Midterm Review Flashcards
1
Q
What is the difference in terms of structure between liquid and solid waxes? Give examples of both.
A
Liquid wax: short-chain (ex: jojoba oil)
Solid wax: long-chain
2
Q
In phospholipids, what is the structure called when X=OH?
A
Phosphatidic acid
3
Q
In phospholipids, what is the structure called when X=O-CH2-CH2-NH2?
A
Phosphatidylethanolamine
4
Q
In phospholipids, what is the structure called when X=O-CH2-CH2-N+(CH2)3
A
Phosphatidylcholine
5
Q
In phospholipids, what is the structure called when X=O-CH2-CH(NH2)-COOH
A
Phosphatidylserine
6
Q
In phospholipids, what is the structure called when X=sugar
A
Phosphatidylinositol
7
Q
What are the three classes of phospholipids?
A
- Lecithins (Phosphatidylcholines)
- Cephalins (Phosphatidylethanolamines)
- Phosphatidyl inositols
8
Q
How do short-chain fatty acids and long-chain fatty acids differ in terms of their contributions to flavour?
A
Short-chain FA: contribute to flavour
Long-chain FA: have no flavour per se BUT they will give a soapy flavour in the presence of salts
9
Q
The presence of ________ can lower the smoke point of edible oils when used for frying.
A
free fatty acids
10
Q
What does this structure correspond to?
CH3-(CH2)n-CH2-OH
How many carbons do they need to have at least?
A
- Alcohols
- At least 6 carbons
11
Q
Short-chain ______ are often major contributors to flavour.
A
alcohols
12
Q
How many carbons does a fundamental isoprene unit contain?
A
5 carbons
13
Q
What are terpenes components of?
A
Components of the fragrant oils obtained from leaves, flowers and fruits
14
Q
What are the main constituents of essential oils?
A
Monoterpenes, with sesquiterpenes
15
Q
How many isoprene units and carbons do these terpene classes contain: A) Monoterpenes B) Sesquiterpenes C) Diterpenes D) Sesterterpenes E) Triterpenes
A
A) 2, 10 B) 3, 15 C) 4, 20 D) 5, 25 E) 6, 30
16
Q
What is the main mechanism for oils becoming plastic fats?
A
cis -> trans conversion during hydrogenation
17
Q
Differentiate unconjugated and conjugated double bonds.
A
Unconjugated: separated by methylene group (natural state of most fatty acids)
Conjugated: double bonds are next to each other, not interrupted by a methylene (CH2) group (not naturally found)
18
Q
What does a mixed bonding system lead to? Where is that positioned?
A
- Leads to formation of an ACTIVE METHYLENE group
- Positioned between a conjugated and unconjugated double bonds
19
Q
The omega nomenclature is based on two assumptions. What are they?
A
- All natural fatty acids are in the cis form
- The double bonds will be always be UNCONJUGATED
20
Q
Arachidonic acid, C__, with __ unconjugated double bonds, the first double bond in position _, the next at _, _, and _, respectively
A
- C20
- 4 unconjugated double bonds
- 6, 9, 12, 15
21
Q
What group does Erucic acid belong to?
A
Omega-9
22
Q
What group does arachidonic acid belong to?
A
Omega-6
23
Q
There are no simple, analytical methods for separating, isolating and identifying individual _________.
A
triglycerides
24
Q
In plant seeds, what kind of lipids are used as a source of energy for germination?
A
Triglycerides
25
What lipid is responsible in part for the desirable flavour of aged cheese?
Short-chain fatty acids
26
How many carbons does the lauric acid group contain?
12
27
What are the sources of the lauric acid group?
- Oil palm (tropical oils)
| - Palm kernal oil, coconut and babasu
28
How does palm kernal oil differ from palm oil?
- Palm kernal oil (extracted from palm oilseeds)
| - Palm oil (from palm fruit), which is much more highly unsaturated and is not part of the lauric acid group
29
Are lauric acids solid or liquid at room temperature?
