Lipids - Summary Flashcards
What are the three groups of lipids?
- Simple lipids
- Compound lipids
- Derived lipids
What are the two groups of simple lipids?
- Triglycerides
- Waxes
What are the three groups of compound lipids?
- Phospholipids
- Glycolipids
- Lipoproteins
What is jojoba oil?
An ester (simple lipid)
Why does an edible fat melt over a much wider range than a pure triglyceride?
Because it consists of many different pure TG molecules, each with different melting points
What are waxes?
Esters of fatty acids esterified with an alcohol, other than glycerol
Give examples of compounds in the wax category.
- Cholesterol
- Esters of vitamin A
When X is OH, what is the phospholipid called?
Phosphatidic acid
When X is O-CH2-CH(NH2)-COOH, what is the phospholipid called?
Phosphatidylserine
When X is a sugar, what is the phospholipid called?
Phosphatidylinositol
When X is O-CH2-CH2-N+(CH2)3, what is the phospholipid called?
Phosphatidylcholine (lecithin)
When X is O-CH2-CH2-NH2, what is the phospholipid called?
Phosphatidylethanolamine (cephalin)
What is the fundamental unit of terpenes? How many carbons does it contain?
Isoprenes (5 carbons)
How many isoprene units and carbons do monoterpenes contain?
2 isoprene units, 10 carbons
Name the terpene classes in chronological order.
- Monoterpenes
- Sesquiterpenes
- Diterpenes
- Sesterterpenes
- Triterpenes
What chain length of fatty acids are slightly miscible with water?
C4-C8
What is the systematic name of myristic acid?
Tetradecanoic acid (14:0)
What is the systematic name of stearic acid?
Octadecanoic acid (18:0)
What is the systematic name of palmitic acid?
Hexadecanoid acid (16:0)
What are the names for 18:1, 18:2, and 18:3 fatty acids?
- Oleic
- Linoleic
- Linolenic
Give the systematic names of fatty acids from C2 to C22 (even-numbers only).
- Ethanoic (C2)
- Butanoic (C4)
- Hexanoic (C6)
- Octanoic (C8)
- Decanoic (C10)
- Dodecanoic (C12)
- Tetradecanoic (C14)
- Hexadecanoic (C16)
- Octadecanoic (C18)
- Eicosannoic (C20)
What are C2:0, C4:0, and C12:0 fatty acids?
- C2:0 - acetic
- C4:0 - butyric
- C12:0 - lauric
How do you indicate the presence of a double bond in nomenclature?
By the suffix “enoic”
What are unconjugated double bonds?
Separated by a methylene group (natural state)
What is a conjugated double bond?
Double bonds are next to each other (more susceptible to autoxidation)
Which fatty acid is readily converted to a mixed bonding system? What does that lead to?
- Linolenic acid
- Formation of an active methylene group, positioned between a conjugated and unconjugated double bonds
- Very susceptible to autoxidation
What is largely responsible for reversion in soybean and fish oils?
The active methylene group of linolenic acid
Where do you start counting in Omega-nomenclature? What does 10:23 mean?
- Methyl end
- 10 carbons with two double bonds, the first positioned at 3 from the methyl end
What is 20:46?
Arachidonic acid
What are the distinguishing features of the milkfat group?
- High levels of long-chain saturated fatty acids
- Unique and substantial portion of short-chain fatty acids (ex: butyric acid)
What is responsible for the “rancid like” odor from lipolysis in milkfats?
Short-chain fatty acids
What are sources of the lauric acid group?
- Palm kernal oil (extracted from oilseed)
- Coconut
- Tropical oils
What is palm oil?
- Extracted from palm FRUIT
- Much more unsaturated, not a lauric acid
What is the distinguishing feature of the lauric acid group?
- High content of lauric acid (C12:0)
- Mostly saturated
Why are lauric acids oils at room temperatures?
Despite their saturation, they are oils due to lauric acids short-chain (C12)
Which group is resistant to oxidative rancidity?
Lauric acid, due to their low degree of unsaturation
Give examples of the oleic-linoleic acid group.
- Cottonseed
- Olive
- Peanut
- Corn
Why don’t oleic-linoleic group fatty acids suffer from reversion?
Negligible amount of linolenic fatty acids
Give examples of linolenic acids.
Soybean, hempseed
Which group’s fatty acids are qualified as drying oils?
- Linolenic acids
- Because of their ability to polymerize into a hard film if applied as a thin layer
Why are animal fat depot group fats rather than oils?
- Despite their high content of unsaturated fatty acids,
- They are fats because they have a higher ratio of GS2 (disaturated) and GS3 (trisaturated) glycerides
What is the distinguishing feature of marine oils?
