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YR2SEM1 > FOOD2150 Set 5 > Flashcards

FOOD2150 Set 5 Flashcards

1
Q

What are fats?

A
  • typically exist as mono-, di-, triesters of glycerol with fatty acid
  • mono,di,tri
  • recall: SN2 does not cleave, remains with triglyceride
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2
Q

How do lipids exist?

A
  • liquids (oils) or solids (fats)
  • non-polar organic compounds (soluble in organic solvents)
  • includes fats and oils, sterols, waxes, fat-soluble vitamins (ADEK)
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3
Q

What do fatty acids look like?

A
  • straight-chain aliphatic carboxylic acids
  • Fatty acids vary based on length, saturation, and type of saturation (all even numbered)
    Three main types of fatty acids
  • saturated fats (solids)
  • cis unsaturated fats
  • trans unsaturated fats
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4
Q

What are short- medium- and long-chain lipids?

A

short: 4-8
medium: 10-12
long: 16-20

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5
Q

What is the lipid nomenclature?

A
  • Start numbering from the carboxylic acid
  • Number in front indicates double bond position
  • Replace the alkane with alkene
  • For the alkanoic acid it becomes alkenoic acid
  • Two double bonds alkdienoic acid
  • Three double bonds alktrienoic aci
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6
Q

Compare Cis and Trans isomers

A

CIS:
- same side, naturally occuring
TRANS:
- different side, industrially occuruing

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6
Q

What is the only food with naturally occuring trans fats?

A

dairy: biohydrogenation in animals but
- not the same as the ones we regularly consume in our diet

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7
Q

What is partial hydrogenation?

A
  • double bonds changed to hydrogens to make more saturated
  • trans fat has similar MP to saturated fat
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8
Q

What are other types of distribution?

A

even/widest:
Fatty acids are as broadly distributed as possible
random:
- fatty acids are distributed randomly on within the triglycerides
- no preference on where in molecule FA located

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9
Q

What is fatty acid (restricted random) distribution?

A
  • not completely random or ordered
  • restricted random: ex cocoa butter (2/3 saturated)
  • preference is given to the position on the triglyceride
    *ex: one fatty acid may be more apt to reside at position 2 while it will be in lower quantities at position 1 and 3
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10
Q

What does melting point depend on for triglycerides?

A
  • degree of saturation and carbon length
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11
Q

What are semi-crystalline solids?

A
  • not true crystals (arranging in orderly and repeating manner that extend in 3 dimensions)
  • polycrystalline (composed of pieces of crystals).
  • semi-crystalline (not 100 % solid — contains
    amorphous oil phases)
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12
Q

What are the 2 stages of crystallization?

A
  • nucleation (formation of first crystals)
  • crystal growth (enlargement of nuclei)
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13
Q

Describe different liquid forms of lipid crystallization

A

alpha: lowest density and stability
beta prime: intermediate density and stability
beta triclinic: stable

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14
Q

What is supersaturation?

A
  • Lipids crystallize at temperatures lower than they melt
  • The temperature difference between the melting
    temperature and crystallization temperature is the
    supersaturation temperature
  • This undercooling is the thermodynamic driving force
  • defect: gravy fats
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15
Q

What are the 2 types of nucleation?

A

Homogeneous nucleation
- Large undercooling
- Nuclei appear at once
Heterogeneous nucleation (don’t like in food industry)
- Low undercooling
- Nuclei form in the presence of other nuclei (larger, different polymorphic in system)

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16
Q

What is crystal size and distribution?

A
  • final crystal size is a balance between the growth rate and the nucleation rate
  • small crystals are good: can’t detect, form larger network: liquid oil gets trapped, no phase separation (more nuclei= larger # small crystals)
  • Very important for final properties of fat (small have higher SA/V ratio)
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17
Q

How does packing affect alignment?

A
  • The α-form crystallizes initially under high supercooling
  • The more perfect the packing, the more
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18
Q

What is the tempering process?