- Although largely saturated
| - They are oils owing to the high proportion of C12 fatty acids in their triglycerides
30
What kind of fatty acids are resistant to oxidative rancidity? Which group is an example of this?
- Low degree of unsaturation
| - Lauric acid
31
Most oils in this group tend to be categorized as industrial "drying oils". Which group does this passage refer to?
Linolenic acid
32
Why are linolenic acids sometimes referred as "drying oils"?
Because of their ability to polymerize into a hard film if applied as a thin layer on surfaces (paint)
33
The polymerization capability is present in all _____________ oils, but those containing high levels of _____________ are more reactive
unsaturated oils, linolenic acid
34
What are common examples of the linolenic acid group?
Soybean, linseed, castor, hempseed and perilla oils
35
Processed soybean oil, if stored after extraction without modification, suffers from a problem commonly termed _______.
Reversion
36
What is reversion?
Relatively rapid transition from a bland, tasteless oil shortly after processing to a grassy, hay-like and then fishy flavour
37
How is reversion overcome? What fats are converted to what?
By hydrogenation to convert a substantial portion of linolenic to oleic and linoleic acids
38
Animal fat depot group has a higher ratio of what compared to the oleic-linoleic acid group?
Di-saturated (gs2u) and tri-saturated (gs3) glycerides
39
Some fish oil fatty acids can be highly unsaturated. Up to how many double bonds do they contain?
Up to 6 double bonds
40
What are two examples of the erucic acid group?
Rapeseed oil and mustard oil
41
How was rapeseed oil used originally?
Used extensively as a marine motor oil
42
What allows the separation of cis from trans isomers?
Silver ion chromatography
43
What kind of lipid is biodiesel?
Methyl esters
44
Which fatty acid group is useful in cosmetics?
Lauric acids
45
What is the fatty acid breakdown of olive oil?
- Oleic (75%) - M
- Palmitic (10%) - S
- Linoleic (10%) - U
46
What is the first step of the processing of oilseeds?
- Crush the oilseed
| - Give the crush a heat treatment
47
What does the heat treatment of a crush do?
Aids in knocking out the enzymes lipase and lipoxygenase, which can cause a deteriorative reaction
48
What deteriorative reactions do lipases cause? How? What are they present in?
- Lipolysis
- Hydrolysis of the ester linkage between glycerol and a fatty acid in the TG
- Enzyme present in every living system
49
What deteriorative reactions do lipoxygenase cause? How?
- Autoxidation
| - Oxidation of polyunsaturated fatty acid chains that have a cis,cis-1,4-pentadiene group (e.g. linoleic and linolenic)
50
In the case of fats and oils from animal and fish sources, what is the most common method of processing?
Rendering
51
What are the four steps most oils go through following extraction?
1) Settling/degumming
2) Refining
3) Bleaching
4) Deodorizing
52
What is the use of settling/degumming? What does it get rid of?
- Carbs, proteins and phospholipids hydrate and associate themselves with the aqueous phase
- Over time, aqueous phase separates from the oil, carrying with it the cellular debris, carbs and phospholipids
53
In the settling/degumming phase of soybean oil, what is recovered from the aqueous layer? Why?
- The phospholipids since soybeans contain 5-8% phospholipids (mainly lecithin)
- They have commercial value as emulsifiers
54
What does refining remove?
Removes the free fatty acids from the oil
55
What does bleaching remove?
Designed to remove the coloured material from the oil (carotenoids, chlorophyll, and pheophytin)
56
What does deodorization remove?
Removes the volatile compounds that give the oil off-flavours
57
In olive oil, what compounds are not removed for the best quality? Which steps are not used?
- Flavour and colour compounds
| - Only pressed; bleaching and deodorization are not used
58
Define selectivity. It is a property of what?
- Preferentially hydrogenating more highly unsaturated fatty acids
- Property of the catalyst
59
What is proprietary?
Knowledge of conditions and selectivity characteristics provides control
60
What causes lard to be "grainy"?
In lard, the GS2U component is largely made up of oleopalmitostearin, which has a propensity to form large crystals.
61
How can the structure of lipids in human milk be reproduced artificially?
