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Food Physical Systems > Huang Exam > Flashcards

Huang Exam Flashcards

(85 cards)

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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
How to calculate total entropy of the system
ΔStotal = Sum of all ΔS values
26
Equation for change in entropy surroundings during temperature change
Qcool = -Cp (phase)ΔTphase In this case, the final temp will always be the temp of the surroundings (-20 C for the freezer)
27
Equation for change in entropy of the surroundings during phase change
Qfreeze = -H(water)freeze
28
Free Energy Equation
ΔG = ΔH -TΔS if ΔG > 0, process is spontaneous if Δ < 0, process requires energy
29
Enthalpy driven process
ΔH < 0 Formation of bonds drives process Fat Crystallization at low T Gelatin gelation at 5 C Condensation
30
Entropy Driven process
ΔS > 0 Increase in disorder drives process Sugar dissolving in tea Evaporation
31
Electrostatic interactions
H-bonding and electrostatic interactions can occur with a + charged protein and - charged polysaccharide
32
Isoelectric Point (PI)
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
33
How to Solve for Keq
Keq = e^(-ΔG/RT) R: 8.314 J/Kmol make sure units match
34
Le Chatelier's Principle
Reaction shifts in a direction that minimizes disturbance Ex: Gly-Gly + H20 -> 2Gly When Gly is high/increases, reaction shifts to the left
35
Carrageenan
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
Are foods at an equilibrium?
No Chemical reactions (oxidation, hydrolysis) and physical structures (emulsions, gradients) are not at equilibrium
37
Polysaccharide + Proteins
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
Phase separation
pH adjusted to below isoelectric point coacervates and solution turns turbid
39
Coacervate in non-aqueous systems
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
Coacervate in an aqueous solution
Water is a solvent Protein will be salted out as concentration of salt increases
41
pH trigger control release system
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
Complex Formation Between Charged Biopolymers
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
Soluble Complexes
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
Insoluble complexes Charges
# 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
Phase diagram for Beta-lactoglobulin
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
Using carrageenan for encapsulation
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
What is needed for a material to be extruded
Need to be processed above glass transition temperature but below degradation temperature
48
Ethylene as a polymer
Polyethylene and Polypropylene The way ethylene is processed can give different results and properties
49
Free radicals and polymers
Free radicals can react with monomers that have double bonds to form an ongoing degradative reaction similar to lipid oxidation
50
Stretching of Polymers
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
Swelling with a good solvent
Polymer fully dissolves and swells Has specific interactions between polymer and solvents
52
Theta Solvent
In-between swelling and compact structure
53
what structure do polymers in a poor solvent form?
Molecule forms compact structure Does not have interactions between polymer and solvents
54
What are the four concentrations of a polymer in a solvent
Diluted solution Semi-diluted solution Concentration solution Gel
55
Physical gels
Are reversible Eggs are an example of a non-reversible gel
56
Plastic vs Rubber
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
Synthesis of Polymer
Free radical polymerization and copolymerization This process is similar to lipid oxidation
58
Antibacterial Coatings on Polymer Surface
Use plasma on plastic surface to generate free radical and initiate polymerization with double bond molecule to create antimicrobial surface
59
Antimicrobial monomers
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
Polylactic acid
biodegradable and consumed by bacteria
61
Ring opening Polyester
Polyester reaction or a Polycarbonate reaction can lead to a chain of open ring structures
62
Notable Polysaccharide sources
Seaweed: agar, carrageenan Plant cell wall soluble: pectin Derived: modified starch
63
Polysaccharides by structure
Linear: amylose, cellulose, pectin, alginates Short-branched: guar gum, locust bean gum, xanthan gum Branch-on-branch: amylopectin, gum Arabic, arabinoxylan
64
Amylose/Amylopectin ratio
This ratio determines the properties of starch More amyloses have more crystallization because amylose is a linear polysaccharide
65
Polysaccharides by monomers
Homoglycans: starch, cellulose Diheteroglycans: agars, alginate carrageenan, carrageenan Triheteroglycans: xanthan, gellan, arabinoxylan
66
Polysaccharides by charge
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
Starch
Semi-crystalline Becomes gel during cooking High on the Glycemic Index
68
Why can starch form a gel
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
Looking at starch under polarized optical microscope
Can only see crystal structure under this microscope Starch loses crystallinity when gelatinized and cannot be viewed under this microscope
70
How to determine Mn
Mn: (Weight total)/(number total)
71
How to determine Mw
W: M x n Mw: (W1 x M1) + (W2 x M2) + (W3 x M3)/ W1 +W2 + W3
72
Polydispersity
Mw/Mn symbol is d Larger bandwith on SEC graph has a larger polydispersity
73
How to solve for Mw, Mn, polydispersity when given molecule in grams
This weight is the W value so plug value in grams into W value and solve
74
Size exclusion chromatography 2 types
Gel Filtration Chromatography Gel Permeation Chromatography
75
How does SEC work
Separates based on molecule weight or size and no interaction occurs
76
Ideal vs Non-Ideal Sec
Ideal: non interaction occurs Non-ideal: interaction between occurs between solute and support
77
SEC which molecules are eluted first
Large molecules
78
How to determine Mw using SEC
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
How to choose packing material for SEC
Consider purpose of separation and size of molecules
80
Relationship between elution volume and elution time
Elution volume = flow rate x time Linear function with a constant flow rate
81
How to use viscosity to determine Mw
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
Specific viscosity
(Viscosity of sample - solvent viscosity)/Solvent viscosity (T-T0)/T0
83
Intrinsic viscosity
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
SEC Packing Material
Hydrophobic media (cross linked polystyrene) Hydrophobic gels (polysaccharide-based packings)
85
Simple Coacervate vs Complex coacervate
Separation that occurs through salting out. Simple: Formed from a single polymer Complex: Formed from multiple polymers

Food Physical Systems (5 decks)

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