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Food Physical Systems > Huang Exam > Flashcards

Huang Exam Flashcards

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1
Q

Pectin

A

HM Pectin: Has a high concentration of methoxy groups and adding sugar forms a gel

LM Pectin: Has a high concentration of carboxylic groups and adding calcium forms a gel

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2
Q

Foam

A

Gaseous material dispersed through another material that is a liquid or a solid.

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3
Q

How is a stable foam formed

A

Surface Tension

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4
Q

Bread as a Foam

A

Has air bubbles that form from CO2 air bubbles that eventually evaporates and causes holes in bread that act as a foam

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5
Q

Amorphous structure

A

There is no molecular order, and physical properties can change by orders of magnitude at Tg (glass transition temperature)
Ex: extruded snacks

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6
Q

Glass transition temperature and the motions of molecules

A

When molecule is in a glassy state, it can still do rotational motions but can’t do transitional motions.

When temp increases past Tg, molecule can flow

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7
Q

Crystal structure

A

Molecules have long-range order and lower energy

Has sharp melting point peak

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8
Q

Semi-crystalline structure

A

Contains both amorphous and crystalline structures
Broad melting peak
Ex: Cellulose

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9
Q

Conformation of Starches

A

Amylose: linear starch and starch with high amylose content has higher crystallinity

Amylopectin: Branched Starch

Glycogen: Branched starch with a denser outer-region

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10
Q

Gelatinization of starch

A

Water absorbed in amorphous space -> number and size of crystalline region decreases -> amylose leaches into surrounding water

Native starch -> gelatinized starch -> retrograded starch

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11
Q

Polyphenols

A

Can act as antioxidants to work against lipid oxidation

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12
Q

How do antioxidants work against lipid oxidation

A

Stabilize free radical
Structures with more resonance are more stable (Ex: Benzene)

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13
Q

Polyphenols in Life

A

Anthocyanin in sweet potatoes has an oxygen with a + charge
If this is extracted, the purple is easy to degrade

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14
Q

What pH are polyphenols stable at

A

Acidic pH

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15
Q

Green tea to black tea

A

Under effects of fermentation (temperature and microorganisms), polyphenol changes to other Polyphenols with a higher molecular weight which is why the color changes

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16
Q

Thermodynamics

A

Temperature is related to thermodynamics
Provide energy
Ex: how much heat required for extrusion
Deals with direction in which a process occurs

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17
Q

Kinetics

A

Related to shelf life and quality of food

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18
Q

Thermodynamics and shelf life

A

Temperature determines kinetics through drying process

Storing a food at lower temperatures lowers rate if decay more efficiently

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19
Q

Phase diagram and phase transitions

A

Understand how to transition from one phase and temp to another and the math needed

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20
Q

Supercritical CO2 and subcritical butane in the food processing industry

A

Used in oil extraction as pressure is applied to these fluids and they go through crushed oil seed to extract the oil
Brings oil to chamber, releases pressure and these fluids evaporate as the oil remains
These fluids are used as solvents in place of organic solvents

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21
Q

Entropy

A

Measure of number of microstates that the molecules of a macroscopic system can adopt

Ice -> Water shows an increase in disorder

For an isolated system, total entropy is always larger or equal to zero

Change in entropy is positive during protein denaturation

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22
Q

Putting Food in Freezer regarding Entropy

A

The surroundings will be at the constant temp that the freezer is at (Ex: -20 C)

The change in entropy of water being placed in a freezer reflects heat of water to the freezer (both by phase change and cooling)

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23
Q

Equation for Change in entropy system during temperature change

A

ΔS = Cp*Ln(Tf/Ti)

Cp of water is 75.7 J/K
Cp of Ice is 35.6 J/K

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24
Q

Equation for change in entropy system during phase change

A

ΔS = (ΔH/T)
H: Enthalpy (May need to be converted to Joules)

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25
Q

How to calculate total entropy of the system

A

ΔStotal = Sum of all ΔS values

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26
Q

Equation for change in entropy surroundings during temperature change

A

Qcool = -Cp (phase)ΔTphase
In this case, the final temp will always be the temp of the surroundings (-20 C for the freezer)

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27
Q

Equation for change in entropy of the surroundings during phase change

A

Qfreeze = -H(water)freeze

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28
Q

Free Energy Equation

A

ΔG = ΔH -TΔS
if ΔG > 0, process is spontaneous
if Δ < 0, process requires energy

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29
Q

Enthalpy driven process

A

ΔH < 0
Formation of bonds drives process
Fat Crystallization at low T
Gelatin gelation at 5 C
Condensation