Enzymatic interesterification reaction using sn-1,3 specific lipase as a catalyst.
62
Why can fat have plasticity or spreadability?
Because a fat is made up of a liquid in a crystalline matrix
63
The crystalline matrix of fat forms a 3-D network that holds the system together by what force? How does it explain plasticity?
- Van der Waals forces
| - Because they are weak forces, they can be broken and readily re-formed again
64
When a fat can be deformed readily, it is said to be in what range?
Plastic range
65
How is the solid fat content commonly determined?
- Dilatometry
| - Nuclear magnetic resonance (NMR) measurements
66
What is plotted in dilatometry?
The specific volume is plotted as a function of temperature
67
What do the 3 curves in the specific volume over temperature graph represent?
A) Thermal expansion of the solid fat
B) Expansion due to a change in state
C) Thermal expansion of the liquid only
68
How does the pulsed NMR SFC measurement work?
- Sample of fat is placed in a magnetic field
| - Radiofrequency (RF) pulse is applied perpendicular to the field to "tip" the spins
69
What is the signal accompanying the relaxation process of the 1H magnetic spins after they are disturbed by the RF pulse?
FID (free induction decay)
70
Which spins of the 1H nucleic relax more rapidly? Compared to what?
Spins in the solid state relax more rapidly than those in the liquid phase
71
What is polymorphism? What exhibits it?
- The occurrence of several different crystal forms for a single compound
- Triglycerides
72
What are the most common polymorphic forms in order of relative stability?
Alpha (a), beta prime (B'), and beta (B)
73
How do alpha, beta-prime, and beta polymorphs differ in terms of the cooling of liquid fat?
Alpha: rapid cooling of liquid fat
Beta-Prime: slow cooling of liquid fat
Beta: very slow cooling of liquid fat
74
What are the four methods for conversion from Beta to Beta-prime?
- Interestification
- Hydrogenation
- Winterization (destearinization)
- Addition of cottonseed oil and/or tallow flakes (beta‐prime)
75
Does the volume increase or decrease as the temperature increase?
Volume increases
76
How do the triglyceride polymorphs compare in terms of their long spacing?
Alpha: longest long spacing
Beta-Prime: intermediate
Beta: shortest long spacing
77
How do the triglyceride polymorphs compare in terms of their packing?
Alpha: more loosely packed
Beta-Prime: more closely packed
Beta: most closely packed
78
What do the microscopic analyses of the triglyceride polymorphs reveal?
Alpha: platelet (5u)
Beta-Prime: fine needle (1 u)
Beta: long needle (25-50 u)
79
What does the infrared spectroscopic analyses of the triglyceride polymorphs reveal?
Alpha: singlet at 720cm^-1
Beta-Prime: doublet at 719 and 727 cm^-1
Beta: singlet at 717 cm^-1
80
How do the triglyceride polymorphs differ in terms of stability and melting point?
Alpha: most unstable, lowest melting point
Beta-Prime: unstable, intermediate melting point
Beta: most stable, highest melting point
81
What does the color analyses of the triglyceride polymorphs reveal?
Alpha: translucent
Beta-Prime: in-between
Beta: opaque
82
Why is the specific volume of alpha high?
Since it does not pack well
83
What are high temperature base catalysts used in interesterification?
KOH and NaOH
84
What are low-temperature catalysts used in interesterification?
Sodium methoxide (NaOCH3)
85
What does the base catalyst do in interesterification?
Initial removal of an a‐proton by the base catalyst leads to the charge‐delocalized enulate anion.
86
In the interesterification of lard, what do conditions that favor intramolecular interchange result in?
Crystal-modified lard (CML)
87
In the interesterification of lard, conditions that favor random distribution can be controlled to yield what?
Partially modified lard (PML)
88
In the interesterification of lard, conditions favoring directed interesterification can be used to control what content? Of what lard?
GS3 content of direct interesterified lard (DIL)
89
Compare the solid fat index of directed, natural and randomized lard.
