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General Information
• Definition
  – Substances found in living tissues which are
    generally insoluble in water and are...
General Information
• Use of fats and oils in body
  – Source of energy
     • For all cells except erythrocytes and cells...
General Information
 – Help provide food texture that increases
   palatability (i.e. improves mouthfeel)
 – Delays gastri...
General Information
• Metabolic energy from lipids
  – calorie = the quantity of heat required to raise
    the temperatur...
Kcals – Lauric Acid




CH3(CH2)10COOH +17O2   12CO2 + 12 H2O
Kcals – Lauric Acid
CH3(CH2)10COOH +17O2          12CO2 + 12 H2O
 Bond     Bond Energy   Number of bonds     Total Bond
  ...
Kcals – Lauric Acid
CH3(CH2)10COOH +17O2       12CO2 + 12 H2O
  Bond    Bond Energy   Number of
            (KJ/mol)     b...
Kcals – Lauric Acid
 CH3(CH2)10COOH +17O2            12CO2 + 12 H2O
    Bond     Bond Energy      Number of     Total Bond...
Kcals – Lauric Acid
6784 KJ/mol =   33.92 KJ/g
200.32 g/mol

33.92 KJ/g * 1 kcal    = 8.11kcal/g
             4.18 KJ
Nomenclature – fatty acids
• Nomenclature of fatty acids requires both a
  systematic approach and a knowledge of
  trivia...
Nomenclature – fatty acids
• Systematic
  – Names of fatty acids are derived from the
    appropriate parent hydrocarbon
 ...
Nomenclature – fatty acids
 – 2 main classes of fatty acids
    • Saturated: no double bonds
    • Unsaturated: double bon...
Nomenclature – fatty acids
• Trivial names
  – Names were selected prior to the identification of
    the fatty acid’s che...
Nomenclature – fatty acids
 – Examples:
   • Unsaturated
      –   C16:1: Palmitoleic
      –   C18:1: Oleic
      –   C18...
Nomenclature – fatty acids
• Location of the double bond (several ways to
  show this)
  – Delta notation (δ or Δ): termin...
Nomenclature – fatty acids
 – Omega notation (ω or η): terminal CH3 is #1
   • Example
      – Oleic acid: CH3(CH2)7CH=CH(...
Nomenclature – fatty acids
  • Most naturally occurring fatty acids have
    unconjugated double bonds
    – Double bonds ...
The Biochemical ω-system
• Animals cannot synthesize ω-3 or ω-6 fatty
  acids themselves
  – Animals lack the enzymes that...
Nomenclature – fatty acids
   • Using the omega notation can give necessary
     information in a brief way
      – Exampl...
Nomenclature – fatty acids
• What is the omega nomenclature of this
  fatty acid (please type into the chat
  space).
Nomenclature – fatty acids
• What is the delta nomenclature of this fatty
  acid (please type into the chat space).
  Incl...
Nomenclature – fatty acids
• What is the common (i.e. trivial) name of
  this fatty acid (please type into the chat
  spac...
Nomenclature – fatty acids
• Cis versus trans
   – Most unsaturated fatty acids in nature will exist in
     the cis confi...
EFA’s and deficiency
• Linoleic (18:2ω-6) deficiency
  – Clinical symptoms
     • Scaly skin, water loss through skin, ext...
Omega 3 fatty acids
  – 18:3ω-3 found in:
    •   Soybean oil (~7%)
    •   Canola oil (~10%)        VERY susceptible to
 ...
Omega 3 fatty acids
• Desaturated 20:5ω-3 (EPA) in marine oils
  – Studied Eskimos in Greenland: found a decrease
    in c...
Other fatty acids of interest
• Vaccenic acid
  – 18:1Δ-11trans (18:1ω-7trans); also 18:1Δ11
  – Trans fatty acids that oc...
Other fatty acids of interest
• Erucic acid
  – 22:1ω-9 rapeseed and mustard oils
  – Accumulates in heart tissue when fed...
Other fatty acids of interest
• Milk fat group
  – Fats derived from milk of domesticated land
    animals
     • Characte...
Other fatty acids of interest
• Lauric acid group
  – C12 is present
  – Coconut oil
• Vegetable butter group
  – Cocoa bu...
Other fatty acids of interest
• Linolenic acid group
  – Contains 18:3
  – Soybean oil ~8% 18:3
• Animal fat group
  – 30-...
Major Lipid Components –
Acylglycerols
• The majority of fatty acids are esterified to
  glycerol, making them acylglycero...
Major Lipid Components –
 Acylglycerols
 • Review of ester formation
      – Ester linkage forms between the carbon atom
 ...
Major Lipid Components –
Acylglycerols
   – Observe ester linkage
Glycerol                       Triacylglycerol = Triglyc...
General Lipid Categories
• Simple lipids (neutral lipids)
  – Esters of fatty acids and alcohols; lipids
    derived from ...
General Lipid Categories
• Compound (complex) lipids
  – Lipids containing other groups in addition to
    an alcohol-fatt...
General Lipid Categories
   • Example: cardiolipin (a phosphatidyl glycerol)
      – An important component of the inner m...
General Lipid Categories
        • Example: Phosphatidyl-
Choline (component of lecithin)    Ethanolamine (membrane lipid)...
General Lipid Categories
 – Sphingolipids
   • Associated with plant and animal membrane
     components
   • Play an impo...
General Lipid Categories
   • Examples
     – Sphingomyelin




