Food Biotechnology
Dr. Kamal E. M. Elkahlout
Food Biochemistry 2
Lipids
Lipids: Fats & Oils
Characteristics of Lipids
• Lipids are composed of C, H, O
– long hydrocarbon chain
fat
• Do not form polymers
– big molecules made of smaller subunits
– not a continuing chain
Fats store energy
Why do humans
like fatty foods?
• Long HC chain
– polar or non-polar?
– hydrophilic or hydrophobic?
• Function:
– energy storage
• very rich
• 2x carbohydrates
– cushion organs
– insulates body
• think whale blubber!
Classification
Many ways of classifying lipids:
Structural characteristics
• Neutral fats – found in subcutaneous tissue and around organs
• Phospholipids – chief component of cell membranes
• Steroids – cholesterol, bile salts, vitamin D, sex hormones, and
adrenal cortical hormones
• Fat-soluble vitamins – vitamins A, E, and K
• Eicosanoids – DHA (docosahexaenoic acid), EPA
(eicosapentaenoic acid) (sources of omega 3,6 & 9)
• Waxes
Fatty Acids
•
•
•
•
Long-chain carboxylic acids
Insoluble in water
Typically 12-18 carbon atoms (even number)
Some contain double bonds
corn oil contains 86%
unsaturated fatty acids and
14%
saturated fatty acids
6
Fatty Acid Structure
•Carboxyl group (COOH) forms the acid.
•“R” group is a hydrocarbon chain.
Fatty Acids
• The Length of the Carbon Chain
– long-chain, medium-chain, short-chain
• The Degree of Unsaturation
– saturated, unsaturated, monounsaturated,
polyunsaturated
• The Location of Double Bonds
– omega-3 fatty acid, omega-6 fatty acid
The Length of the Carbon Chain
Short-chain Fatty Acid
(less than 6 carbons)
Medium-chain Fatty Acid
(6-10 carbons)
Long-chain Fatty Acid
(12 or more carbons)
Unsaturated
Fatty Acid
Saturated
Fatty Acid
Saturated and Unsaturated Fatty
Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
COOH
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid
11
Properties of Saturated
Fatty Acids
• Contain only single C–C bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature
12
Properties of Unsaturated
Fatty Acids
• Contain one or more double C=C bonds
• Nonlinear chains do not allow molecules to
pack closely
• Few interactions between chains
• Low melting points
• Liquids at room temperature
13
Structures
Saturated fatty acids
• Fit closely in regular pattern
COOH
COOH
COOH
Unsaturated fatty acids
• Cis double bonds
H
H
C C
cis double bond
COOH
14
Fatty Acids are Key Building
Blocks
• Saturated Fatty Acid
• All single bonds between carbons
Monounsaturated Fatty Acid
(MUFA)
One carbon-carbon double bond
Polyunsaturated Fatty Acid
(PUFA)
More than one carbon-carbon double bond
Location of Double Bonds
• PUFA are identified by position of the
double bond nearest the methyl end (CH3)
of the carbon chain; this is described as a
omega number;
• If PUFA has first double bond :
– 3 carbons away from the methyl end=omega 3
FA
– 6 carbons from methyl end=omega 6 FA
Omega-3
Omega-6
Degree of Unsaturation
• Firmness
– saturated vs. unsaturated
• Stability
– oxidation, antioxidants
• Hydrogenation
– advantages, disadvantages
• Trans-Fatty Acids
– from hydrogenation
Cis and Trans fats
– isomerisation of cis to
trans occurs under extreme
conditions of
hydrogenation
– double bonds in fatty acids
are almost always cis,
which causes bends in the
carbon chain.
– these bends do not allow
the close packing and
attractions of saturated
fatty acids. Therefore,
most unsaturated fatty
acids are liquid at room
temperature.