- Directed has the highest amount of solid fat (more plasticity)
- Randomized, similar to natural, higher though
- Natural: very low solid fat
90
How do you determine how many double bonds are lost during hydrogenation (catalyst activity)?
Defined as decrease in iodine number per unit of time during a hydrogenation under a specific set of conditions
91
What is the iodine number?
Defined as the number of grams of iodine absorbed by 100 grams of fat.
92
What are the five steps in the hydrogenation of oils?
1) Transfer and/or diffusion
2) Adsorption
3) Hydrogenation/Isomerization
4) Desorption
5) Transfer
93
Which steps are critical for controlling the degree of isomerization and selectivity of reactions in hydrogenation?
- Transfer/Diffusion
| - Adsorption
94
How can selectivity be expressed?
- Ratio Klo/Ko
| - The rate of hydrogenation of linoleate relative to that of oleate
95
What are the two types of catalysts for hydrogenation?
- Nickel catalyst
| - Copper-Chromium catalyst
96
How does the AOCS determine catalyst activity?
Time required to hydrogenate soybean oil to an iodine value of __ from ___ at ___oF, __ psig, ____%
catalyst concentration compared to the time required using AOCS standard catalyst under the same conditions.
Time required to hydrogenate soybean oil to an iodine value of 80 from 120 at 350oF, 20 psig, 0.05%
catalyst concentration compared to the time required using AOCS standard catalyst under the same conditions.
97
What are the independent variables that affect hydrogenation?
- Pressure
- Temperature
- Agitation
- Catalyst concentration
98
What are the dependent variables that affect hydrogenation?
- trans fatty acids
- Selectivity ratio
- Hydrogenation rate
99
If the pressure increases in hydrogenation, how is the selectivity ratio, the trans content, and the reaction rate affected?
Selectivity Ratio: Decrease
Trans content: Decrease
Reaction Rate: Increase
100
If the agitation increases in hydrogenation, how is the selectivity ratio, the trans content, and the reaction rate affected?
Selectivity Ratio: Decrease
Trans content: Decrease
Reaction Rate: Increase
101
What is the saponification value?
- The number of milligrams (mg) of potassium hydroxide (KOH) required to neutralize the fatty acids resulting from the complete hydrolysis of 1 g of the sample.
- mg of KOH required to saponify 1 gram of fat
102
How many mg of KOH does it require to saponify 1 mol of TG? How do you calculate the SV?
- 168 000 mg
| - SN = 168000/MW(TG)
103
In shortenings, how does the proportion of palmitic acid change? Which position?
The proportion of palmitic acid in the 2-position is reduced from about 64% to 24% on random interesterification.
104
Which fats have greater shortening abilities? How are they prepared?
- Fats with higher levels of unsaturated fatty acids
| - Often prepared by hydrogenation of vegetable oils
105
Which fat is a natural shortening? What does its quality depend on?
- Lard
| - Quality depends on the dominant crystal form and its solid fat content
106
How do beta-prime crystals incorporate air?
Large amount of small air bubbles; creamier, uniform and glossy shortenings
107
What is tempering?
Holding a fat at a temperature and for an amount of time that permits transformation to the desired polymorphic form.
108
What must be removed during tempering? Why?
The heat of transformation must be removed to avoid melting and a later conversion into large beta crystals.
109
What determines characteristic cocoa butter texture?
POS
110
What happens when POS (palmitic, oleic, stearic) is converted from beta-prime to beta?
Chocolate "bloom" - white spots and dull surface appearance
111
What is the key to the self-propagating nature of the autoxidation reactions?
Peroxy radical has a preference for terminating its radical state by abstracting a hydrogen from another fatty acid
112
What is the precursor molecule for compounds that are responsible for off-flavours?
Hydroperoxides
113
What are the primary oxidation products? (2)
- Hydroperoxides (R-O-O-H)
| - Peroxides (R-O-O-R)
114
When does the monomolecular hydroperoxide breakdown predominate? When does the bimolecular predominate?
Monomolecular: when hydroperoxide concentration is LOW
Bimolecualr: when hydorperoxide concentration is HIGH
115
How does the alkoxy radical decompose? (3)
- Aldehyde generation
- Alcohol generation (direct)
- Formation of a ketone
116
What does the peroxy radical prefer to do?