     – Cerebrosides
General Lipid Categories
 – Sterols, other lipids and essential oils
    • All contain the cyclopentanoperhydrophenanthren...
General Lipid Categories
 – Sterols, other lipids and essential oils
    • Cholesterol: typical in animals
       – Plants...
General Lipid Categories
   • Phytosterols: plant sterols
      – Example: stigmasterol (in soybeans)
      – May reduce t...
General Lipid Categories
• Essential oils
  – Not “oils” in the real sense
     • Actually terpenes ((C5H8)n hydrocarbons)...
Natural fat and oil composition
• Fats of aquatic origin
  – Number of carbons usually exceeds 20
     • Mainly C14 – C24
...
Natural fat and oil composition
 – Other lipids present
   • Glycerol ethers
   • Waxes
      – Occur occasionally as an o...
Natural fat and oil composition
• Milk fats
  – Cow’s milk fat
     • High in C4 – C10 fatty acids: 20 – 30% on a molar
  ...
Natural fat and oil composition
• Vegetable fats (usually oils)
  – Present in all parts of plants but usually highest
   ...
Natural fat and oil composition
   • Example: Erucic acid (22:1Δ13) in rapeseed plant
      – No erucic acid in leaves
   ...
Natural fat and oil composition
   • Example: castor plant
      – Ricinoleic acid (12-OH 18:1)
      – Leaves: no ricinol...
Natural fat and oil composition
• Depot fats of land animals
  – Adipose tissue fat
     • Fats are laid down in adipose t...
Natural fat and oil composition
   • Characteristics
      –   Almost entirely C16 (32%) and C18 (62%) fatty acids
      –...
Natural fat and oil composition
• Summary
 – Animals do not generally produce linoleic and
   linolenic acids (EFA), thus ...
Lipid properties
Table 1. Physicochemical property comparison – Triolein oil vs. water

Property                          ...
Lipid properties
• Refractive index (RI)
  – Used to determine what the fatty acid
    composition might be
  – A ratio of...
Lipid properties
 – Extent of refraction depends on intermolecular
   attractions
   • Refraction
Lipid properties
     – Bending of light as it passes from one medium to another
     – The density of the medium impacts ...
Lipid properties
• Iodine value
  – The number of grams of iodine absorbed by 100
    grams of fat
  – Measure of the degr...
Lipid properties
 – The reaction results in addition to the double
   bond


     H H                   H H
              ...
Lipid properties
Calculation of Iodine Value – Oleic Acid
       CH3(CH2)7CH=CH(CH2)7COOH

