Lipids

Question 1

chemical structure

Answer 1

a triglyceride is formed when one molecule of glycerol combines with three fatty acids
glycerol is a trihydric alcohol with three hydroxyl groups (OH)
a fatty acid (R=COOH) molecule attaches itself to each OH group with the elimination of water

Question 2

classification of fatty acids

Answer 2

saturated
monounsaturated
polyunsaturated

Question 3

saturated fatty acids

Answer 3

fully saturated with hydrogen atoms
no double bonds

solid at room temp
high melting point

sources: dairy, egg yolk
eg butyric acid in butter, stearic acid in meat

Question 4

monounsaturated fatty acids

Answer 4

carbon chain not saturated with hydrogen atoms
bonds are incomplete
one double bond

liquid/soft at room temp
lower melting point
lowers cholesterol

sources: plants
eg oleic acid in olive oil

Question 5

polyunsaturated fatty acids

Answer 5

carbon atoms not saturated with hydrogen atoms
more than 1 double bond

liquid/soft at room temp
lowest melting point
lowers cholesterol

sources: nuts, seeds, veg oil
eg linoleic acid

Question 6

what are fatty acids

Answer 6

long chains of hydrocarbons

has a methyl group (CH3) at one end and a carboxyl group (COOH) at the other end

Question 7

cis fatty acids

Answer 7

hydrogen atoms are located on the same side as a double bond, causing a bend in the chain
sources: foods containing fat or oil

Question 8

trans fatty acids

Answer 8

formed from cis when heating/frying oils at high temperatures and during industrial processing
hydrogen atoms are located at opposite sides of the double bond, molecules are rigid
sources: fried foods, hard margarine

Question 9

significance of trans fatty acids in the diet

Answer 9

1. may contribute to increased risk of CHD
2. raised levels of LDL (bad cholesterol)
3. high levels in the diet reduce HDLs

Question 10

omega 3 fatty acids

Answer 10

determined by the position of the double bond
double bond is between the third and fourth carbons
sources: oily fish, nuts, soya beans, seeds

Question 11

benefits of omega 3 fatty acids

Answer 11

help lower blood fat levels
reduce risk of blood clots, strokes, CHD
improve brain function

Question 12

functions of essential fatty acids

Answer 12

1. to build healthy cell membranes
2. to reduce risk of CHD
3. to counteract effects of cholesterol in arteries

Question 13

classification, sources and degree of saturation of lipids

Answer 13

animal- dairy, meat, meat fats - mainly saturated
plant- avocado, cereals, nuts- unsaturated except for some margarines
marine- oily fish eg mackerel, salmon, fish oils from cod - omega 3 polyunsaturated fatty acids (EPA and DHA)

Question 14

properties of hard fats and oils

Answer 14

rancidity 
hydrogenation
plasticity 
emulsions
stabilisers

Question 15

rancidity

Answer 15

spoilage of lipids by:
oxidative rancidity - oxygen in air reacts with carbon atoms in the double bond in an unsaturated chain
hydrolytic rancidity- enzymes or microbes react in a lipid, breaking it down into glycerol and fatty acid eg freezer

Question 16

hydrogenation

Answer 16

occurs when hydrogen is forced through the double bond of an unsaturated fatty acid in the presence of a nickel catalyst, converting it to a saturated fat eg margarine

Question 17

plasticity

Answer 17

whether a lipid is solid, liquid or spreadable
allows for shape and structure and is determined by the degree of saturation: the more unsaturated fatty acids present , the softer the lipid

Question 18

emulsions

Answer 18

form when two immiscible liquids are forced together to form a solution : oil in water or water in oil
permanent (emulsifier used) or temporary (shaken together)

Question 19

working principle of an emulsifier

Answer 19

the hydrophilic end (water loving) attaches itself to the water molecule.
the hydrophobic end (water hating) end attaches itself to the fat/oil molecule.
the mixture stabilises

Question 20

examples of emulsions in food

Answer 20

lecithin in mayo (oil in water)

casein in butter (water in oil)

Question 21

stabilisers

Answer 21

maintain emulsions in cakes, ice cream and salad cream, preventing ingredients separating out
eg gelatine, pectin

Question 22

biological functions of lipids

Answer 22

concentrated source of heat and energy
excess forms adipose tissue
protect delicate organs
source of fat soluble vitamins
source of essential fatty acids

Question 23

energy value

Answer 23

1g = 37 kJ

Question 24

associated dietary disorders

Answer 24

obesity 
CHD
strokes
high cholesterol
high blood pressure

Question 25

culinary functions of lipids

Answer 25

improves flavour

involved in emulsification

Question 26

digestion of lipids in liver

Answer 26

bile- bile salts- large fat globules-emulsified fats

Question 27

digestion of lipids in pancreas

Answer 27

pancreatic juice- pancreatic lipase- lipids- gly. and f acids

Question 28

digestion of lipids in small intestine

Answer 28

intestinal juice- intestinal lipase- lipids- gly. and f acids

Question 29

absorption of lipids

Answer 29

glycerol and fatty acids are absorbed into the lacteals of the villi of the small intestine
digested lipids are transported by the lymph to the bloodstream via the left subclavian vein

Question 30

utilisation of lipids

Answer 30

oxidised in the liver and muscles to produce heat and energy, and form cell membranes
excess is stored as adipose tissue or around delicate organs
energy reserve

Question 31

HDLs

Answer 31

counteract the hardening effects of cholesterol

remove cholesterol from circulation and reduce the risk of heart disease

Question 32

LDLs

Answer 32

harmful, thought to build up cholesterol in the arteries damaging blood vessels and causing heart disease

Question 33

flash point

Answer 33

lipids spontaneously burst into flames
fats - 310 degrees
oils - 325 degrees
decomposition of lipids continues

Question 34

smoke point

Answer 34

lipids begin to decompose into glycerol and fatty acids
fats - 200 degrees
oil - 250 degrees
produces an acrid smelling compound, acrolein