- High in long-chain unsaturated fatty acids (C16-C22)
- Very highly unsaturated (up to 6 double bonds)
- High in omega-3 fatty acids
- REVERSION and autoxidation
Give examples of erucic fatty acids.
- Rapeseed oil
- Mustard oil
What is erucic acid?
- C22:1
- Health hazard
What is canola oil?
Low erucic acid edible oil
Corn oil, safflower oil, and sunflower oil are examples of what?
Omega-6 fatty acids
Olive oil, avocados, peanuts, and almonds are examples of what?
Omega-9 fatty acids
What does lipase catalyze?
- Lipolysis
- Hydrolysis of the ester linkage between glycerol and a fatty acid in a TG
What does lipoxygenase catalyze?
- The oxidation of polyunsaturated fatty acid chains that have a cis-cis-1,4-pentadiene group
What are the three ways to obtain oil from a plant source? How are they different?
- Hydraulic pressing: poor quality, long time, more enzyme damage
- Expelling: press cake still contains oil, followed by solvent
- Solvent extraction: organic solvent (hexane), efficient
What are the four steps to the refinement of oil?
1) Settling and degumming
2) Refining
3) Bleaching
4) Deodorization
What does settling and degumming extract? How?
- Mixing the oil with water and allowing it to stand
- Carbohydrates, proteins, and phospholipids dissociate (aqueous)
What does refining extract? How?
- Treatment with dilute alkali, to convert FAs into soap
- Removal of free fatty acids from the oil
What does bleaching extract? How?
- Oil is passed through dry bentonite or clay
- Removal of coloured material from the oil
What does deodorization extract? How?
- Steam stripping
- Removal of volatile compounds
What is biodiesel?
Methyl esters
How can fatty acid composition/distribution be determined?
Gas chromatography
What is winterization? What was it developed with?
- Cooling down the oil to remove saturates
- Cottonseed oil
What are the functions of hydrogenation? (2)
- Convert an oil into a fat
- Reduce the susceptibility of an oil to oxidative rancidity
What are the double bonds formed by hydrogenation capable of? What does that result in?
- Wandering (positional isomerism)
- Conversion of unconjugated double bonds to mixed bonding systems
What is selectivity?
Hydrogenation prefers highly unsaturated fatty acids
Why is interesterification used in lard?
- GS2U component is made of oleopalmitostearin, which has a propensity to form large crystals
- Interesterification solves that problem
What are the two ways to determine the solid fat content?
- Dilatometry
- Nuclear magnetic resonance (NMR)
What is plotted in a dilatometry graph?
Specific volume, inverse of density (y) as a function of temperature (x)
What do the three sigmoidal represent in dilatometry?
1) Thermal expansion of the solid fat
2) Expansion due to a change in state
3) Thermal expansion of the ilquid only
What is the equation of the solid fat index?
- (X/Y) x 100
- X is the measurement between the curve and the liquid line
- Y is the measurement between the liquid line and the solid line
Which polymorphic form has the highest and lowest melting point?
- Highest: beta
- Lowest: alpha
What polymorphic form arises from the rapid cooling of liquid fat?
Alpha
What polymorphic form arises from the slow cooling of liquid fat?
Beta
Beta-Prime is the polymorphic transformation of what?
Alpha
Coconut, corn, and olive oil prefer the _____ crystal form
beta
Cottonseed, milk fat, and palm oil prefer the ______ crystal form
beta-prime
What are the four methods for conversion from beta to beta-prime?
- Interesterification
- Interesterification and hydrogenation
- Winterization
- Addition of cottonseed oil and/or tallow flakes
Differentiate interesterification and intraesterification.
- Interesterification: exchange among TG molecules
- Intraesterification: exchange WITHIN a TG molecule
What are high temperature base catalysts for interesterification? What is the low-temperature catalyst?
- High: KOH and NaOH
- Low: NaOCH3 (sodium methoxide)
What are the three steps to interesterification?
1) Formation of enolate ion
2) Formation of B-keto ester
3) Interesterification
What is the definition of catalyst activity?
Decrease in iodine number per unit of time during a hydrogenation under a specific set of conditions
What is the iodine number? What does it indicate?
- The number of grams of iodine absorbed by 100 grams of fat
- Indicates the degree of unsaturation of the fatty acid
What are the independent variables affecting the reaction rate of hydrogenation?
- Nature of the substance
- Concentration of the catalyst
- Pressure
- Temperature
- Agitation
What are the dependant variables affecting the reaction rate of hydrogenation?