1 mol of I2 adds across each do...
Calculation of Iodine Value: Oleic Acid (18:1Δ-9)
                 CH3(CH2)7CH=CH(CH2)7COOH

For each mol of lipid, 1 mol ...
Calculation of Iodine Value: Oleic Acid (18:1Δ-9)
                 CH3(CH2)7CH=CH(CH2)7COOH

For each mol of lipid, 1 mol ...
Calculation of Iodine Value: Oleic Acid (18:1Δ-9)
                 CH3(CH2)7CH=CH(CH2)7COOH

For each mol of lipid, 1 mol ...
Calculation of Iodine Value: Oleic Acid (18:1Δ-9)
                 CH3(CH2)7CH=CH(CH2)7COOH

For each mol of lipid, 1 mol ...
Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12)
          CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH
For each mol of lipi...
Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12)
          CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH
For each mol of lipi...
Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12)
          CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH
For each mol of lipi...
Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12)
          CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH
For each mol of lipi...
Lipid properties
• Saponification value
  – Number of mg of potassium hydroxide required
    to saponify with 1 gram of fa...
Lipid properties
 – If the triglyceride contains low molecular weight
   fatty acids, the number of molecules present in a...
Lipid properties
Table 1. Examples saponification and iodine numbers
Fat or oil        Saponification #    Iodine #
Beef t...
Modification of fats and oils
• Fats have the ability to enhance the
  palatability of foods
• Because of this there is a ...
Modification of fats and oils
      – Physical characteristics are influenced by:
           • Carbon chain length
       ...
Modification of fats and oils
• Modified in order to change the solid fat
  content (SFC) of lipids
  – The fraction or pe...
Modification of fats and oils
• Common processes for modifying lipids
  – Blending
  – Dietary interventions
  – Genetic m...
Modification of fats and oils
• Interesterification
  – Process used to improve the consistency of
    some natural fats t...
Modification of fats and oils
  – Process
    • Rearrangement of fatty acids so that they become
      distributed RANDOML...
Modification of fats and oils
    • Occurs within TAG’s or between TAG’s
    • Heat fat at high temperatures
    • Use a c...
Modification of fats and oils
Table 2. MP changes due to interesterification
Lipid                        MP (ºF) – Before...
Modification of fats and oils
• Hydrogenation
  – Very important to the oil industry
     • Need to modify natural liquid ...
Modification of fats and oils
 – Simple reaction
                                H H
 - C = C - + H2                -C-C-
...
Modification of fats and oils
 – Reasons for hydrogenation
   • Convert liquid fats into plastic fats (suitable for
     m...
Modification of fats and oils
 – General mechanism for hydrogenation
   • Requires a catalyst
      – Technically, it will...
Modification of fats and oils
                • Mechanism
                                               CH2-CH=CH-CH2-
  ...
Modification of fats and oils
 – Rate of reaction depends on:
   • Nature of substance being hydrogenated
      – The grea...
Modification of fats and oils
 – If unlimited H2 at catalyst surface:
    • Hydrogenation will be non-selective
       – S...
Modification of fats and oils
 – Partial hydrogenation (e.g. in soybean or
   vegetable oil)
   • In practice, partial hyd...
Modification of fats and oils
 – Testing partially hydrogenated oils
   • Samples are analyzed for
      –   Iodine value
...
Polling question - hydrogenation
Which fatty acid would hydrogenate faster:
 one with an IV of 103 or one with an IV
 of 8...
Deterioration reactions
• Autoxidation
  – General description
    • Atmospheric oxidation of fats and oils
  – General re...
Polling question - Autoxidation
Which of the following fatty acids is the most
  susceptible to autoxidation:

A.   Arachi...
Deterioration reactions
 – Mechanism of lipid oxidation
   • Free radical chain mechanism
   • Initiation
                ...
Deterioration reactions
   • Propagation
      – Alkyl radical (i.e. fatty acid free radical) combines with O2 to
        ...
Deterioration reactions
   • Termination
      – Reaction of 2 radicals, resulting in a non-propagating product


