produce emulsifiers
- ex?

A

esterification (adding alkyl groups on each OH)
- Olestra = non-caloric fat substitute (but too much is bad –> vomit)

27
Q

3 subcategories of ionic emulsifiers?

A
  1. anionic (negative)
  2. amphoteric (+/-)
  3. cationic (+)
28
Q

anionic emulsifiers are ___________ ____________ derivatives
- most important one is ____________ ____________, produced by reaction of ____________ with ____________ ____________
- non-glycerol- based anionic emulsifiers also exist like what?

A
  • charged monoglyceride derivatives
  • succinylated monoglyceride (SMG)
  • reaction of monoglyceride with succinic anhydride
  • sodium stearoyl-2-lactylate
29
Q

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

A

oil-in-water emulsions
- freeze/thaw cycles
- frozen foods

30
Q

which anionic emulsifier is used as a whipping aid for egg white?
- how is it produced?

A
  • sodium lauryl sulfate
  • produced by reduction of coconut oil FA (C12) to their alcohols followed by sulfonation of alcohols produced
31
Q

are cationic emulsifiers used as food additives?
- explain
- ex?

A
  • 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
32
Q

example of amphoteric emulsifier?
- commonly produced as by-product from (3) oil processing
- usually a complex mixture of (3) phospholipids

A
  • lecithin! (phospholipid)
  • soybean, corn, safflower oil processing
  • may contain come phosphatidylionsitol (anionic) but the bulk is phosphatidulcholine (amphoteric) and phosphatidylethanolamine (amphoteric)
33
Q

lecithin is usually treated with hydrogen peroxide and/or benzoyl peroxide to _____A_____ the product
- what does _____A_____ produce?

A
  • 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
34
Q

are proteins ionic emulsifiers?
- explain

A
  • 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)
35
Q

what are hydrocolloids?
- generally what?
- __________ agents
- major contribution lies in what?

A
  • 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
36
Q

gums can also form __________ around oil emulsion droplets –> role played by 2 types of gums

A
  • films
  • gum arabic
  • gum ghatti
37
Q

which system to assess emulsifiers?
- how?
- mainly applicable to what?
- value represents what?

A

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

38
Q
  • completely lipophilic system: HLB = ?
  • completely hydrophilic: HLB = ?
A
  • lipophilic: HLB = 0
  • hydrophilic: HLB = 100/5 = 20
39
Q
  • glycerol monooleate
  • polyoxyehylene sorbitan stearate
  • lecithin
  • polyoxyethylene stearate
    HLB of?
    2.8
    4.2
    10.5
    16.9
A
  • glycerol monooleate: 2.8
  • polyoxyehylene sorbitan stearate: 10.5
  • lecithin: 4.2
  • polyoxyethylene stearate: 16.9
40
Q
  • hydrophilic or phobic?
  • promote which type of emulsion?
    1. HLB between 1 and 6
    2. HLB: 7-11
    3. HLB: 12-20
A
  1. HLB 1-6 –> hydrophobic –> water-in-oil emulsions
  2. HLB: 7-11 –> intermediate –> either w/o or o/w emulsions
  3. HLB: 12-20 –> hydrophilic: oil-in-water emulsions
41
Q

capabilities of emulsifiers to produce o/w or w/o emulsions is also a function of the ___________ ratio

A

oil/water ratio

42
Q

what is done to give a more stable emulsion as they tend to have a ___________ effect?

A
  • 2 or more emulsifiers are blended
  • synergistic effect
43
Q

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?

A
  • guidance!
  • %B = 100 (target HLB - HLB(A)) / (HLB(B) - HLB (A)
  • %A = 100 - %B
44
Q

use of emulsifiers as conditioners in 3 food products?
- what does it do? (3)

A
  • 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
45
Q

use of emulsifiers as wetting agents in 4 food products?
- 3 roles?

A
  • gelatin dessert mixes, dry beverage mixes, cocoa powder, pudding mixes
  • provide better hydration characteristics
  • increase rate of dispersion
  • minimize clumping
46
Q
  1. primary role of emulsifiers?
  2. need a wide range of emulsifiers for what?
A
  1. primary role = formation and stabilization of complex dispersions –> important to obtain desired sensory and textural characteristics of a good product
  2. because of need to maintain product characteristics for long periods of time + under stress conditions (thermal processing, freezing, baking, freeze/thaw stresses)

Food Chemistry 1 (22 decks)

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