Prefer to abstract a hydrogen from a fatty acid (propagation radicals)
117
What is the definition of the peroxide value?
milli-equivalents (mEq) of peroxide oxygen per 1000 grams of fat.
118
What is the induction period?
- Slow initial accumulation of hydroperoxides
| - Predominantly the monomolecular reaction
119
Why does PV fall off later on?
Due to the fact that the decomposition of hydroperoxides is outpacing their formation
120
What does malonaldehyde react with in the TBA test? What does it produce?
- Reacts with 2 molecules of TBA
| - Produces a red complex, which can be readily assessed spectrophotometrically
121
Why are molecules with double bonds more susceptible to abstraction of a hydrogen?
- Because the LIFETIME of the free radical formed is extended significantly
- Electrons from the double bonds can resonate and stabilize the free radical structure
122
Positional cis/trans isomers occur as ________ form and decompose.
Peroxy radicals
123
Which oil is found naturally in the unconjugated form, but is readily converted into a mixed bonding system?
Linolenic acid
124
Where is the most unstable hydrogen in an oil?
The hydrogen from the methylene carbon
125
What is reversion?
- Rapid onset of rancidity without an apparent rise in the peroxide value
- An accelerated oxidation reaction, which does not allow hydroperoxides to linger
126
What is the major function of true antioxidants?
Have the property of being able to interrupt the PROPAGATION step of the autoxidation process
127
What do antioxidants typically give their free radical to?
Generally a peroxy radical
128
What do antioxidants lengthen?
They lengthen the induction period
129
What is the antioxidant legal limit? What is it based on?
- Under 0.02% (200 ppm)
| - Based on the fat content of the product
130
Metal ions shorten the ____________ and increase the overall __________
induction period, rate of the reaction
131
Does metal ion catalysis favour the second or third oxidation state reaction? What does it form?
Favours the second oxidation state; forms an alkoxy
132
What does the third oxidation state of a metal ion form?
A peroxy
133
What does the chelation of metal ions cause?
- Causes STERIC HINDRANCE
| - Eliminates the catalytic role metal ions would otherwise play
134
Where is lipoxygenase relatively abundant? What is it responsible for?
- In plant tissues
| - Responsible for the development of characteristic flavours
135
What do enzymes catalyze in the lipid of plant tissues?
- Catalyzes the formation of hydroperoxides
| - Instigates the free radical mechanism
136
What does the bleaching of pigments (chlorophyll, beta-carotene) occur as a result?
Result of autoxidation initiated by lipoxygenase
137
How does the nature of triplet and singlet oxygen compare?
Triplet: diradical
Singlet: no radical
138
How does the reaction of triplet and singlet oxygen compare?
Triplet: radical
Singlet: electron-rich
139
Photosynthesizers absorb light in the ____ - ____ range
380-900
140
The singlet state is produced first by the _______________, but it has a _____ lifetime, decaying to _______________ to the ground state and by _________________ to the triplet state
light absorbed
short
fluorescence
intersystem crossing
141
Lipoxygenase exhibits substrate specificity for what?
cis-cis-penta-1,4-diene unit
142
What is the role of preventative antioxidants?
Minimizes the formation of initiating radicals
143
Name some preventative antioxidants.
- Superoxide dismutase
| - Catalase
144
What is the role of radical scavenging antioxidants?
Breaks the free radical chain reactions by donating hydrogen to free radicals (Vitamin C, Tocopherol)
145
___________ are opposite to synergists.
Pro-oxidants
146
Give examples of metal chelators.
- EDTA (very efficient)
- Citric acid
- Phosphoric acid
147
What does the Benzidine test indicate?
If you have a yellow measurement, you have aldehydes in your oil
148
What does the TBA test indicate?
If you have an intense red colour, you have aldehydes in your oil (extensive oxidation)
149
What does the AOM method determine? What does it mean?