        ...
Deterioration reactions
 – Primary product = hydroperoxide (peroxide)
    • Measurement: peroxide value
      – Problem: h...
Deterioration reactions
 – Induction period (i.e. lag period)
    • No visible signs of oxidation occurring
       – Doesn...
Deterioration reactions
 – Antioxidants
   • Function to interrupt the free-radical mechanism
      – Extends the inductio...
Deterioration reactions
 – Initiation reaction
    • Subject of great interest
       – Common investigations: site of att...
Deterioration reactions
 – Oxidation of monoenoic acids
   • C8 and C11 are most likely sites for hydrogen removal
   • Th...
Deterioration reactions
                                 Oxidation of linoleic acid
                                      ...
Deterioration reactions
 – Aldehydes produced from various unsaturated fatty acids
    • Oleic acid
        Hydroperoxide ...
Deterioration reactions
   • Linoleic acid

      Hydroperoxide   Aldehyde formed
           C9         2, 4-decadienal
  ...
Deterioration reactions
   • Linolenic
     Hydroperoxide   Aldehyde formed
          C9         2, 4, 7-decatrienal
     ...
Deterioration reactions
 – Nutritional implications of autoxidation
    •   Loss of β-carotene (provitamin A)
    •   Loss...
Other deteriorative reactions
• Lipoxygenase reactions
  – Enzyme catalyzed lipid oxidation
  – Not the same mechanism as ...
Other deteriorative reactions
• Lipolysis
  – Hydrolysis reaction
     • Water is involved
     • Ester linkages can be br...
Other deteriorative reactions
• Lipolysis in heated fats – deep fat frying
  – Usually at temperatures > 180ºC
  – Results...
Other deteriorative reactions
 – Glycerol dehydration to acrolein (acrylaldehyde)
   • Moisture from food escapes and caus...
Other deteriorative reactions
• Thermal polymerization
  – When a fat/oil is heated to a high temperature
    (> 250ºC) in...
Other deteriorative reactions
 – Diels-Alder reaction
   • A conjugate addition reaction of a conjugated
     diene to an ...
Antioxidants
• General definition
  – Substances that slow or prevent oxidative
    reactions that would result in undesir...
Antioxidants
• Better definition
  – Compound which prevents rapid oxidation of
    food products by extending or prolongi...
Antioxidants
• Protection factor
  – Ratio:
             induction period protected
             induction period unprotec...
Antioxidants
• Mechanism of antioxidant action
  – Type I
    • Primary antioxidants
    • “Free radical chain stoppers”
 ...
Antioxidants
 – Type II
    • Inhibitors of free radical production in foods
    • Examples: EDTA, citric acid, phosphates...
Antioxidants
 – Type III
    • Elimination of environmental factors
    • Examples:
       – Lowering oxygen partial press...
Antioxidants
• Example mechanisms
  R· + AH     RH + A·

  RO· + AH     ROH + A·

  ROO· + AH       ROOH + A·

  R· + A·  ...
Antioxidants
• Competition between inhibitory reaction

  ROO· + AH        ROOH + A·

  and the chain propagating reaction...
Antioxidants
• Structures of synthetic antioxidants
                              OH




               OCH3          OCH3...
Antioxidants
  • Major antioxidants used in foods




2 and 3-tert-butyl-4-hydroxyanisole   butylated hydroxytoluene




 ...
Antioxidants
• Growing interest in natural antioxidants
  – Examples
     • Tocopherols
        – Principal antioxidant in...
Antioxidants
   • Ascorbic acid (i.e. vitamin C)
      – Works synergistically with vitamin E by regenerating it
Antioxidants
   • Chelating agents
      – Tie up metals
      – Examples:


      EDTA
                        Citric acid
Antioxidants
   • Plant extracts
      – Rosemary
         » Fresh
         » Not as effective as vitamin E, BHA, etc
    ...
Antioxidants
• Popular misconceptions of antioxidants
  – Improve flavor of poor quality fats and oils
  – Improve oil in ...
References
Gunstone F. 1999. Fatty Acid and Lipid Chemistry.
 Gaithersburg: Aspen Publishers, Inc.