- trans fatty acids
- Selectivity ratio
- Hydrogenation rate
How does an increase in temperature affect the selectivity ratio, trans content, and reaction rate in hydrogenation?
Selectivity ratio: increases
Trans content: increases
Reaction rate: increases
How does an increase pressure affect the selectivity ratio, trans content, and reaction rate in hydrogenation?
Selectivity ratio: decreases
Trans content: decreases
Reaction rate: increases
How does an increase in agitation affect the selectivity ratio, trans content, and reaction rate in hydrogenation?
Selectivity ratio: decreases
Trans content: decreases
Reaction rate: increases
How does an increase in catalyst affect the selectivity ratio, trans content, and reaction rate in hydrogenation?
Selectivity ratio: increases
Trans content: increases
Reaction rate: increases
What is saponification?
Hydrolysis of an ester under alkaline conditions
How do you use gas chromatography?
1) Saponify
2) Chromatograph methyl esters
3) Determine peak areas
What are the two methods to obtain the iodine value?
- Wijis
- Hanus
What is cocoa butter composed of?
- 80% is DISATURATED
- SOS, POS, POP
What determines the characteristic cocoa butter texture?
POS
What happens when POS in cocoa butter is transformed from the beta-prime form to the beta form?
Chocolate “bloom” - white spots and dull surface appearance
What is tempering?
Process which permits transformation to the proper polymorphic form
What is reduced in the random interesterification of lard?
Proportion of palmitic acid in the 2-position is reduced –> improves its plastic range
What is autoxidation? What is the overall result?
- Reaction of unsaturated FAs with molecular oxygen
- Development of rancidity
What does autoxidation require?
1) Hydrogen must be abstracted from the FA chain
2) Molecular oxygen must be present
How can hydrogen be abstracted from the FA chain?
- Light
- Heat
- Metallic cations
- Lipoxygenase
- Singlet oxygen
What is propagation in autoxidation?
Reaction of the fatty acid free radical with oxygen
What is the key to the self-propagating nature of the autoxidation reaction? What does that form?
- The peroxy radical has a preference for terminating its free radical state by abstracting a hydrogen from another FA
- Forms a hydroperoxide and a new FA radical
What are the primary oxidation products?
- Hydroperoxides (predominate)
- Peroxides
What are the compounds responsible for off-flavors in autoxidation? What is their precursor?
- Low-molecular weight aldehydes, alcohols, ketones
- Hydroperoxide
When does the monomolecular hydroperoxide mechanism predominate?
When the hydroperoxide concentration is low
When does the bimolecular hydroperoxide mechanism predominate?
When the hydroperoxide concentration is high
What does the monomolecular reaction form?
Alkoxy and hydroxy radicals
What three reactions can an alkoxy radical undergo? Which releases a free radical?
- Aldehyde generation (radical)
- Alcohol generation (radical)
- Ketone generation (termination)
What reactions can an aldehyde undergo? (2)
- Oxidation to a carboxylic acid
- Reduction to an alcohol
What does the bimolecular reaction form?
Alkoxy and peroxy radicals + H2O
What do peroxy radicals prefer to do?
Abstract a hydrogen from a fatty acid
What do alkoxy radicals prefer to do?
Decompose –> aldehydes, ketones, alcohols, carboxylic acids
What does the peroxide value indicate? Does it accurately portray rancidity?
- Measures the quantity of hydroperoxides
- No, since hydroperoxides decrease at the end of the reaction since they are degraded, which produces the off-flavours
What is the slow accumulation of hydroperoxides called?
Induction period (primarily monomolecular reaction)
What does the TBA test indicate?
- Secondary breakdown products of autoxidation
- MALONALDEHYDE –> produces a red complex
Is citric acid an antioxidant? Why/why not?
- No, it is a chelating agent (synergistic agent)
- It does NOT interfere with primary autoxidation mechanism
What are metal ions contribution to autoxidation?
Allow for the formation of more reactive singlet oxygen, which can attack lipids directly
Give examples of synergists.
- Ascorbic acid
- EDTA
What are the detrimental effects of lipoxygenase?
1) Destruction of essential FAs
2) Free radicals produce damage
3) Development of off-flavour
Give examples of preventative antioxidants.
- Superoxide dismutase
- Catalse
- Glutathione peroxidase
- EDTA
Give examples of radical scavenging antioxidants.
- Vitamin C
- Tocopherol
- Anthocyanin
Does a hydroxy free radical have a low or high electron reduction potential?
- High (2300)
- Greater affinity for electrons, will get reduced
What should antoxidants not exceed?
200 ppm
What is an ideal antioxidant?
- No harmful physiological effects
- Effective in low concentration
- Readily-available
- Economical
- Fat-soluble
