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2) Food Chemistry I > Lipids I > Flashcards

Lipids I Flashcards

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1
Q

What are lipids soluble in? Give examples.

A
  • Non-polar solvents

- Hexane, chloroform, ether

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2
Q

What are the three major classes of lipids?

A
  • Simple lipids
  • Compound lipids
  • Derived lipids
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3
Q

What are simple lipids?

A

Esters of fatty acids connected to an alcohol

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4
Q

What are the two types of simple lipids?

A
  • Fats

- Waxes

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5
Q

What are compound lipids?

A

Simple lipid (generally of the triglyceride type) conjugated to a non-lipid molecule

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6
Q

What are derived lipids?

A

Constituents that are derived from the simple or compound lipid categories and still retain their hydrophobic character

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7
Q

What are the three types of compound lipids?

A
  • Phospholipids
  • Glycolipids and sphingolipids
  • Lipoproteins
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8
Q

What are the three types of derived lipids?

A
  • Fatty acids
  • Alcohols
  • Other diverse hydrocarbons
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9
Q

Differentiate fats and waxes.

A

Fats: esters of fatty acids connected to glycerol
Waxes: esters of fatty acids esterified with an alcohol, other than glycerol

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10
Q

What are fatty acids?

A

Short-to-long chain aliphatic hydrocarbons with a carboxyl group at one end

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11
Q

Differentiate oils and fats.

A
  • Oil: low melting point; liquid at room temperature

- Fat: high melting point; solid at room temperature

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12
Q

Triglycerides account for ____% of the extractible lipid material present

A

> 90%

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13
Q

Differentiate the melting point of pure triglycerides and edible fats. Why are they different?

A
  • 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
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14
Q

How would you isolate fast melting fats?

A
  • Fractionation
  • Take olive oil, put it in the refrigerator overnight
  • One component is fast melting (liquid); the other component is solid
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15
Q

Is solid or liquid fat better for frying? Why?

A

Solid is better because there are more saturated fats

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16
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

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17
Q

What is a true wax?

A

Fatty acid esterified to a simple fatty alcohol

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18
Q

How are waxes used in the food industry?

A
  • Sealing agents (cheese)
  • Polishing agents (apples)
  • Potential low-calorie food ingredient
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19
Q

Name some other compounds in the wax category.

A
  • Fatty acids esterified to a complex alcohol (ex: cholesterol)
  • Esters of vitamin A or retinol
  • Vitamin A ester
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20
Q

Why are waxes important even if they aren’t often present in a food system?

A

Important because they are biologically active

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21
Q

What is the general structure of phospholipids?

A
  • 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
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22
Q

In phospholipids, what is “X” usually?

A

A nitrogenous base

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23
Q

In phospholipids, what is the structure called when X=OH?

A

Phosphatidic acid

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24
Q

In phospholipids, what is the structure called when X=O-CH2-CH2-NH2?

A

Phosphatidylethanolamine

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25
Q

In phospholipids, what is the structure called when X=O-CH2-CH2-N+(CH2)3

A

Phosphatidylcholine

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26
Q

In phospholipids, what is the structure called when X=O-CH2-CH(NH2)-COOH

A

Phosphatidylserine

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27
Q

In phospholipids, what is the structure called when X=sugar

A

Phosphatidylinositol

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28
Q

What are the three classes of phospholipids?

A
  • Lecithins (Phosphatidylcholines)
  • Cephalins (Phosphatidylethanolamines)
  • Phosphatidyl inositols
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29
Q

What is the common name for phosphatidylcholines?

A

Lecithins

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30
Q

What is the common name for phosphatidylethanolamines?

A

Cephalins

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31
Q

What are phosphatidyl inositols?

A
  • Non-nitrogenous group attached to phosphatic acid

- Phosphate group esterified with inositol

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32
Q

Why are phospholipids great emulsifiers?

A

Contain both hydrophobic and hydrophilic domains

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33
Q

Phospholipids comprise ____% of the lipid material found in food systems.

A

<5%

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34
Q

When we refer to “phospholipids” in general, what are we referring to?

A

Usually a complex mixture of these constituents without defining their exact chemical structure

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35
Q

What kind of compounds are more likely to be soluble in ethanol?

A

Charged

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36
Q

Which compound lipids have little consequence to the food scientist? (2)

A
  • Glycolipids

- Sphingolipids

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37
Q

What are sphingolipids? What role do they share with glycolipids?

