Transcript fats2

Fats
– simple glycerol based lipids
– compound glycerol based lipids
– non-glycerol based lipids
Crude fat
(Soxhlet extraction, 8 hours, petroleum ether or
hexane; all the fat soluble substances of the food)
– simple lipids (triacylglycerols, fats – oils)
Compound glycerol based lipids
– Phosphoglycerides
glycerol + fatty acid + phosphoric acid + cholin = lecithin,
glycerol + fatty acid + ethanolamine = cephalins
lecithin
–Glycolipids
glycerol + fatty acids + simple sugars (glucose,
galactose etc.)
The lipids of grasses contain 50-60% glycolipids,
mostly galactolipids. 95% of the fatty acids is
linolenic acid.
Non-glycerol based lipids
•Vaxes
• long chain fatty acid + long chain alcohol
• hydrophobic nature, reducing water loss
• resistant to breakdown, poorly utilised
•Steroids (biologically active compounds)
• cholesterol (present in all animal cells, constituent of cell
membranes, precursor of steroid hormones, and bile acids)
• 7-dehydrocholesterol  vitamin D3 precursor (animals)
• ergosterol  vitamin D2 precursor (plants, bacteria, algae)
• bile acids
• steroid hormones (oestrogens, androgens, progesterone,
cortisol, aldosteron, corticosteron)
•Terpenes
• odour and flavour materials,
• essential oils
• carotenoids,
• vitamins A, E and K
steroid hormones
Nutritional role of fats
• Energy supplementation of diets
• Quality of animal products (fat content, fatty acid
composition)
• fat soluble vitamins
• Essential fatty acids
– linoleic acid C18:2
– α – linolenic acid C18:3
– Arachidonic acid C20:4
• flavour compounds
• helps in pelleting
• carnivores > poultry > pig > ruminants
Common fatty acids of natural fats and oils
Acid
Formula
Melting point
Fatty acid composition of some common fats and oils
CIS OR TRANS FATTY ACIDS
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These terms refer to the arrangement of hydrogen atoms
in unsaturated fatty acids.
Nearly all 'natural' fats contain cis fatty acids. Trans fatty
acids, although unsaturated, behave in the body like
saturated fatty acids.
They are present in some animal fats and dairy products
and are formed during processing in margarine.
The amounts vary, being between 1-7% in butter fat but
up to 35% in some margarines.
Omega-3 or n-3 and omega-6 or n-6 fatty acids
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These are terms which describe the position of double
bonds within the fatty acid molecule.
These types of fatty acids are advantageous nutritionally.
Linoleic acid, an essential fatty acid, which is present in
vegetable oils is an n-6 acid.
N-3 fatty acids, present in vegetables and fish oils lower
plasma triglycerides and have anti-clotting and antiinflammatory properties.
α – linolenic acid is a representative of the n-3 group.
DIGESTION OF FATS
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Over 90% of the fat eaten is absorbed from the gut.
Bile is produced by the liver.
The surface of fats is enormously increased by the production of
a very fine emulsion in the small intestine.
Fat is broken down by the pancreatic enzyme lipase to glycerol,
fatty acids and monoglycerides.
Mixed micelles are formed.
In the cells lining the small intestine, these digestive products are
resynthesized into fat,
Fats are incorporated into a shell of water-soluble protein, and
enter the bloodstream as chylomicrons.
These particles contain cholesterol as well as being rich in
triglycerides.
Digestion and absorption of lipids
The digestibility of fatty acids depends on
the length and saturation of fatty acids
steraic acid
• Length of the chain
– the digestion of shorter
chain fatty acids is
better
oleic acid
• Saturation
– absorption rate of
unsaturated fatty acids
is higher
linoleic acid
METABOLISM AND TRANSPORT OF FATS
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Lipids are insoluble in water and cannot be carried in
solution in the plasma.
The combination of lipids with proteins is called lipoprotein.
Lipoproteins found in the blood are classified according to
their density.
CLASSIFICATION OF LIPOPROTEINS
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Very low density lipoprotein (VLDL) - mainly triglyceride
Intermediate density lipoprotein (IDL) - triglyceride/cholesterol
Low density lipoprotein (LDL) - mainly cholesterol
High density lipoprotein (HDL) - phospholipid/cholesterol and the
smallest
Chylomicrons-mainly triglyceride, and much the largest particle
After a meal containing fat,
• chylomicrons enter the blood.
• adipose tissue and skeletal muscle contain an enzyme (lipoprotein
lipase) which breaks down the fat in the chylomicrons to fatty acids
and glycerol.
• these products are then used by the cells for energy or stored as fat.
Between meals,
• the liver secretes VLDL which supply the tissues with triglycerides.
• The remnants left from VLDL form IDL and then LDL.
• LDL is cholesterol-rich, accounting for about 70% of the plasma
cholesterol.
• It is a risk factor for CHD and has been shown to be the source of
cholesterol in atheroma.