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30
Q

Entropy Driven process

A

ΔS > 0
Increase in disorder drives process
Sugar dissolving in tea
Evaporation

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31
Q

Electrostatic interactions

A

H-bonding and electrostatic interactions can occur with a + charged protein and - charged polysaccharide

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32
Q

Isoelectric Point (PI)

A

Point at which protein has an equal amount of positive and negative charge so the net charge is 0

Protein can behave positively or negatively charged depending on pH change

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33
Q

How to Solve for Keq

A

Keq = e^(-ΔG/RT)
R: 8.314 J/Kmol
make sure units match

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34
Q

Le Chatelier’s Principle

A

Reaction shifts in a direction that minimizes disturbance

Ex: Gly-Gly + H20 -> 2Gly
When Gly is high/increases, reaction shifts to the left

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35
Q

Carrageenan

A

Building block is sulfuric acid (SO3H)
Lambda: never form gel because very high negative charge and electrostatic repulsion which makes forming the helix more difficult

Iota: also forms strong gel with potassium chloride solution (non-reversible)

Kappa: easy to form gel because only has 1 sulfuric acid group every polysaccharide which makes it easy to form helix

36
Q

Are foods at an equilibrium?

A

No
Chemical reactions (oxidation, hydrolysis) and physical structures (emulsions, gradients) are not at equilibrium

37
Q

Polysaccharide + Proteins

A

Form complex due to electrostatic interactions between amino acids and polysaccharides

Amino groups can be protonated with + charge
Carboxylic group can be protonated with - charge

38
Q

Phase separation

A

pH adjusted to below isoelectric point
coacervates and solution turns turbid

39
Q

Coacervate in non-aqueous systems

A

Ex: Milk/egg whites added to an ethanol solution forms a precipitate with egg protein in one layer and alcohol and water in the other layer

40
Q

Coacervate in an aqueous solution

A

Water is a solvent
Protein will be salted out as concentration of salt increases

41
Q

pH trigger control release system

A

Ex: the stomach had an acidic pH, and the colon has an alkaline pH. Nutraceuticals and micronutrients are encapsulated to be released into the colon and not denatured in the stomach

42
Q

Complex Formation Between Charged Biopolymers

A

Charge is most important factor, and the maximum yield occurs during the isoelectric point

This complex can be suppressed by a high salt concentration as microns form a dense layer around the biopolymers and prevent electrostatic interactions

43
Q

Soluble Complexes

A

Opposite charges carried by 2 biopolymers not equal in number which results in net charge that allows complex solubilization by interaction with solvent materials

44
Q

Insoluble complexes Charges

A

of charges are equal and complex charge is 0

Coacervates or precipitates
Number of charges are equal, complex charge is 0
Sedimentation can occur

45
Q

Phase diagram for Beta-lactoglobulin

A

pH 7 has no turbidity because there is no interaction (both protein and polymer are negative)

pH 5 has + charged protein and is at the isoelectric point so interaction starts, and turbidity is high.

pH 2 has + charged protein and pectin with a low charge. Very little turbidity and low amount of electrostatic interactions

46
Q

Using carrageenan for encapsulation

A

Sulfonic acid in carrageenan is a strong acid (electrolyte) that fully dissociates over pH range

Complex can form below a pH of 5 as carrageenan remains stable in an acidic environment

47
Q

What is needed for a material to be extruded

A

Need to be processed above glass transition temperature but below degradation temperature

48
Q

Ethylene as a polymer

A

Polyethylene and Polypropylene
The way ethylene is processed can give different results and properties

49
Q

Free radicals and polymers

A

Free radicals can react with monomers that have double bonds to form an ongoing degradative reaction similar to lipid oxidation

50
Q

Stretching of Polymers

A

Contour length is the distance from one end of a molecule to the other end

Flexibility of a molecule depends on length
longer length = more rigid

51
Q

Swelling with a good solvent

A

Polymer fully dissolves and swells
Has specific interactions between polymer and solvents

52
Q

Theta Solvent

A

In-between swelling and compact structure

53
Q

what structure do polymers in a poor solvent form?

A

Molecule forms compact structure
Does not have interactions between polymer and solvents

54
Q

What are the four concentrations of a polymer in a solvent

A

Diluted solution
Semi-diluted solution
Concentration solution
Gel

55
Q

Physical gels

A

Are reversible
Eggs are an example of a non-reversible gel

56
Q

Plastic vs Rubber

A

Rubber is more elastic

Heating up plastic melts the plastic, and its mechanical strength drops to 0. The plastic drops from a solid state to a liquid state.

