Lipids I Flashcards
What are lipids soluble in? Give examples.
- Non-polar solvents
- Hexane, chloroform, ether
What are the three major classes of lipids?
- Simple lipids
- Compound lipids
- Derived lipids
What are simple lipids?
Esters of fatty acids connected to an alcohol
What are the two types of simple lipids?
- Fats
- Waxes
What are compound lipids?
Simple lipid (generally of the triglyceride type) conjugated to a non-lipid molecule
What are derived lipids?
Constituents that are derived from the simple or compound lipid categories and still retain their hydrophobic character
What are the three types of compound lipids?
- Phospholipids
- Glycolipids and sphingolipids
- Lipoproteins
What are the three types of derived lipids?
- Fatty acids
- Alcohols
- Other diverse hydrocarbons
Differentiate fats and waxes.
Fats: esters of fatty acids connected to glycerol
Waxes: esters of fatty acids esterified with an alcohol, other than glycerol
What are fatty acids?
Short-to-long chain aliphatic hydrocarbons with a carboxyl group at one end
Differentiate oils and fats.
- Oil: low melting point; liquid at room temperature
- Fat: high melting point; solid at room temperature
Triglycerides account for ____% of the extractible lipid material present
> 90%
Differentiate the melting point of pure triglycerides and edible fats. Why are they different?
- Pure triglyceride: sharp melting point
- Edible fats: melt over a wider range of temperature because it consists of a mixture of different pure triglyceride molecules
How would you isolate fast melting fats?
- Fractionation
- Take olive oil, put it in the refrigerator overnight
- One component is fast melting (liquid); the other component is solid
Is solid or liquid fat better for frying? Why?
Solid is better because there are more saturated fats
What is the difference in terms of structure between liquid and solid waxes? Give examples of both.
Liquid wax: short-chain (ex: jojoba oil)
Solid wax: long-chain
What is a true wax?
Fatty acid esterified to a simple fatty alcohol
How are waxes used in the food industry?
- Sealing agents (cheese)
- Polishing agents (apples)
- Potential low-calorie food ingredient
Name some other compounds in the wax category.
- Fatty acids esterified to a complex alcohol (ex: cholesterol)
- Esters of vitamin A or retinol
- Vitamin A ester
Why are waxes important even if they aren’t often present in a food system?
Important because they are biologically active
What is the general structure of phospholipids?
- Triglycerides with one of their fatty acids replaced with a non-lipid moiety = phosphoric acid
- Phosphoric acid is commonly conjugated to some other non-lipid moiety
In phospholipids, what is “X” usually?
A nitrogenous base
In phospholipids, what is the structure called when X=OH?
Phosphatidic acid
In phospholipids, what is the structure called when X=O-CH2-CH2-NH2?
Phosphatidylethanolamine
In phospholipids, what is the structure called when X=O-CH2-CH2-N+(CH2)3
Phosphatidylcholine
In phospholipids, what is the structure called when X=O-CH2-CH(NH2)-COOH
Phosphatidylserine
In phospholipids, what is the structure called when X=sugar
Phosphatidylinositol
What are the three classes of phospholipids?
- Lecithins (Phosphatidylcholines)
- Cephalins (Phosphatidylethanolamines)
- Phosphatidyl inositols
What is the common name for phosphatidylcholines?
Lecithins
What is the common name for phosphatidylethanolamines?
Cephalins
What are phosphatidyl inositols?
- Non-nitrogenous group attached to phosphatic acid
- Phosphate group esterified with inositol
Why are phospholipids great emulsifiers?
Contain both hydrophobic and hydrophilic domains
Phospholipids comprise ____% of the lipid material found in food systems.
<5%
When we refer to “phospholipids” in general, what are we referring to?
Usually a complex mixture of these constituents without defining their exact chemical structure
What kind of compounds are more likely to be soluble in ethanol?
Charged
Which compound lipids have little consequence to the food scientist? (2)
- Glycolipids
- Sphingolipids
What are sphingolipids? What role do they share with glycolipids?
- Combination of glycerol-like backbone (sphingosine), fatty acids, carbohydrate, and/or a nitrogenous group
- Associated with membrane lipids in both plants and animals
What are lipoproteins? What does the center contain? What does it carry on the outside?
- Protein-lipid complexes, which circulate in blood to carry lipids to tissues for metabolism or storage
- Contains triacylglycerols and cholesterol esters in the center
- Apolipoproteins, cholesterol, and phospholipids on the outside
Which of the lipoproteins is more dense? Which contains more fat?
- HDL is more dense (good)
- LDL contains more fat (bad)
How can LDL be harmful?
