Lipid Flashcards

(59 cards)

1
Q

oleic acid [c-x or t-x nomenclature]

A

18:1 c-9

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2
Q

elaidic acid [c-x or t-x nomenclature]

A

18:1 t-9

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3
Q

Linoleic acid [c-x or t-x nomenclature]

A

18:2 c-9, c- 12

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4
Q

stearic acid [c-x or t-x nomenclature]

A

18:0

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5
Q

α -linolenic acid [c-x or t-x nomenclature]

A

18: 3

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6
Q

lipids

A

Substances of biological origin that have the common properties:

  • soluble in non-polar solvents
  • poorly soluble in water
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7
Q

Lipid classification

A

Simple lipids / Complex lipids / Derived lipids

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8
Q

Derived lipids

A

non-hydrolysable, e.g. free fatty acids, sterols, tocopherol, vitamin A, etc

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9
Q

Complex lipids

A

yield 3 or more classes on hydrolysis, e.g. phospholipids are esters of alcohols, fatty acids and phosphoric acid

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10
Q

Simple lipids

A

yield 2 classes of product on hydrolysis, e.g. glycerides (acylglycerols) are esters of glycerol and fatty acids

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11
Q

14:0

A

myristic acid

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12
Q

palmitic acid

A

16:0

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13
Q

4:0

A

butyric acid

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14
Q

lauric acid

A

12:0

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15
Q

Notable PUFAs

A

alpha- Linolenic acid (18:3 c-9, c-12, c-15)

gemma- Linolenic acid (18:3 c-6, c-9, c-12)

Arachidonic acid (20:4 c-5, c-8, c-11, c-14)

Eicosapentaenoic acid (20:5 c-5,c-8,c-11,c-14,c-17)

Docosahexaenoic acid (22:6 c-4,c-7,c-10,c-13,c-16, c-19)

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16
Q

Extraction of oils and fats

A

Mechanical pressing / Solvent extraction/ Rendering

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17
Q

Rendering

A

extraction of animal fats by combined action of water and heat

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18
Q

Solvent extraction

A

e.g. rapeseed oil

Seeds or nuts with higher oil content cannot be fully extracted by mechanical pressing

Petroleum ether or hexane can be used to further recover residual oil from pressed cake

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19
Q

Mechanical pressing

A

e.g. olive oil

De-shelled/de-hulled and coarsely ground plant material is heated and pressed in hydraulic or screw presses

Use no heating for cold-pressed or virgin oil

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20
Q

Olive oil

A

Several grades available: Virgin olive oil is highest quality

> obtained by pressing the fruit by mechanical means under conditions where no change in the oil occur

> only washing, decanting, centrifuging, filtration allowed

> further classified by flavour and free acidity

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21
Q

Virgin olive oil Characteristics

A
  • pale green colour
  • good flavour
  • good stability: rich in phenolic antioxidants (secoiridoids) and low in linoleic acid (18:2)
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22
Q

Virgin olive oil Nutrition

A
  • diets rich in oleic acid (18:1 c-9) lead to low LDL cholesterol levels without reducing HDL cholesterol
  • antioxidants may be beneficial
  • 100 mg/kg α-tocopherol
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23
Q

Palm oil

A
  • Palm fruit also used as raw material for biodiesel fuel (600 USD per ton)
  • Tocopherol content 170 mg/kg
  • Tocotrienol content 570 mg/kg
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24
Q