McClements DJ and Deck...
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Lipid powerpoint Slide 1 Lipid powerpoint Slide 2 Lipid powerpoint Slide 3 Lipid powerpoint Slide 4 Lipid powerpoint Slide 5 Lipid powerpoint Slide 6 Lipid powerpoint Slide 7 Lipid powerpoint Slide 8 Lipid powerpoint Slide 9 Lipid powerpoint Slide 10 Lipid powerpoint Slide 11 Lipid powerpoint Slide 12 Lipid powerpoint Slide 13 Lipid powerpoint Slide 14 Lipid powerpoint Slide 15 Lipid powerpoint Slide 16 Lipid powerpoint Slide 17 Lipid powerpoint Slide 18 Lipid powerpoint Slide 19 Lipid powerpoint Slide 20 Lipid powerpoint Slide 21 Lipid powerpoint Slide 22 Lipid powerpoint Slide 23 Lipid powerpoint Slide 24 Lipid powerpoint Slide 25 Lipid powerpoint Slide 26 Lipid powerpoint Slide 27 Lipid powerpoint Slide 28 Lipid powerpoint Slide 29 Lipid powerpoint Slide 30 Lipid powerpoint Slide 31 Lipid powerpoint Slide 32 Lipid powerpoint Slide 33 Lipid powerpoint Slide 34 Lipid powerpoint Slide 35 Lipid powerpoint Slide 36 Lipid powerpoint Slide 37 Lipid powerpoint Slide 38 Lipid powerpoint Slide 39 Lipid powerpoint Slide 40 Lipid powerpoint Slide 41 Lipid powerpoint Slide 42 Lipid powerpoint Slide 43 Lipid powerpoint Slide 44 Lipid powerpoint Slide 45 Lipid powerpoint Slide 46 Lipid powerpoint Slide 47 Lipid powerpoint Slide 48 Lipid powerpoint Slide 49 Lipid powerpoint Slide 50 Lipid powerpoint Slide 51 Lipid powerpoint Slide 52 Lipid powerpoint Slide 53 Lipid powerpoint Slide 54 Lipid powerpoint Slide 55 Lipid powerpoint Slide 56 Lipid powerpoint Slide 57 Lipid powerpoint Slide 58 Lipid powerpoint Slide 59 Lipid powerpoint Slide 60 Lipid powerpoint Slide 61 Lipid powerpoint Slide 62 Lipid powerpoint Slide 63 Lipid powerpoint Slide 64 Lipid powerpoint Slide 65 Lipid powerpoint Slide 66 Lipid powerpoint Slide 67 Lipid powerpoint Slide 68 Lipid powerpoint Slide 69 Lipid powerpoint Slide 70 Lipid powerpoint Slide 71 Lipid powerpoint Slide 72 Lipid powerpoint Slide 73 Lipid powerpoint Slide 74 Lipid powerpoint Slide 75 Lipid powerpoint Slide 76 Lipid powerpoint Slide 77 Lipid powerpoint Slide 78 Lipid powerpoint Slide 79 Lipid powerpoint Slide 80 Lipid powerpoint Slide 81 Lipid powerpoint Slide 82 Lipid powerpoint Slide 83 Lipid powerpoint Slide 84 Lipid powerpoint Slide 85 Lipid powerpoint Slide 86 Lipid powerpoint Slide 87 Lipid powerpoint Slide 88 Lipid powerpoint Slide 89 Lipid powerpoint Slide 90 Lipid powerpoint Slide 91 Lipid powerpoint Slide 92 Lipid powerpoint Slide 93 Lipid powerpoint Slide 94 Lipid powerpoint Slide 95 Lipid powerpoint Slide 96 Lipid powerpoint Slide 97 Lipid powerpoint Slide 98 Lipid powerpoint Slide 99 Lipid powerpoint Slide 100 Lipid powerpoint Slide 101 Lipid powerpoint Slide 102 Lipid powerpoint Slide 103 Lipid powerpoint Slide 104 Lipid powerpoint Slide 105 Lipid powerpoint Slide 106 Lipid powerpoint Slide 107 Lipid powerpoint Slide 108 Lipid powerpoint Slide 109 Lipid powerpoint Slide 110 Lipid powerpoint Slide 111 Lipid powerpoint Slide 112 Lipid powerpoint Slide 113 Lipid powerpoint Slide 114 Lipid powerpoint Slide 115 Lipid powerpoint Slide 116 Lipid powerpoint Slide 117 Lipid powerpoint Slide 118 Lipid powerpoint Slide 119 Lipid powerpoint Slide 120 Lipid powerpoint Slide 121 Lipid powerpoint Slide 122 Lipid powerpoint Slide 123 Lipid powerpoint Slide 124 Lipid powerpoint Slide 125 Lipid powerpoint Slide 126
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Lipid powerpoint