A
  1. Melt all TAGs no crystals remain to “template” nucleation
  2. Cool the chocolate to get Form β-V nuclei
  3. Heat the chocolate to melt β’ polymorphs melt but not β-V
  4. Let chocolate “mature” so Form β-V nuclei grow
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18
Q

Describe polymorphism

A
  • identical TAGs can exhibit different crystal packing
  • affects many of the properties of fat materials
  • transformations are monotropic and occurs toward more stable species
  • Melt-mediated polymorphic transformations
  • Solid-state polymorphic transformations
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19
Q

What is bloom?

A
  • Is a physical imperfection in chocolate
  • Poor color & not glossy
  • Occurs due to uncontrolled recrystallization
    of the β-form V to β-form VI
  • accelerate by adding inclusions, and bad temperature handling
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19
Q

What is hydrolytic rancidity?

A

breakdown of triglycerides into glycerol and individual fatty acids
- MP, BP, smoke point drop
- free fatty acids breaking off triglyceride
- very carcinogenic when cooked with !

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20
Q

What is hydrolytic rancidity accelerated by?

A

water, lipases, agitation

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20
Q

Where is hydrolytic rancidity a problem?

A
  • Frying oils
  • Milk fats (Goat and cow especially)
  • Lauric oils (Coconut and palm kerne
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21
Q

How does lipase affect milk?

A
  • milk naturally rich in lipase (mechanism by which it cleaves)
  • Milk TAGs are highly asymmetric
  • SCFA always in the sn-3 position
  • Milk lipase is specific only for the sn-3
  • Lipases work at the water-oil interface
  • Pasteurize, then homogenize
  • Homogenization “exposes” w/o interface
  • Pasteurization deactivates lipases first (always pasteurize before homogenize)
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22
Q

What does hydrolytic rancidity require?

A
  • water
  • heat (or lipase)
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23
Q

What is lipid oxidation?

A
  • oxidative rancidity
  • addition of oxygen to unsaturated lipids
  • linoleic acid 10/40x more likely to oxidize than oleic
  • oxidation rate doubles with addition of double bond
  • most difficult reaction to control in foods and is main chemical reaction limiting shelf life of foods
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24
Q

What is the rate of oxidation?

A
  • thermodynamically non-spontaneous (requires initiator to make first L radical)
  • rate of oxidation is dependent on how quickly an electron is extracted
  • e easily extracted with DB, and if they’re methylene interpreted
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25
Q

Describe the initiation of lipid oxidation

A
  • The removal of a hydrogen atom from a fatty acid to form a fatty acid radical or “alkyl radical”
  • Resonance stabilization = stabilization of structure by movement of electrons.
  • Resonant stabilized structures form more easily.
  • ease of initiation characterized by dissociation energy: high diss. energy: more stable, low diss. energy: less stable
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26
Q

Describe the propagation and chain branching of lipid oxidation

A
  • Transfer of free radicals from one lipid to another propagates the reaction
  • Peroxyl radicals (LOO*) can abstract (pull off) a hydrogen from a neighboring molecule
  • Unstable lipid hydroperoxides (LOOH) are formed in the process.
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27
Q

Describe the hydroperoxide breakdown of lipid oxidation

A
  • The end-product of primary oxidation, hydroperoxides, ROOH, are very unstable
  • ROOH can decompose into: alkoxy radical (RO·) and hydroxyl radical (·OH)
  • The alkoxy radical (RO·) is even more reactive than the alkyl or peroxy radicals
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27
Q

Describe the termination-beta-scission of lipid oxidation

A
  • Alkoxy radical “steals” an electron from a neighboring bond
  • Breaks apart the alkyl chain:
  • Aldehydes and more alkyl radicals form
  • Repeated β-scission can generate a mind-boggling array of products
  • The more double bonds, the smaller the secondary oxidation products
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27
Q

Describe the termination of lipid oxidation

A

R· + R · → R2
R· + ROO· → ROOR
ROO· + ROO· → ROOR +O2
- Termination concurs with oxidation slowing and stable
products accumulating
* At this stage, rancidity detectable
* Lipid free radicals form non-radical products by two major mechanisms: radical recombination, scission reactions when proton sources (water) are present to stabilize products

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27
Q

Describe the termination of lipid oxidation

A
  • Free radicals cause the break down to small compounds such as ketones and aldehydes
  • These react with other components in foods producing
    amines
  • Cause off flavours and odours
  • The aldehydes and ketones small compounds can
    polymerize increasing the viscosity of oil
28
Q

What is a primary antioxidant?