Palm kernel oil

A
  • Tocopherol content 3 mg/kg
  • Commonly fractionated into palm kernel olein and palm kernel stearin
  • Palm kernel stearin used in chocolate flavoured coatings
25
Soybean oil
- Soybeans major crop of USA, Argentina, Brazil - Oil is extracted with hexane; soybean meal is good source of protein for animal feeds - Soy lecithin is good commercial source of phospholipids - Vitamin E 1500 mg/kg
26
Rapeseed oil
Production 14 million tons in 2002-3 Produced from double-low rapeseed - low in glucosinolates, which allows meal to be used for animal feed - low in erucic acid (22:1), which allows oil to be used as human food
27
Refining of edible oils
Neutralisation / Bleaching / Deodorisation / Antioxidant / Degumming
28
Neutralisation
to remove free fatty acids (cause soapy/rancid off-flavours; smoke on heating)
29
Bleaching
to remove pigments (stir with bleaching earth; adsorption removes soaps, oxidation products, some metal ions)
30
Deodorisation
To remove off-odours (heat with steam under vacuum at 200 - 240°C)
31
Antioxidant
may add primary antioxidants, e.g. BHA (butylated hydroxyanisole) or metal-chelating agents, e.g. citric acid
32
Degumming
- to remove phospholipids and polysaccharides (gums) | - add hot water or phosphoric acid or citric acid
33
edible oils should avoid
- carry-through of metal ions (which catalyse oxidation) - foaming in deodoriser - losses into aqueous phase - black specks on heating
34
Requirements for fat in foods
- Correct texture > Correct melting range > Crystal form/stability (in the case of solid fats) - Suitable crystallisation rate for processing (solid fats) - Acceptable flavour and flavour stability - Good price
35
Factors that influence a higher melting points in fatty acid
- Higher number of carbon atoms - Lower number of carbon-carbon double bonds - Trans rather than cis C=C - Straight chain rather than branched fatty acids
36
Factors that influence a higher melting points in Triacylglycerols
- Asymmetric vs. symmetric: PPO > POP - Polymorphism (crystalline structure): β (beta) > β’ (beta prime) > α (alpha) most stable least stable slow cooling rapid cooling
37
Polymorphism
the occurrence of several different crystal forms for the same compound
38
Fat Bloom
the appearance of rough and/or white crystals on surface > caused by uncontrolled recrystallization of triglycerides into an undesirable crystal form > melting and migration of triglycerides can occur during storage
39
Packing of polymorphs in solid state
α - hexagonal 90* β’ - orthorhombic 68-70* β - triclinic 59*
40
Polymorphism in chocolate
Tempering > avoids bloom and good contraction from moulds > allows fat to crystallise into form V (polymorph β) (with higher melting point)
41
Tempering Plain chocolate:
- melt at 50°C > cool in scraped surface heat exchanger (tempering unit) to 27 - 28°C (1-2% fat crystallises into mixture of α and β' crystals) > heat to 30-32°C to melt β' crystals (0.1-1.0% solid remains) > fill mould or use for enrobing > cool product in cooling tunnel at 0-15°C - β crystals grow on existing crystal surfaces
42
Polymorphism in margarine
In order to have a glossy surface, the fat in margarine should be stable in the β’ form ``` Some fats (e.g. palm oil) convert to α crystals on storage this causes large fat crystals to grow, and the surface becomes dull (graininess or sandiness) ``` Avoid graininess by selecting suitable fat blends, especially interesterified fats
43
Modification of edible fats
Hydrogenation / Transesterification / Fractionation / Blending
44
Blending
mixing 2 or more fats changes the melting range and composition Blending of a semi-solid fat with a liquid oil will generally lead to a softening of the product Unexpected softening or hardening effects may occur when blending two fats if eutectic or compound phase behaviour is observed
45
Fractionation
physical separation Dry fractionation/ Solvent fractionation
46
Transesterification or interesterification
chemical reaction or lipase-catalysed transesterification > Stir fat (or fat blend) with sodium methoxide or sodium at 90°C > Random rearrangement of fatty acids between triacylglycerol molecules to produce a fat with a wide melting range, which is stable in the β’ polymorph
47
Hydrogenation
chemical reaction Produces a semi-solid fat from a liquid oil > raises melting point of triacylglycerols > improves flavour stability Only partial hydrogenation used
48
Solvent fractionation
- most efficient > dissolve semi-solid fat in warm solvent > stir as reduce temperature until fat crystals appear filter off fat crystals from liquid oil solution > evaporate solvent
49
Dry fractionation
> semi-solid fat stirred at moderate temperature after melting > separate higher melting fat and liquid oil
50
The liquid fraction is called | The solid fraction is called
The liquid fraction is called the olein fraction The solid fraction is called the stearin fraction
51
Hydrogenation conditions
neutralised, bleached oil stirred with hydrogen at 150-180°C, 1-6 bar, nickel catalyst (0.1-0.5%), stirring (1000 rpm)
52
Side reaction of Hydrogenation
isomerisation > increased melting point > loss of nutritional quality double bond migration > change of ratio of PUFA
53
Oleic acid
cis unsaturated fatty acid making up 55–80% of olive oil
54
Elaidic acid
trans unsaturated fatty acid side reaction product found in partially hydrogenated vegetable oils
55
Stearic acid
intended product, saturated fatty acid found in animal fats
56
Nutritional effects of trans unsaturated fatty acids
Increase: 1. total plasma cholesterol 2. LDL cholesterol 3. HDL cholesterol 4. lipoprotein a Effects 1 & 2 similar to saturated fatty acids Effects 3 & 4 are undesirable
57
Mechanism of hydrogenation
- Hydrogenation occurs at the surface of the nickel catalyst, where hydrogen, and unsaturated fatty acids (in triacylgycerols) are bound > Increase hydrogen supply to catalyst surface (increased H pressure; faster stirring) to favour addition of hydrogen
58
Effect of conditions on hydrogenation selectivity
Conditions that favour addition of H cause: - increased consumption of linoleic and linolenic acids in TAGs - increased formation of saturated fatty acids (with less monounsaturates) - reduction of trans formation Increase hydrogen demand at metal surface* - increased linoleic acid selectivity, i.e. 18:2 reduced to 18:1 with less 18:0 formed - increased trans formation
59
Advantages and disadvantages of fat modification techniques
Blending + cheap and normally produces products with properties in between those of 2 fats Interesterification + chemical reaction but nutritional quality more or less same as blend of fats Fractionation - physical separation of triacylglycerols Hydrogenation - formation of trans fatty acids, loss of PUFA + can use a wide range of raw materials, e.g. fish oil