A
  • Combination of glycerol-like backbone (sphingosine), fatty acids, carbohydrate, and/or a nitrogenous group
  • Associated with membrane lipids in both plants and animals
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38
Q

What are lipoproteins? What does the center contain? What does it carry on the outside?

A
  • 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
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39
Q

Which of the lipoproteins is more dense? Which contains more fat?

A
  • HDL is more dense (good)

- LDL contains more fat (bad)

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40
Q

How can LDL be harmful?

A
  • 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
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41
Q

How can HDL be healthful?

A

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

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42
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

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43
Q

How are short-chain fatty acids released?

A

Lipolysis

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44
Q

Give examples of short-chain fatty acids that contribute to flavour.

A
  • Butyric acid (C4)
  • Caproic acid (C6)
  • Caprylic acid (C8): cheese flavour/rancidity
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45
Q

The presence of ________ can lower the smoke point of edible oils when used for frying.

A

free fatty acids

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46
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

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47
Q

Short-chain ______ are often major contributors to flavour.

A

alcohols

48
Q

More complex derived alcohols are often ____________________. For example, ________________.

A
  • biologically active

- cholesterol

49
Q

What do other diverse hydrocarbons refer to?

A
  • Short-and-long-chain aliphatic hydrocarbons
  • Carotenoids
  • Xanthophylls
  • Terpenes
50
Q

What does this structure correspond to?

CH3-(CH2)n-CH3

A

Other diverse hydrocarbons

51
Q

Do straight-chain saturated hydrocarbons contribute to flavour?

A

Do not contribute much to flavour or reactions

52
Q

Which diverse unsaturated hydrocarbon is particularly interesting? What is it made of?

A
  • Terpenes

- Made of isoprene units

53
Q

How many carbons does a fundamental isoprene unit contain?

A

5 carbons

54
Q

What are terpenes components of?

A

Components of the fragrant oils obtained from leaves, flowers and fruits

55
Q

What are the main constituents of essential oils?

A

Monoterpenes, with sesquiterpenes

56
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
57
Q

Lipid storage in storage tissues can rise to _____% and serve as a commercial source for isolation of triacylglycerols.

A

15-20%

58
Q

Which lipids are present in foods the most? (2)

A
  • Triglycerides (95%)

- Phospholipids (5%)

59
Q

Are essential oils, oleoresins, waxes, carotenoids, and short-chain oxidation products considered fats and oils from a practical standpoint?

A

No

60
Q

A broad distribution of fatty acids gives you a broad _________.

A

melting range

61
Q

Which fatty acid is the simplest and least reactive?

A

Saturated

62
Q

Are fatty acids found in nature even or odd numbered?

A
  • Even

- Odd numbers are present in food only in traces

63
Q

Compare the structure of saturated and unsaturated fatty acids.

A
  • Saturated: linear, saturated with carbons, no double bonds

- Unsaturated: kinks, one or more double bonds

64
Q

How do the melting points of shorter-chain fatty acids differ from longer-chain fatty acids?

A

Short-chain (C4-C8): liquid at room temp; lower melting point
Long-chain (>C10): solid at room temp; higher melting point

65
Q

Water solubility decreases with increasing FA chain length due to?

A

Increasing hydrophobicity

66
Q

Which fatty acids are slightly miscible in water?

A

C4-C8

67
Q

What form of a fatty acid is water soluble and has strong surface tension reducing properties?

A

Salt form of a fatty acid (soap)
Liquid: P+
Solid: Na+

68
Q

What is the function of fatty acids with an odd number of carbons?

A

Important as food aroma constituents

69
Q

What are the most common unsaturated fatty acids? How many double bonds do they contain? Where?

A
  • Oleic: 1 (9)
  • Linoleic acid: 2 (9, 12)
  • Linolenic acid: 3 (9, 12, 15)
70
Q

What are the two major systems of nomenclature? Which one tends to predominate?

A
  • Trivial names: predominate

- Systematic names (IUPAC)

71
Q

What are the two levels that are introduced with systematic naming of unsaturated fatty acids?

A
  • Positional

- Structural (cis and trans) isomers

72
Q

The presence of a double bond is indicated by the suffix _____

A

“enoic”

73
Q

In the IUPAC system, the position of the double bond is counted from which end?

A

From the CARBOXYL end of the FA chain

74
Q

Differentiate cis and trans. How do their shapes differ?

A

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)

75
Q

Are fatty acids usually found in cis or trans?