• If, there is more LDL in the blood than needed by the cells, it enters
macrophages (white blood cells) but in an unregulated fashion.
• These LDL-packed cells then become 'foam cells' and, deposited
within the arterial wall, begin the development of atherosclerosis.
Oxidation of fats
• Hydrolysis
– production of free fatty acids
– not toxic, but reduced palatability
• Oxidation
– it happens at the double bonds
– hydropeoxides and ketones are produced
– high temperature, ultraviolet light and some metal ions catalyse the
reaction
– free radicals react with other fatty acids, cell membranes, sensitive
vitamins (vitamin A, D, E), carotenoids
• Antioxidants
– Natural:
• tocopherols (vitamin E)
• ascorbic acid
– Artificial: BHA (butilated hidroxyanisol)
BHT (butilated hidroxytoluen)
EMQ (etoxi metilquinone)
Relative amounts of products
Some parameters related to the quality of fats
Nb of peroxides
Nb of free fatty acids
NbNb
ofof
polymers
polymers
Nb of aldehydes
time
Dioxin concentration of several foods
(pg/g fat)
fish oil
beef
pork
chicken
lamb
horse
goat
rabbit
milk
10,0
1,8
0,43
1,7
1,9
14,0
4,2
20,0
1,5
mother milk
cheese
egg
see fish
freshwater fish
eel
mussel
salmon
herring
34,0
1,4
2,0
45,0
2,4
28,0
79,0
16,0
46,0
Fatty acid composition of cell membrane
phospholipid in different populations (%)
Europe/USA
Arachidonic acid (n-6)
26
Eikosapentaenoic acid (n-3) 0,5
n-6:n-3 fatty acid ratio
50
cardiovascular mortality
45
Japan Eskimo
21
8,3
1,6
8,0
12
1
1
7
Modification the fatty acid profile of
chicken meat
• olive oil
• corn, soybean,
sunflower oil
• linseed oil
• fish oil
oleic acid (Yau et al., 1991)
linoleic acid (Scaife et al., 1990)
linolenic acid (Manilla, 1999)
EPA, DHA (Ratnayake et al., 1989)
• n-3 long chain fatty acids incorporate mostly into the
phospholipid fraction of muscle tissues
• There is a difference among muscles (more into the
breast meat compared to tight)
Meats containing higher amount of
polyunsaturated fatty acids, needs protection
against oxidation
• Feeding diets with increased vitamin E
(275 IU/kg) for 3 weeks before slaughter
increased the muscle vitamin E content
of turkey from 1,6 mg/kg to 5 mg/kg
(Sheldon, 1984).
• With broilers 100 IU/kg of vitamin E
also increased the vitamin E content to
the desirable level (7 mg/kg) (Lin et al.,
1980)
n-3 fatty acid enrichment foods
No. 1. = fish
Other meats (pork, poultry)
Egg
Milk and milk products
Health risks related to fatty acid composition
CORONARY HEART DISEASE
• Coronary heart disease (CHD) is the narrowing of the lumen of the
coronary arteries by atheroma, a deposit which contains cholesterol. The
atheroma may then be the site of a blood clot, causing further narrowing
and reduction in blood supply.
• CHD is a multifactorial disease and a number of risk factors have been
identified, prominent among them being raised blood cholesterol.
• The level of blood cholesterol is influenced by a number of factors and one
of them is the percentage of dietary energy from saturated fats.
CANCERS
• Some cancers are associated with a high fat intake.
• The mortality from colon cancer in a population is proportional to its
saturated fat intake;
• The mortality from rectal cancer is proportional to the prevailing P/S ratio.
BREAST CANCER
• Breast cancer mortality for a population is roughly proportional to total fat
intake.
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People with familial hypercholesterolaemia have few LDL
receptors.
The blood LDL and, therefore, cholesterol level is very
high and the risk of premature CHD very great.
HDL transports excess tissue cholesterol to the liver.
HDL seems to be protective against CHD.
The blood lipids which are commonly measured are:
optimal level
total serum cholesterol (fasting)
5.2-5.7 mmol/litre
LDL cholesterol
3.5-4.0 mmol/litre
total triglyceride
<2.3 mmol/litre
Dietary fat affects blood lipids and blood clotting in the
following ways:
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total plasma cholesterol and LDL are raised by saturated fatty acids,
carbon length 12 to 16 (present in dairy products, coconut oil, meat
fat) and trans fatty acids (mainly margarine);
cholesterol (highest in offal, egg yolk, mayonnaise and shell-fish) may
raise total blood cholesterol but this effect is very variable and less
important than that caused by fatty acids;
total plasma cholesterol and LDL are lowered by PUFA of the ω-6
series;
long-chain PUFA of the ω-3 series (fish oils) lower plasma
triglycerides, and have anti-clotting and anti-inflammatory properties.
These facts, derived from epidemiological and experimental underlie the
recommendations for requirement values.