- When there is an excess of LDL or when it undergoes structural changes, LDL can accumulate in blood vessels
- This can lead to blockages in arteries or unstable plaque build-up
How can HDL be healthful?
Serves as a protective mechanism from the development of heart disease by carrying away cholesterol from vessel walls and plaque to the liver for disposal
How do short-chain fatty acids and long-chain fatty acids differ in terms of their contributions to flavour?
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
How are short-chain fatty acids released?
Lipolysis
Give examples of short-chain fatty acids that contribute to flavour.
- Butyric acid (C4)
- Caproic acid (C6)
- Caprylic acid (C8): cheese flavour/rancidity
The presence of ________ can lower the smoke point of edible oils when used for frying.
free fatty acids
What does this structure correspond to?
CH3-(CH2)n-CH2-OH
How many carbons do they need to have at least?
- Alcohols
- At least 6 carbons
Short-chain ______ are often major contributors to flavour.
alcohols
More complex derived alcohols are often ____________________. For example, ________________.
- biologically active
- cholesterol
What do other diverse hydrocarbons refer to?
- Short-and-long-chain aliphatic hydrocarbons
- Carotenoids
- Xanthophylls
- Terpenes
What does this structure correspond to?
CH3-(CH2)n-CH3
Other diverse hydrocarbons
Do straight-chain saturated hydrocarbons contribute to flavour?
Do not contribute much to flavour or reactions
Which diverse unsaturated hydrocarbon is particularly interesting? What is it made of?
- Terpenes
- Made of isoprene units
How many carbons does a fundamental isoprene unit contain?
5 carbons
What are terpenes components of?
Components of the fragrant oils obtained from leaves, flowers and fruits
What are the main constituents of essential oils?
Monoterpenes, with sesquiterpenes
How many isoprene units and carbons do these terpene classes contain: A) Monoterpenes B) Sesquiterpenes C) Diterpenes D) Sesterterpenes E) Triterpenes
A) 2, 10 B) 3, 15 C) 4, 20 D) 5, 25 E) 6, 30
Lipid storage in storage tissues can rise to _____% and serve as a commercial source for isolation of triacylglycerols.
15-20%
Which lipids are present in foods the most? (2)
- Triglycerides (95%)
- Phospholipids (5%)
Are essential oils, oleoresins, waxes, carotenoids, and short-chain oxidation products considered fats and oils from a practical standpoint?
No
A broad distribution of fatty acids gives you a broad _________.
melting range
Which fatty acid is the simplest and least reactive?
Saturated
Are fatty acids found in nature even or odd numbered?
- Even
- Odd numbers are present in food only in traces
Compare the structure of saturated and unsaturated fatty acids.
- Saturated: linear, saturated with carbons, no double bonds
- Unsaturated: kinks, one or more double bonds
How do the melting points of shorter-chain fatty acids differ from longer-chain fatty acids?
Short-chain (C4-C8): liquid at room temp; lower melting point
Long-chain (>C10): solid at room temp; higher melting point
Water solubility decreases with increasing FA chain length due to?
Increasing hydrophobicity
Which fatty acids are slightly miscible in water?
C4-C8
What form of a fatty acid is water soluble and has strong surface tension reducing properties?
Salt form of a fatty acid (soap)
Liquid: P+
Solid: Na+
What is the function of fatty acids with an odd number of carbons?
Important as food aroma constituents
What are the most common unsaturated fatty acids? How many double bonds do they contain? Where?
- Oleic: 1 (9)
- Linoleic acid: 2 (9, 12)
- Linolenic acid: 3 (9, 12, 15)
What are the two major systems of nomenclature? Which one tends to predominate?
- Trivial names: predominate
- Systematic names (IUPAC)
What are the two levels that are introduced with systematic naming of unsaturated fatty acids?
- Positional
- Structural (cis and trans) isomers
The presence of a double bond is indicated by the suffix _____
“enoic”
In the IUPAC system, the position of the double bond is counted from which end?
From the CARBOXYL end of the FA chain
Differentiate cis and trans. How do their shapes differ?
Cis: hydrogens are on the same side of the carbon chain (U shape)
Trans: hydrogens next to the double bond are on opposite sides of the carbon chain (linear)
Are fatty acids usually found in cis or trans?
Cis
Conversion of double bonds from cis to trans has a major effect on what? What is this process called?
- Effect on the melting point of the fat
- Hydrogenation
What does the pentadiene system state?
- Penta for 5
- Diene for 2 double bonds
- In nature, double bonds are interrupted by a methyl group
Is rotation possible after hydrogenation?