A
  • chain-breaking
  • Reacts with alkyl, peroxy and alkoxy radicals
  • Prevents propagation by breaking the chain
    reaction
  • Usually contains a phenol group
  • major structural requirements: must donate a H and stabilize free radical (conjugation, stearic hindrance, new covalent bond)
29
Q

What is a secondary antioxidant?

A
  • preventive
  • Do not react with radicals
  • Deactivate pro-oxidants
  • Quench UV light
29
Q

How do primary antioxidants stabilize by resonance?

A
  • double bond conjugation
  • Linear or cyclic alternating single and double bonds
  • Allows dislocation of the unpaired electron
30
Q

How do primary antioxidants stabilize stearically?

A
  • bulky electron clouds shield free radical: BHT
  • Once the antioxidant donates a hydrogen and electron to the radical, the antioxidant becomes a radical
  • Antioxidant radicals must be stable
  • “Resonance stabilized” delocalization of unpaired electron around a phenol ring
  • Antioxidant radicals undergo termination
    reactions with other radicals readily (free
    radical scavenging)
31
Q

What are the goals of hydrogenation?

A
  • Makes oil more stable by removing unsaturated double bonds (frying oils)
  • Converts cis-unsaturated fatty acids to either saturated or trans-unsaturated fatty acids
  • Changes the physical properties of an oil from a liquid to a solid (margarine)
31
Q

How did hydrogenation first start?

A
  • adapted from petrochemical industry
  • first food oils: on whale and fish oils
  • Marine oils are highly unstable due to highly unsaturated fatty acids
  • Marine oils contain few natural antioxidants
32
Q

How can we hydrogenate an oil?

A
  • H2 gas (dangerous)
  • Pressurized reaction (414 kPa typical, max < 1000 kPa)
  • High temperatures: 250oC to 300oC
  • Catalyst (usually nickel).
  • Reaction Time: 40 to 60 minutes
32
Q

Describe steps 1-2 of oil hydrogenation with nickel

A
  • The double bond interacts with the metal catalyst by virtue of its π electrons.
  • Hydrogen is adsorbed (or may already have been prior to #1) to the surface of the metal catalyst.
33
Q

Describe steps 3-4 of oil hydrogenation with nickel

A
  • An adsorbed hydrogen atom is transferred to a carbon
    participating in the double bond while the other carbon is σ-bonded to the catalyst
  • Transfer of a second hydrogen atom to the σ-bonded liberates the fatty acid from the catalyst.
  • No H present: lipids come away from catalysis, remains in saturated state
34
Q

How does the fatty acid % affect the time for hydrogenation?

A

more double bonds: less time for fatty acid %
lineolenic < linoleic < oleic < stearic

35
Q

What is partial hydrogenation?

A
  • Isomerization always occurs (undesirable)
  • Geometrical: cis- double bonds become trans- double bonds and vice versa
  • Positional: The location of the double bond shifts over by one carbon up or down the chain
  • not used in canada, little importance in food industry
  • we dont fully hydrogenate fish oil, or all of its use would be gone
36
Q

What is full hydrogenation?

A
  • Run to completion (solid fat)
  • No unsaturation remains
  • All fat is saturated at this point
  • still important in food industry
37
Q

How do we avoid partial hydrogenation?

A
  • we do not partially hydrogenate, we get more transalatic acid (18:1 in trans form)
  • so we pump a lot more hydrogen in, so we know it is saturated with hydrogen
38
Q

What is the tristearin-vast majority?