A

Cis

76
Q

Conversion of double bonds from cis to trans has a major effect on what? What is this process called?

A
  • Effect on the melting point of the fat

- Hydrogenation

77
Q

What does the pentadiene system state?

A
  • Penta for 5
  • Diene for 2 double bonds
  • In nature, double bonds are interrupted by a methyl group
78
Q

Is rotation possible after hydrogenation?

A

Yes

79
Q

Does trans has a higher melting point than saturated?

A

No, saturated > trans > cis

80
Q

What is the main mechanism for oils becoming plastic fats?

A

cis -> trans conversion during hydrogenation

81
Q

Butter naturally contains substantial levels of trans fatty acids. How?

A

Due to hydrogenation of cis fatty acids to trans by rumen microorganisms

82
Q

What is positional isomerism? What does it affect?

A
  • 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
83
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)

84
Q

Are unconjugated or conjugated double bonds more stable? Which one is more susceptible to autoxidation?

A

Thermodynamically speaking, the conjugated form is more stable but is more susceptible to autoxidation

85
Q

In linolenic and higher polyunsaturated fatty acids, the double bonds are all _____________. What is it readily converted to?

A

unconjugated

  • Relatively reactive, unstable
  • Readily converted to a mixed bonding system
86
Q

What is a mixed bonding system?

A

Having both conjugated/unconjugated elements

87
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

88
Q

Which system is preferred thermodynamically but is very susceptible to autoxidation? What is it responsible for?

A
  • Mixed bonding system

- Largely responsible for the REVERSION phenomenon associated with soybean and fish oils

89
Q

Where do you start counting for omega fatty acids?

A

Start counting from the CH3 end

90
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

91
Q

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

A
  • 2 unconjugated double bonds
  • First: 6th and 7th
  • Second: 9th and 10th
92
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
93
Q

What group does Erucic acid belong to?

A

Omega-9

94
Q

What group does arachidonic acid belong to?

A

Omega-6

95
Q

What groups do linolenic, linoleic, and oleic acid belong to?

A

w3 (linolenic type),
w6 (linoleic type) and
w9 (oleic acid type)

96
Q

Which fatty acid is only synthesized by plants?

A

Omega-3

97
Q

What are conjugated linoleic acids found in? Why are they important? What is their structure?

A
  • 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.
98
Q

Where are you most likely to find DHA and EPA?

A

Fish oils

99
Q

Are double bonds or the length of the carbon chain more important in determining the melting point?

A

Double bonds

100
Q

Can the position of a double bond affect the melting point?

A

Yes, especially if it is in the middle, it can lower the melting point

101
Q

The cis-configuration in oleic acid causes a bending of about ___°

A

40o

102
Q

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 ___°.

A

cis, 165o

103
Q

What is the crystalline lattice stabilized by?

A

Hydrophobic interaction along the acyl residues

104
Q

The energy (temperature) required to melt the crystal increase with an ________ number of carbons in the chain.

A

increased

105
Q

What can be uniformly packed into a crystalline lattice? What can’t?

A

Can: saturated and even-numbered acids

Can’t: odd-numbered and unsaturated fatty acids

106
Q

What is the molecular arrangement in the crystalline lattice of unsaturated fatty acids strongly influenced by? What isn’t it strongly influenced by?

A

Influenced: cis double bonds

Not influenced: trans double bonds

107
Q

The melting point ________ with an increasing number of isolated cis-double bonds

A

decreases

108
Q

Where do cis double bonds cause the least deviation?

A

When a cis double bond is at the end of the carbon chain

109
Q

What are branched-chain fatty acids?

A

Have a hydrocarbon branch in the chain

110
Q

What causes egg colour problems in chicken eggs (pasty and rubbery yolks)? What kind of fatty acid is it

A
  • Malvalic acid (found in cottonseed oil)

- Branched-chain fatty acid

111
Q

Microorganisms often contain a wide variety of ________ chain fatty acids

A

branched

112
Q

What are hydroxy acids? What are they present in?

A
  • Contain a hydroxyl group in the fatty acid chain

- Present in oil of the castor bean tree

113
Q

What are cyclic fatty acids?

A

Contain a cyclic group in the chain

114
Q

What are acetylenic fatty acids? What are they useful for?

A
  • Contain a triple bond

- Useful as antifungals

115
Q

Are saturated or unsaturated fatty acids more reactive?

A

Saturated: relatively unreactive
Unsaturated: more reactive

2) Food Chemistry I (31 decks)

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