Yes
Does trans has a higher melting point than saturated?
No, saturated > trans > cis
What is the main mechanism for oils becoming plastic fats?
cis -> trans conversion during hydrogenation
Butter naturally contains substantial levels of trans fatty acids. How?
Due to hydrogenation of cis fatty acids to trans by rumen microorganisms
What is positional isomerism? What does it affect?
- Where the double bond is located on the fatty acid chain
- Affect the physical properties of mono-unsaturated fats but is a less significant variable than
cis/trans configuration
Differentiate unconjugated and conjugated double bonds.
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)
Are unconjugated or conjugated double bonds more stable? Which one is more susceptible to autoxidation?
Thermodynamically speaking, the conjugated form is more stable but is more susceptible to autoxidation
In linolenic and higher polyunsaturated fatty acids, the double bonds are all _____________. What is it readily converted to?
unconjugated
- Relatively reactive, unstable
- Readily converted to a mixed bonding system
What is a mixed bonding system?
Having both conjugated/unconjugated elements
What does a mixed bonding system lead to? Where is that positioned?
- Leads to formation of an ACTIVE METHYLENE group
- Positioned between a conjugated and unconjugated double bonds
Which system is preferred thermodynamically but is very susceptible to autoxidation? What is it responsible for?
- Mixed bonding system
- Largely responsible for the REVERSION phenomenon associated with soybean and fish oils
Where do you start counting for omega fatty acids?
Start counting from the CH3 end
The omega nomenclature is based on two assumptions. What are they?
- All natural fatty acids are in the cis form
- The double bonds will be always be unconjugated
Natural linoleic acid has _ unconjugated double bonds, the first between the __th and __th carbon from the omega end, the second between the __th and __th
- 2 unconjugated double bonds
- First: 6th and 7th
- Second: 9th and 10th
Arachidonic acid, C__, with __ unconjugated double bonds, the first double bond in position _, the next at _, _, and _, respectively
- C20
- 4 unconjugated double bonds
- 6, 9, 12, 15
What group does Erucic acid belong to?
Omega-9
What group does arachidonic acid belong to?
Omega-6
What groups do linolenic, linoleic, and oleic acid belong to?
w3 (linolenic type),
w6 (linoleic type) and
w9 (oleic acid type)
Which fatty acid is only synthesized by plants?
Omega-3
What are conjugated linoleic acids found in? Why are they important? What is their structure?
- Found in milk and meat
- Attributed to have an anticarcinogenic effect.
- Various C18 fatty acids with two double bonds which differ in position and geometry belong to the group CLA. The most common is the cis- 9, trans-11 isomer.
Where are you most likely to find DHA and EPA?
Fish oils
Are double bonds or the length of the carbon chain more important in determining the melting point?
Double bonds
Can the position of a double bond affect the melting point?
Yes, especially if it is in the middle, it can lower the melting point
The cis-configuration in oleic acid causes a bending of about ___°
40o
The extent of molecular crumpling is also increased by an increase in the number of ___ double bonds. Thus, the four cis double bonds in arachidonic acid increase the deviation from a straight line to ___°.
cis, 165o
What is the crystalline lattice stabilized by?
Hydrophobic interaction along the acyl residues
The energy (temperature) required to melt the crystal increase with an ________ number of carbons in the chain.
increased
What can be uniformly packed into a crystalline lattice? What can’t?
Can: saturated and even-numbered acids
Can’t: odd-numbered and unsaturated fatty acids
What is the molecular arrangement in the crystalline lattice of unsaturated fatty acids strongly influenced by? What isn’t it strongly influenced by?
Influenced: cis double bonds
Not influenced: trans double bonds
The melting point ________ with an increasing number of isolated cis-double bonds
decreases
Where do cis double bonds cause the least deviation?
When a cis double bond is at the end of the carbon chain
What are branched-chain fatty acids?
Have a hydrocarbon branch in the chain
What causes egg colour problems in chicken eggs (pasty and rubbery yolks)? What kind of fatty acid is it
- Malvalic acid (found in cottonseed oil)
- Branched-chain fatty acid
Microorganisms often contain a wide variety of ________ chain fatty acids
branched
What are hydroxy acids? What are they present in?
- Contain a hydroxyl group in the fatty acid chain
- Present in oil of the castor bean tree
What are cyclic fatty acids?
Contain a cyclic group in the chain
What are acetylenic fatty acids? What are they useful for?
- Contain a triple bond
- Useful as antifungals
Are saturated or unsaturated fatty acids more reactive?
Saturated: relatively unreactive
Unsaturated: more reactive