A
  • very difficult to work with
  • If you mix it with oil, it is very grainy
  • Good for frying oils
39
Q

What is interesterification vs intraesterification?

A

inter: substitutes fatty acids on different glycerol molecules; moves position and glycerol
intra: intra: randomizes it on one fatty acid, not glycerol

39
Q

What is atherosclerosis (arterial hardening)?

A
  • plaque deposited on the inside walls of blood vessels, specifically arteries (presence of high shear
    – promotes injury; and free radicals
    – promotes oxidation of LDL and generation of foam cells)
40
Q

What is plaque (atheroma)?

A
  • made up of foam cells: lipids (especially oxidized LDLs) + white blood cells (macrophages) + calcium (hardening)
  • Plaque is very insoluble (need special enzymes to dissolve them)
  • Plaques are started by LDLs binding to blood vessel walls, perhaps for repair
41
Q

Describe interesterification and what it is used for

A
  • a process that rearranges the fatty acids in a fat or oil, typically a mixture of triglycerides
  • remove partially hydrogenated fat
42
Q

Describe intraesterification and what it is used for

A
  • the process of shuffling fatty acids within a triacylglycerol (TAG) molecule
  • create soft fats
43
Q

What are the aliphatic side-chains of AA?

A
  • to not ionize, only have H and C
    G: H-
    A: CH3-
    V: (CH3)2CH-
    L: (CH3)2CHCH2
    I: CH3Ch2Ch(CH3)
    P: cyclic; -Ch2CH2CH2-
44
Q

What are the polar neutral side chains AA?

A
  • side chains do not ionize under biological conditions
    S: HOCH2-
    T: CH3CHOH-
    N: NH2COCH2-
    Q: NH2COCH2CH2-
45
Q

What are the sulfur-containing side chains AA?

A

C: HSCH2-
M: CH2SCH2CH2-

46
Q

What are the aromatic side-chain AA?

A
  • side chains do not ionize
    F: C9H11NO2
    Y: C9H11NO3
    W: C11H12N2O2
47
Q

What are the cationic side-chains AA?

A

H: C6H9N3O2
K: C6H12N2O2
R: C6H14N4O2

48
Q

What are the anionic side-chains AA?

A

D: -O2CCH2-
E: -O2CCH2CH2-

48
Q

What is a protein-zwitterion

A
  • Molecule having separate positively and negatively charged groups
  • Molecule has NO NET charge
49
Q

What is a protein-peptide bond?

A
  • upstream AA with downstrea AA: dehydration synthesis forms amide with a peptide bond
  • R-groups alternate in trans conformation
50
Q

Describe the protein-peptide bond

A
  • covalent bound via peptide bond (loss of water)
  • pi-pi bond delocalizes between C=O
  • C-N occur as C=N and both behave as DB
  • bond is rigid and planar, rotation from alpha C
51
Q

Describe key points of the primary structure of a protein

A

= controlled at genetic level
- not modified by physical changes; through hydrolysis or post-translational chemical modifications
1. length of AA dictates molecular weight
2. similarity in composition doesn’t = sequence similarity

51
Q

Describe key points of the secondary structure of a protein

A
  • The local conformation of the polypeptide backbone (molten globule structure)
  • Sections of the polypeptide strand “self-organize” into β-sheets and α-helices
  • The rigid planar amide bond is crucial for secondary structure as it limits the
    conformations that amino acids can assume
52
Q

Describe the a helix of a protein secondary structure

A
  • 3.6 AA per helical turn
  • 13 atoms H-bonded in ring
  • N-H H bonds with C=O 4 residues earlier
  • M, A, L, E, K, R, Q, H
  • defined as i+4-> i
52
Q