Cis-9-octadecenoic acid
(Oleic acid)
Trans-9-octadecenoic acid
(Elaidic acid)
Hydrogenation Process
• liquid hardens by
hydrogenation (addition
of hydrogen)
– reduce the degree of
unsaturation
• briefly, oils are exposed
to hydrogen gas at high
tempt (2-10 atm, 160-220
0C) in the presence of
0.01-0.2% fine divided
nicklel
Saturated vs. unsaturated
saturated
unsaturated
CLASSIFICATION OF FATTY ACIDS PRESENT
AS GLYCERIDES IN FOOD FATS
Common
Name
Systematic
Name
Formula
Common source
I. Saturated Fatty Acids
Butyric
Butanoic
CH3(CH2)2COOH
butterfat
Caproic
Hexanoic
CH3(CH2)4COOH
Caprylic
Octanoic
CH3(CH2)6COOH
Capric
Decanoic
CH3(CH2)8COOH
Lauric
Dodecanoic
CH3(CH2)10COOH
Myristic
Tetradecanoic CH3(CH2)12COOH
Palmitic
Hexadecanoic CH3(CH2)14COOH
Stearic
Octadecanoic
CH3(CH2)16COOH
Arachidic
Eicosanoic
CH3(CH2)18COOH
butterfat, coconut
and palm nut oils
coconut and palm
nut oils, butterfat
coconut and palm
nut oils, butterfat
coconut and palm
nut oils, butterfat
coconut and Palm nut oil, most
animal and plant fats
practically all animal and
plant fats
animal fats and minor
component of plant fats
peanut oil
Common
Name
Systematic
Name
Formula
Common source
II. Unsaturated Fatty Acids
A. Monoethenoic Acids
Oleic
Cis 9-octadecenoic
C17H33COOH
plant and animal fats
Elaidic
Trans 9-Octadecenoic
C17H33COOH
animal fats
C17H31COOH
peanut, linseed, and
cottonseed oils
C17H29COOH
linseed and other seed
oils
peanut seed fats
B. Diethenoic Acids
Linoleic
9,12-Octadecadienoic
C. Triethenoid Acids
Linolenic
9,12,15-Octadecatrienoic
Eleostearic 9,11,13-Octadecatrienoic
C17H29COOH
D. Tetraethenoid Acids
Moroctic
Arachidonic
4,8,12,15Octadecatetraenoic
5,8,11,14-
C17H27COOH
fish oils
C19H31COOH
traces in animal fats
Common and Systematic Names of Fatty Acids
Common
Name
Systematic
Name
Formula
Common source
A. Monoethenoic Acids
Oleic
Cis 9-octadecenoic
C17H33COOH
plant and animal fats
Elaidic
Trans 9-Octadecenoic
C17H33COOH
animal fats
C17H31COOH
peanut, linseed, and
cottonseed oils
C17H29COOH
linseed and other seed
oils
peanut seed fats
B. Diethenoic Acids
Linoleic
9,12-Octadecadienoic
C. Triethenoid Acids
Linolenic
9,12,15-Octadecatrienoic
Eleostearic 9,11,13-Octadecatrienoic
C17H29COOH
D. Tetraethenoid Acids
Moroctic
Arachidonic
4,8,12,15Octadecatetraenoic
5,8,11,14Eicosatetraenoic
C17H27COOH
fish oils
C19H31COOH
traces in animal fats
CHARACTERISTICS OF FATTY ACIDS
Fatty Acids
M.P.(0C)