Rubber does not go to a liquid when heated because its mechanical property eventually stabilizes

57
Q

Synthesis of Polymer

A

Free radical polymerization and copolymerization

This process is similar to lipid oxidation

58
Q

Antibacterial Coatings on Polymer Surface

A

Use plasma on plastic surface to generate free radical and initiate polymerization with double bond molecule to create antimicrobial surface

59
Q

Antimicrobial monomers

A

Tertiary amino groups are + charged and rupture bacterial cells
Phospholipid on cell surface is negatively charged and + charged structure ruptures cell surface and cause leakage.
Ex: MADAM, DADMAC

60
Q

Polylactic acid

A

biodegradable and consumed by bacteria

61
Q

Ring opening Polyester

A

Polyester reaction or a Polycarbonate reaction can lead to a chain of open ring structures

62
Q

Notable Polysaccharide sources

A

Seaweed: agar, carrageenan
Plant cell wall soluble: pectin
Derived: modified starch

63
Q

Polysaccharides by structure

A

Linear: amylose, cellulose, pectin, alginates
Short-branched: guar gum, locust bean gum, xanthan gum
Branch-on-branch: amylopectin, gum Arabic, arabinoxylan

64
Q

Amylose/Amylopectin ratio

A

This ratio determines the properties of starch

More amyloses have more crystallization because amylose is a linear polysaccharide

65
Q

Polysaccharides by monomers

A

Homoglycans: starch, cellulose
Diheteroglycans: agars, alginate carrageenan, carrageenan
Triheteroglycans: xanthan, gellan, arabinoxylan

66
Q

Polysaccharides by charge

A

Neutral: amylose, amylopectin, cellulose, guar gum
Anionic: Alginates, carrageenan, gellan, gum Arabic, xanthan

Pectin has carboxyl group (weak acid)
Carrageenan has sulfonic group (strong acid)

67
Q

Starch

A

Semi-crystalline
Becomes gel during cooking
High on the Glycemic Index

68
Q

Why can starch form a gel

A

Starch has hydroxyl groups that hydrogen bond with water
Heat is required to promote interactions between starch and water
The amorphous stage interacts with the water first because they are more free compared to crystalline carbohydrates

69
Q

Looking at starch under polarized optical microscope

A

Can only see crystal structure under this microscope
Starch loses crystallinity when gelatinized and cannot be viewed under this microscope

70
Q

How to determine Mn

A

Mn: (Weight total)/(number total)

71
Q

How to determine Mw

A

W: M x n
Mw: (W1 x M1) + (W2 x M2) + (W3 x M3)/ W1 +W2 + W3

72
Q

Polydispersity

A

Mw/Mn
symbol is d
Larger bandwith on SEC graph has a larger polydispersity

73
Q

How to solve for Mw, Mn, polydispersity when given molecule in grams

A

This weight is the W value so plug value in grams into W value and solve

74
Q

Size exclusion chromatography 2 types

A

Gel Filtration Chromatography
Gel Permeation Chromatography

75
Q

How does SEC work

A

Separates based on molecule weight or size and no interaction occurs

76
Q

Ideal vs Non-Ideal Sec

A

Ideal: non interaction occurs
Non-ideal: interaction between occurs between solute and support

77
Q

SEC which molecules are eluted first

A

Large molecules

78
Q

How to determine Mw using SEC

A

Inject standard where MWs are already found
Graph time on y axis and Log M on x axis
Each elution time corresponds to a molecular weight

79
Q

How to choose packing material for SEC

A

Consider purpose of separation and size of molecules

80
Q

Relationship between elution volume and elution time

A

Elution volume = flow rate x time
Linear function with a constant flow rate

81
Q

How to use viscosity to determine Mw

A

Fill tube with solvent and suck solvent up to the top
Record time taken to travel from point A to point B

Higher viscosity, longer time to travel

82
Q

Specific viscosity

A

(Viscosity of sample - solvent viscosity)/Solvent viscosity

(T-T0)/T0

83
Q

Intrinsic viscosity

A

Specific viscosity when concentration if approaching 0

Function of Molecular Weight
Plot intrinsic viscosity as Y axis and concentration as X Axis

Can measure intrinsic viscosity for every polymer

Intrinsic viscosity = KMw^a

K and a are constants

84
Q

SEC Packing Material

A

Hydrophobic media (cross linked polystyrene)

Hydrophobic gels (polysaccharide-based packings)

85
Q

Simple Coacervate vs Complex coacervate

A

Separation that occurs through salting out.

Simple: Formed from a single polymer
Complex: Formed from multiple polymers

Food Physical Systems (4 decks)

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