Describe the alpha-helix

A
  • most common conformation
  • stabilized by H-bonding of all the carboxylic acid and amino groups on the 4AA apart on the polypeptide backbone
  • Each amino acid has a rise of 1.5A and a 100o rotation which leads to 3.6 amino acids per twist of the -helix
  • With a 100o rotation per amino acid two adjacent amino acids are on opposite sides of the helix
53
Q

Describe the b sheet of a protein secondary structure

A
  • basic unit is continuous sequence of amino acids (β-strand)
  • 5 - 15 AA
  • β-strands interact via hydrogen bonding to form a β-pleated sheet
  • Unlike the α-helix, the hydrogen bonds are not intrasegment but are intersegmental
  • Y, F, W, Y, I, V, C
53
Q

Compare anti-parallel and parallel B-sheets

A

anti: opposite biochemical direction
- H-bonds formed without any angle
parallel: same biochemical direction
- H bonds formed at angle

54
Q

Describe B-turns of proline

A
  • Molecular configuration does not allow formation of secondary structure
  • No hydrogen atom at the α-NH2 for H-bonding
  • Proline disrupts α-helices and β-sheets
  • Proline is found as the first residue of an
    α-helix & at the edge strands of β-sheets
  • Proline is common in loop sequences
54
Q

Describe B-turns of glycine

A
  • No side chain carbons to prevent water from hydrogen bonding
  • No bulky sidechain to drive β-sheets
  • Glycine breaks α-helices
  • Glycine is common in loop sequences
55
Q

What is the tertiary structure of protein stabilized by?

A
  • Disulfide Bridges (Covalent)
  • Salt Bridges (Electrostatic)
  • Hydrogen Bonds (Permanent Dipoles)
  • Van der Waals Forces (Transient Dipoles)
56
Q

What is protein folding driven by in the tertiary protein structure?

A
  • hydrophobic effect
  • For water to interact with hydrophobic residues water must form clathrates
  • Clathrates are cage-like structures of water arranged to cancel waters dipole moment
57
Q

What is the protein function determined from?

A
  • its 3 structure
58
Q

What are most structural vs functional proteins?

A

structural:
- fibrous (insoluble in water)
- collagen, hair and wool, myosin, fibroin
functional:
- globular (soluble in water)
- most enzymes
- ovalbumin, whey proteins

59
Q

Describe myoglobin as a quaternary structure

A
  • water soluble animal pigment
  • hemoglobin is 4 myoglobin with Fe2+, making a quaternary structure
60
Q

What causes structure loss in proteins?

A

DENATURING AGENTS
- heat
- pH
- ionic strength
- solvent polarity
- shear

61
Q

What denatures?

A
  • secondary, tertiary, quaternary protein structures
  • native structure for most proteins only marginally stable; function of protein’s environment
62
Q

How can denaturation be desirable or undesirable in food?

A

Desirable: Fried egg, trypsin inhibitors, foaming, emulsification
Undesirable: Pale, Soft, Exudative meat (pork)

63
Q

What are some examples of protein functionality?

A
  • Texture of meat
  • Thickness of yogurt
  • Stability salad dressings
  • Gelation of Jell-O & fried egg
  • Texture of bread products
64
Q

What happens to a protein when it undergoes denaturation?

A
  • exposes hydrophobic groups to water decreasing solubility
  • Proteins interact via hydrophobic interactions
  • Heat can cause formation of di-sulfide bridges
65
Q

What are the physical properties of denatured proteins?

A
  • Decreased solubility (aggregation and gelation)
  • Decreased biological/enzymatic activity
  • Increased digestibility (exposure to enzymes)
  • Increased viscosity (higher hydrodynamic
    volume)
  • Increased water-binding
66
Q

What are the two proteins essential to wheat’s texture in baked wheat products?

A

Glutenin (high molecular mass): responsible for the strength and elasticity of dough
Gliadin (monomeric (low molecular mass)): responsible for the extensibility of dough

66
Q

What is a zymogen?

A
  • inactive precursor of an enzyme requiring a biochemical change for it to become an active enzyme
  • Essential to prevent self-digestion

YR2SEM1 (10 decks)

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