- Oxygen is bubbled at a controlled rate
- You can determine if the oil is prone to reversion within minutes
- Active Oxygen Method
150
Do efficient antioxidants have low or oxidation potentials?
High
151
Do efficient antioxidants have low or high reduction potentials?
Low
152
Name 3 factors that affect your choice of antioxidant.
- Safety
- Off-odor
- Stability to pH and food processing
153
In milk fat, long chain fatty acids are preferred in which positions?
- sn-1
| - sn-2
154
In milk fat, short-chain fatty acids are preferred in which positions?
sn-3
155
What kind of TG are preferentially synthesized in milk fats?
TG with one short and two long-chain FA
156
TG are contained within ___________ that are surrounded by a _________
- fat globules
| - membrane
157
_________ are synthesized by the microflora of the cow, and present health benefits
Conjugated linoleic acid (CLAs)
158
What are the components of the membrane that surround the fat globules in milk fats?
- Protein (41%)
- Phospholipids and glycolipids (30%)
- Cholesterol (2%)
- Neutral glycerides (14%)
- Water (13%)
159
How much cholesterol does milk, shrimp, and eggs contain?
- Milk: 27 mg
- Shrimp: 125 mg
- Eggs: 275 mg
160
What does the membrane that surrounds the fat globules in milk contain?
- Double layer of lipoproteins
| - Enzymes, including lipase
161
What is the function of the membrane of the fat globule
Prevents lipolysis
162
What is the consequence of the disruption of the membrane of fat globules? In which situation could this happen?
- Homogenization of milk
- Allows lipase to bind to the fat globules and to hydrolyze TG at a high rate
- Milk becomes unpalatable
163
What must be done prior to homogenization? Why?
Lipases must be inactivated by pasteurization to avoid them hydrolyzing the TG
164
What is lactose degraded to during ripening? How?
Degraded to lactic acid by homofermentation
165
What is a prerequisite for good aroma in cheese? What are the exceptions?
- As little lipolysis as possible
| - Exceptions: stinky cheeses (ex: roquefort)
166
What is the % of total monounsaturated lipids in red meat? Which fatty acids are the most present?
- Total: 50%
| - Oleic (18:1) > Palmitoleic (16:1)
167
What is the function of cholesterol in red meat? How much is found in 100 grams?
- Integral component of cellular membranes
| - 70-90mg/100 grams
168
What is the main polyunsaturated fatty acids found in skeletal muscles of red meat? What is the main source of saturated? What is the main source of unsaturated?
- Polyunsaturated: Linoleic acid
- Monounsaturated: Oleic acid
- Saturated: Palmitic and stearic acid (2:1 ratio)
169
What is the ratio of LDL to HDL in egg yolks?
LDL: 68%
HDL: 14%
170
Does LDL or HDL contain phosvitin? What is it?
- HDL
| - Phosphorus-rich, lipid-free protein
171
Associate these words:
1) LDL
2) HDL
A) Lipovitellin
B) Lipovitellenin
LDL: Lipovitellenin
HDL: Lipovitellin
172
What are the three main components of egg yolk phospholipids?
- Phosphatidylcholine/Lecithin (73%)
- Phosphatidylethanolamine/Cephalin (15%)
- Lysophosphatidylcholine (6%)
173
What leads to discolouration of dried whole egg and loss of palatability?
The reaction between cephalin and glucose (Maillard)
174
Fish is an important contributor to what types of omega-3 fatty acids? What are the benefits and downsides?
- Omega-3-polyenic acids (5 or 6 double bonds)
- Nutritional value
- Preservation is difficult because of their easy peroxidation
175
What is the fatty acid profile of soybean oil?
- Saturated FA (14%)
| - Unsaturated FA (81%)
176
What is the main saturated FA in soybean oil? What are the main unsaturated FA in soybean oil?
- Palmitic acid (10%)
- Linoleic acid (51%)
- Oleic acid (23%)
177
When are lecithins removed in the processing of oil? Why?
- Removed from degumming
| - To use their emulsifying power for other means
178
What are the unsaponifiables contained in soybean oil? When are they removed?
- Partially removed in deodorization
