Fats

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Fats

• simple glycerol based lipids
• compound glycerol based lipids
• non-glycerol based lipids

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• Crude fat
• (Soxhlet extraction, 8 hours, petroleum ether or
  hexane all the fat soluble substances of the
  food)
• simple lipids (triacylglycerols, fats oils)

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• Compound glycerol based lipids
• Phosphoglycerides
• glycerol fatty acid phosphoric acid cholin
  lecithin,
• glycerol fatty acid ethanolamine cephalins

lecithin
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• 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.

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• 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

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steroid hormones
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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 C182
• a linolenic acid C183
• Arachidonic acid C204
• flavour compounds
• helps in pelleting
• carnivores gt poultry gt pig gt ruminants

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Common fatty acids of natural fats and oils
Acid Formula
Melting point
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Fatty acid composition of some common fats and
oils
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• CIS OR TRANS FATTY ACIDS
• 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.

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• Omega-3 or n-3 and omega-6 or n-6 fatty acids
• 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 anti-inflammatory properties.
• a linolenic acid is a representative of the n-3
  group.

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• DIGESTION OF FATS
• 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.

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Digestion and absorption of lipids
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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
• Saturation
• absorption rate of unsaturated fatty acids is
  higher

oleic acid
linoleic acid
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• METABOLISM AND TRANSPORT OF FATS
• 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
• 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

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• 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.

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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)

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Some parameters related to the quality of fats
Nb of peroxides
Nb of free fatty acids
Relative amounts of products
Nb of polymers
Nb of polymers
Nb of aldehydes
time
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Dioxin concentration of several foods (pg/g
fat) fish oil 10,0 mother milk
34,0 beef 1,8 cheese 1,4 pork
0,43 egg 2,0 chicken 1,7 see fish
45,0 lamb 1,9 freshwater fish
2,4 horse 14,0 eel 28,0 goat
4,2 mussel 79,0 rabbit 20,0 salmon
16,0 milk 1,5 herring 46,0
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Fatty acid composition of cell membrane
phospholipid in different populations ()
Europe/USA Japan Eskimo Arachidonic
acid (n-6) 26 21 8,3 Eikosapentaenoic
acid (n-3) 0,5 1,6 8,0 n-6n-3 fatty
acid ratio 50 12 1
cardiovascular mortality 45 1
7
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• Modification the fatty acid profile of chicken
  meat
• olive oil oleic acid (Yau et al.,
  1991)
• corn, soybean,
• sunflower oil linoleic acid (Scaife et al.,
  1990)
• linseed oil linolenic acid (Manilla, 1999)
• fish oil 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)

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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)

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• n-3 fatty acid enrichment foods
• No. 1. fish
• Other meats (pork, poultry)
• Egg
• Milk and milk products

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• 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 lt2.3 mmol/litre

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• Dietary fat affects blood lipids and blood
  clotting in the following ways
• 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 ?-6 series
• long-chain PUFA of the ?-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.