Huang Exam Flashcards
Pectin
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
Foam
Gaseous material dispersed through another material that is a liquid or a solid.
How is a stable foam formed
Surface Tension
Bread as a Foam
Has air bubbles that form from CO2 air bubbles that eventually evaporates and causes holes in bread that act as a foam
Amorphous structure
There is no molecular order, and physical properties can change by orders of magnitude at Tg (glass transition temperature)
Ex: extruded snacks
Glass transition temperature and the motions of molecules
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
Crystal structure
Molecules have long-range order and lower energy
Has sharp melting point peak
Semi-crystalline structure
Contains both amorphous and crystalline structures
Broad melting peak
Ex: Cellulose
Conformation of Starches
Amylose: linear starch and starch with high amylose content has higher crystallinity
Amylopectin: Branched Starch
Glycogen: Branched starch with a denser outer-region
Gelatinization of starch
Water absorbed in amorphous space -> number and size of crystalline region decreases -> amylose leaches into surrounding water
Native starch -> gelatinized starch -> retrograded starch
Polyphenols
Can act as antioxidants to work against lipid oxidation
How do antioxidants work against lipid oxidation
Stabilize free radical
Structures with more resonance are more stable (Ex: Benzene)
Polyphenols in Life
Anthocyanin in sweet potatoes has an oxygen with a + charge
If this is extracted, the purple is easy to degrade
What pH are polyphenols stable at
Acidic pH
Green tea to black tea
Under effects of fermentation (temperature and microorganisms), polyphenol changes to other Polyphenols with a higher molecular weight which is why the color changes
Thermodynamics
Temperature is related to thermodynamics
Provide energy
Ex: how much heat required for extrusion
Deals with direction in which a process occurs
Kinetics
Related to shelf life and quality of food
Thermodynamics and shelf life
Temperature determines kinetics through drying process
Storing a food at lower temperatures lowers rate if decay more efficiently
Phase diagram and phase transitions
Understand how to transition from one phase and temp to another and the math needed
Supercritical CO2 and subcritical butane in the food processing industry
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
Entropy
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
Putting Food in Freezer regarding Entropy
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)
Equation for Change in entropy system during temperature change
ΔS = Cp*Ln(Tf/Ti)
Cp of water is 75.7 J/K
Cp of Ice is 35.6 J/K
Equation for change in entropy system during phase change
ΔS = (ΔH/T)
H: Enthalpy (May need to be converted to Joules)
How to calculate total entropy of the system
ΔStotal = Sum of all ΔS values
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)
Equation for change in entropy of the surroundings during phase change
Qfreeze = -H(water)freeze
Free Energy Equation
ΔG = ΔH -TΔS
if ΔG > 0, process is spontaneous
if Δ < 0, process requires energy
Enthalpy driven process
ΔH < 0
Formation of bonds drives process
Fat Crystallization at low T
Gelatin gelation at 5 C
Condensation
Entropy Driven process
ΔS > 0
Increase in disorder drives process
Sugar dissolving in tea
Evaporation
Electrostatic interactions
H-bonding and electrostatic interactions can occur with a + charged protein and - charged polysaccharide
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
How to Solve for Keq
Keq = e^(-ΔG/RT)
R: 8.314 J/Kmol
make sure units match
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
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
Are foods at an equilibrium?
No
Chemical reactions (oxidation, hydrolysis) and physical structures (emulsions, gradients) are not at equilibrium
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
Phase separation
pH adjusted to below isoelectric point
coacervates and solution turns turbid
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
Coacervate in an aqueous solution
Water is a solvent
Protein will be salted out as concentration of salt increases
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
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
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
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
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
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
What is needed for a material to be extruded
Need to be processed above glass transition temperature but below degradation temperature
Ethylene as a polymer
Polyethylene and Polypropylene
The way ethylene is processed can give different results and properties
Free radicals and polymers
Free radicals can react with monomers that have double bonds to form an ongoing degradative reaction similar to lipid oxidation
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
Swelling with a good solvent
Polymer fully dissolves and swells
Has specific interactions between polymer and solvents
Theta Solvent
In-between swelling and compact structure
what structure do polymers in a poor solvent form?
Molecule forms compact structure
Does not have interactions between polymer and solvents
What are the four concentrations of a polymer in a solvent
Diluted solution
Semi-diluted solution
Concentration solution
Gel
Physical gels
Are reversible
Eggs are an example of a non-reversible gel
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
Synthesis of Polymer
Free radical polymerization and copolymerization
This process is similar to lipid oxidation
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
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
Polylactic acid
biodegradable and consumed by bacteria
Ring opening Polyester
Polyester reaction or a Polycarbonate reaction can lead to a chain of open ring structures
Notable Polysaccharide sources
Seaweed: agar, carrageenan
Plant cell wall soluble: pectin
Derived: modified starch
Polysaccharides by structure
Linear: amylose, cellulose, pectin, alginates
Short-branched: guar gum, locust bean gum, xanthan gum
Branch-on-branch: amylopectin, gum Arabic, arabinoxylan
Amylose/Amylopectin ratio
This ratio determines the properties of starch
More amyloses have more crystallization because amylose is a linear polysaccharide
Polysaccharides by monomers
Homoglycans: starch, cellulose
Diheteroglycans: agars, alginate carrageenan, carrageenan
Triheteroglycans: xanthan, gellan, arabinoxylan
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)
Starch
Semi-crystalline
Becomes gel during cooking
High on the Glycemic Index
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
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
How to determine Mn
Mn: (Weight total)/(number total)
How to determine Mw
W: M x n
Mw: (W1 x M1) + (W2 x M2) + (W3 x M3)/ W1 +W2 + W3
Polydispersity
Mw/Mn
symbol is d
Larger bandwith on SEC graph has a larger polydispersity
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
Size exclusion chromatography 2 types
Gel Filtration Chromatography
Gel Permeation Chromatography
How does SEC work
Separates based on molecule weight or size and no interaction occurs
Ideal vs Non-Ideal Sec
Ideal: non interaction occurs
Non-ideal: interaction between occurs between solute and support
SEC which molecules are eluted first
Large molecules
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
How to choose packing material for SEC
Consider purpose of separation and size of molecules
Relationship between elution volume and elution time
Elution volume = flow rate x time
Linear function with a constant flow rate
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
Specific viscosity
(Viscosity of sample - solvent viscosity)/Solvent viscosity
(T-T0)/T0
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
SEC Packing Material
Hydrophobic media (cross linked polystyrene)
Hydrophobic gels (polysaccharide-based packings)
Simple Coacervate vs Complex coacervate
Separation that occurs through salting out.
Simple: Formed from a single polymer
Complex: Formed from multiple polymers
