Fish Lipids

Lipids

Lipids (generally soluble in organic solvents Plant sources (olive, palm) No cholesterol

Animal sources (butter, lard, tallow)

Oils and Fats Triacylglycerol Sterols

Waxes (monoesters)

Lipids Definition of Lipids 

Naturally occurring biological substances made from C, H and O of pronounced hydrophobicity that are soluble in organic solvents but not water    

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Petroleum distillates (e.g. hexane) Chloroform Ethers Alcohols

Also classified as “biological molecules containing fatty acids or the corresponding alcohols or sphingosine bases” Lipids have more C and H than carbohydrates, which is why they generate more energy when utilized  2.25 times more = 9 kcal/g vs. 4 kcal/g.

Lipids Biological role A. Structural - found in membranes - protective barriers B. Regulatory - steroids/prostaglandins - phospholipids C. Storage - triglyceride is storage for energy D. Vitamins - solvent - precursor

Lipids Role in foods A. Calories (kcal) – energy <30% of all calories (ideal) - satiety B. Essential fatty acids - linoleic acid, linolenic acid arachadonic acid C. Flavor - most lipid soluble (usually offflavors) D. Texture – mouth feel & appearance E. Color - carotenoids F. Heat transfer medium

v.s.

v.s.

Lipids Classification of lipids (structure) 1) Simple lipids  

Mono, Di and Triacylglycerols Waxes

Glycerol backbone

Fatty acids

2) Compound lipids   

Phospholipids Glycolipids Sphingolipids (amide to alcohol)

3) Derived lipids    

Free fatty acids Sterol esters Tocopherol (Vit-E) β-carotene

Triacylglycerol

Lipids Classifications of lipids (polarity) 1) Non-polar lipids (neutral lipids)      

Fatty acids Mono-, di-, & triacylglycerols Waxes Sterols Carotenoids Tocopherols

2) Polar lipids    

Glycerophospholipid Glyceroglycolipid Sphingophospholipid Sphingoglycolipid

Lipids Structure & properties of fatty acids 

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Fatty acid are composed of a hydrocarbon chain with methyl group (CH3) on one end and a carboxyl group (COOH) on the other. Basic properties common to most fatty acids 1. Most are even carbon # 2. Most are monocarboxylic acids 3. Most are part of triacylglycerides (triglycerides)

Lipids NOMENCLATURE 1. Number of carbons  

C4-C24 most common E.g. C8 = octa C12 = dodeca

2. Saturation 

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Saturated (no double bonds) Unsaturated (double bonds)  

Mono (1 = bond) Poly (>1 = bond)

Lipids 2. Saturation (cont.) 

No double bond = Anoic 

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One double bond = Enoic 

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E.g. C18:1

Two double bonds = Dienoic 

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E.g. C18:0

E.g. C18:2

Three double bonds = Trienoic 

E.g. C18:3

3. Geometric configuration of double bonds  

Cis vs. Trans Has an influence on the fatty acid backbone structure

Lipids 4. Position of double bonds 

Delta (Δ) system - count # of carbons to the = bond from the COOH end  

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E.g. Δ 9-octadecenoic acid Means: a) C18 = octadecenoic b) 1 double bond = octadecenoic c) double bond is 9 carbons from the COOH end

Omega (ω) system - count # of carbons to the = bond from the CH3 end – used for abbreviations of fatty acids 

E.g. Δ 9-octadecenoic acid would be C18:1ω9 ω-3 therefore would mean that the = bond is 3 C from the CH3 end

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ω-3, ω-6 and ω-9 the most common

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Lipids What is the name of this fatty acid using the delta & omega systems? H3C-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH

Delta: ___________________________ Omega: __________________________ Common name is Linoleic acid (C18:2)

Lipids Major fatty acids in foods  Saturated  

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Monoenoic 

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Linoleic (18:2ω6) – Δ9, 12 - common in plants; some in animal

Trienoic 

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Oleic (18:1ω9)

Dienoic 

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Palmitic (16:0) Stearic (18:0)

Linolenic (18:3ω3) Δ9, 12, 15

Tetraenoic 

Arachadonic (20:4ω6) - Δ 5, 8, 11, 14 - part of membrane phospholipids

Lipids Factors affecting the properties of fatty acids 1.Length of fatty acids 

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Longer chain length leads to increase in melting point and gives more stable fat crystals Classes: 

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C4 – C8 - liquid @ room temperature (20-25°)  These are water soluble  good emulsifiers C10 - C14 - viscous @ room temperature C16 - C26 - solid @ room temperature

For example:   

C6:0  MP = -2°C C10:0  MP = 31.5°C C16:0 MP = 63°C

Lipids Factors affecting the properties of fatty acids 2. Double bonds 

An increase in double bonds decreases melting point Example: 18:0 = 70°C 18:1 = 15°C 18:2 = -5°C 18:3 = -11°C