mg/100 ml Soluble in H2O
C4
-8
-
C6
-4
970
C8
16
75
C10
31
6
C12
44
0.55
C14
54
0.18
C16
63
0.08
C18
70
0.04
Effects of Double Bonds on the Melting Points
F. A.
16:0
16:1
18:0
18:1
18:2
18:3
20:0
20:4
M. P. (0C)
60
1
63
16
-5
-11
75
-50
Lipid Formation
Glycerol
Fatty Acid
GLYCERIDES
H2 C
O
O C
HC
OHO
H2 C
O C
H2 C OH
HC OH O
H2 C O C (CH 2 )16 CH 3
Monoglyceridea
(CH2 )16 CH3
(CH2 )16 CH3
Diglyceride
O
H2 C
HC
H2 C
O C
O
O C
O
(CH2 )16 CH3
( C18 )
(CH2 )14 CH3
(C16 )
O C
(CH2 )16 CH3
(C18 )
Triglyceride
Triglycerides
• Structure
– Glycerol + 3 fatty acids
• Functions
– Energy source
• 9 kcals per gram
• Form of stored energy in adipose
tissue
– Insulation and protection
– Carrier of fat-soluble vitamins
– Sensory properties in food
FAT AND OILS
Mostly Triglycerides:
Triglycerides
• Food sources
– fats and oils
• butter, margarine, meat, baked goods, snack
foods, salad dressings, dairy products, nuts,
seeds
– Sources of omega-3 fatty acids
• Soybean, canola, walnut, flaxseed oils
• Salmon, tuna, mackerel
– Sources of omega-6 fatty acids
• Vegetable oils
MELTING POINTS OF TRIGLYCERIDES
Triglyceride
Melting Point (°C)
C6
-15
C12
15
C14
33
C16
45
C18
55
C18:1 (cis)
-32
C18:1 (trans)
15
Learning Check
How would the melting point of stearic acid
compare to the melting points of oleic acid and
linoleic acid? Assign the melting points of –
17°C, 13°C, and 69°C to the correct fatty
acid. Explain.
stearic acid (18 C) saturated
oleic acid (18 C) one double bond
linoleic acid (18 C) two double bonds
36
Phospholipids
• Structure
– Glycerol + 2 fatty acids + phosphate
group
• Functions
–
–
–
–
Component of cell membranes
Lipid transport as part of lipoproteins
Emulsifiers
Phosphatidylcholine
• Food sources
– Egg yolks, liver, soybeans, peanuts
Phospholipids
• Hydrophobic or hydrophilic?
– fatty acid tails = hydrophobic
– PO4 = hydrophilic head
– dual “personality”
It likes water
& also pushes
it away!
interaction with H2O is
complex & very
important!
A Phospholipid
Steroids
• ex: cholesterol, sex hormones
• 4 fused C rings
– different steroids created by attaching different
functional groups to rings
cholesterol
Sterols: Cholesterol
• Functions
– Component of cell membranes
– Precursor to other substances
• Sterol hormones
• Vitamin D
• Bile acids
• Synthesis
– Made mainly in the liver
• Food sources
– Found only in animal foods
WAXES
Fatty acids + Long chain alcohol
Important in fruits:
1. Natural protective layer in fruits, vegetables, etc.
2. Added in some cases for appearance and protection.
Beeswax (myricyl palmitate)
FAT SOLUBLE VITAMINS (A,D,E,K)
Vitamin A:
H3 C
CH3
CH3
5
8
9
CH3
CH3
7
6
4
3
CH2 OH
2
1
Vitamin D2:
Vitamin E:
Deterioration of Fats
Rancidity
• Is the chemical deterioration of fats
• Are of two types
– Oxidative rancidity
– Hydrolytic rancidity
Oxidative rancidity
•
A hydrogen on the fatty acid molecule is displaced by energy(heat or light) to give
free radical.
•
Molecular oxygen can unite with the carbon that carries the free radical and form a
peroxide.
•
The energy from this activated peroxide can displace a hydrogen from another
unsaturated fatty acid.
•
The displaced hydrogen unites with the activated peroxide to form a hydroxide.
•
The hydro-peroxide is very unstable and can decompose into compounds with
shorter carbon chains. These include ketones, aldehydes and fatty acids that are
volatile and contribute to off flavoures.
Oxidative Rancidity
Catalysts
–
–
–
–
Salt and trace metals
Bacteria and molds
Water
Light
Prevention
• Addition of chelators
• Use of antioxidants
• Air tight storage.
Hydrolytic Rancidity
• Is the reaction between a triglyceride and 3 water
molecule to give a glycerol and 3 free fatty acids.
Catalysts :
• Heat
• Fat splitting enzymes called lipases.
Prevention
• Keep moisture level low
• Inert gas packaging
• sterilization
Functional Properties of Lipids
•
•
•
•
•
•
•
Flavour
Basting – add crispiness to product
Add moisture to foods
Assist in browning
Frying
Aerating
Prevents products from sticking