Lipids Factors affecting the properties of fatty acids 3. Cis vs. Trans 

Cis has lower melting point than Trans 

Cis produces a kink in the fatty acid chain which creates a more open fatty crystal structure

Melting Point Kink

18:1c 18:1t

15°C 44 °C

18:2c 18:2t

-5 °C 29 °C

18:3c 18:3t

-11 °C 71 °C

Lipids Arrangement of fatty acids on triacylglycerides 1. Not random (usually) 2. Specificity controlled 3. General pattern

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Position

Plant

Mammal

Milk

Bird

Fish

1

S

S

S

S

S-LC

2

U

U

S

U

U

3

U

LC

U or SC

S or U

LC

The arrangement can significantly affect physical properties of fat LC : Long chain; SC: Short chain

Lipids Importance of sn position; Cocoa butter vs. Tallow

High mp

Low mp

Cocoa Butter

Tallow

% 16:1

62.00

64.00

Consistency

hard sharp mp

greasy broad mp

SSS

0.03

0.28

SSU

0.01

0.16

SUS

0.81

0.32

SUU

0.15

0.18

USU

0.01

0.02

UUS

0.01

0.03

Lipids Important Compound Lipids 1. Phospholipids   

Make up cellular membranes Lipid molecules that contain a phosphate group attached to a functional group Have both hydrophobic (fatty acids) and hydrophilic (phosphate and functional group) portions 

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Good emulsifiers

May have a protective effect against ulcers (milk PL)

Lipids 2. Glycolipids 

Contain at a minimum one sugar 

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Some may also have a phosphate group (glycosphingolipids)

Found in all tissues of animals Have same solubility characteristics as regular lipids

3. Sterols  

Made of four fused hydrophobic rings with a hydrophilic OH group Not so important as a food ingredient but important for dietary reasons  

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Cholesterol in animal foods Can contribute to coronary heart disease (arteriosclerosis) 300 mg/day the recommended intake limit

Lipids 4. Fat substitutes  Sucrose fatty acid polyesters 

Olestra ® (Procter and Gamble Co.)  

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6-8 fatty acids (>C12) esterified to sucrose Caloric free due to its bulky structure and because lipases cannot hydrolyze it May lead to loss of fat soluble vitamins and can give diarrhea Approved for use in frying oils (snacks)

Sucrose and polyol fatty acid esters   

1-3 fatty acids esterified to sucrose or a polyol (e.g. sorbitol) Have caloric value (polyol fatty acid esters only about 1.5 kcal/g) Used as emulsifiers and stabilizers

Triacylglycerol

Sterols

Wax (bees wax)

Simple lipids Monoglyceride

Diglyceride

Triglyceride

Compound Lipids

Phosphate group

Sugar unit

Phospholipid Glycolipid

Derived Lipids

Sterols

Carotene

 Peptide based liquid  Tube or oral feeding  Efficient energy utilization

 MCT OIL (Novartis nutrition)  unable to digest or absorb conventional fats  Less enzymes and bile acids for digestion

Fish Lipids  

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Fish are classified as lean, semi-fatty or fatty. Fish that store lipids only in the liver as lean and fish storing lipids in fat cells distributed in other body tissues as fatty. Typical lean species are bottom-dwelling ground fish like cod, and hake. Fatty species include pelagic such as herring, mackerel and sprat. Some species store lipids in limited parts of their body tissues only, or in lower quantities than typical fatty species, and are consequently termed semi- fatty species (e.g. barracuda, mullet and shark).

Type of lipids in fish 

The lipids present in teleost fish species may be divided into two major groups: 

Phospholipids 

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Triglycerides 

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The phospholipids make up the integral structure of the unit membranes in the cells; thus, they are often called structural lipids. The triglycerides are lipids used for energy storage in fat depots, usually within special fat cells surrounded by a phospholipid membrane and a rather weak collagen network.

The triglycerides are often termed depot fat. A few fish have wax esters as part of their depot fats.

Fish & Mammals lipids 

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Fish and mammalian lipids differ mainly in that fish lipids include up to 40 percent of long-chain fatty acids (14-22 carbon atoms) which are highly unsaturated. Mammalian fat rarely contains more than two double bonds per fatty acid molecule while the depot fats of fish contain several fatty acids with five or six double bonds.

Lipids: marine & freshwater fish 

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The percentage of polyunsaturated fatty acids with four, five or six double bonds is slightly lower in the polyunsaturated fatty acids of lipids from freshwater fish (approximately 70 percent) Lipids from marine fish (approximately 88 percent). 

However, the composition of the lipids is not completely fixed but can vary with the feed intake and season

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