  1. 1. General Information • Definition – Substances found in living tissues which are generally insoluble in water and are soluble in organic solvents (e.g. ether, chloroform, hexane) – Exceptions • Some lipids (such as short chain fatty acids - < 4 carbons long) are water soluble • Others are only soluble in a limited range of organic solvents
  2. 2. General Information • Use of fats and oils in body – Source of energy • For all cells except erythrocytes and cells of central nervous system (which use carbohydrates for the most part) – Carriers of fat-soluble vitamins (A, D, E, K) – Carrier of food flavors • Most dietary lipids are triglycerides which are relatively tasteless on their own
  3. 3. General Information – Help provide food texture that increases palatability (i.e. improves mouthfeel) – Delays gastric emptying (which contributes to satiety) – Adipose tissue insulates and cushions organs – Supplies essential fatty acids
  4. 4. General Information • Metabolic energy from lipids – calorie = the quantity of heat required to raise the temperature of 1.0 g of water by 1 degree Celsius (°C) – 1000 calories = 1 kilocalorie (abbreviated as kcal) = 1 Calorie (abbreviated as Cal) – In general, lipids are 9 kcal/g (or 9 C/g)
  5. 5. Kcals – Lauric Acid CH3(CH2)10COOH +17O2 12CO2 + 12 H2O
  6. 6. Kcals – Lauric Acid CH3(CH2)10COOH +17O2 12CO2 + 12 H2O Bond Bond Energy Number of bonds Total Bond (KJ/mol) Energy (KJ/mol) C-C 347 11 3817 C=O 799 1 799 C-O 351 1 351 O-H 460 1 460 C-H 414 23 9522 O=O 499 17 8483 23432
  7. 7. Kcals – Lauric Acid CH3(CH2)10COOH +17O2 12CO2 + 12 H2O Bond Bond Energy Number of (KJ/mol) bonds O-H 460 24 C=O 799 24
  8. 8. Kcals – Lauric Acid CH3(CH2)10COOH +17O2 12CO2 + 12 H2O Bond Bond Energy Number of Total Bond (KJ/mol) bonds Energy (KJ/mol) O-H 460 24 11040 C=O 799 24 19176 30216 30216 KJ/mol - 23432 KJ/mol = 6784 KJ/mol MWlauric acid: 200.32 g/mol
  9. 9. Kcals – Lauric Acid 6784 KJ/mol = 33.92 KJ/g 200.32 g/mol 33.92 KJ/g * 1 kcal = 8.11kcal/g 4.18 KJ
  10. 10. Nomenclature – fatty acids • Nomenclature of fatty acids requires both a systematic approach and a knowledge of trivial names
  11. 11. Nomenclature – fatty acids • Systematic – Names of fatty acids are derived from the appropriate parent hydrocarbon – Remove terminal “e” from parent and add suffix “oic” – Example • Hexane: CH3CH2CH2CH2CH2CH3 • Hexanoic acid: CH3(CH2)4COOH
  12. 12. Nomenclature – fatty acids – 2 main classes of fatty acids • Saturated: no double bonds • Unsaturated: double bonds present in carbon chain – If 1 double bond, the parent alkene becomes “enoic acid” • Example – 3-hexene: CH3CH2CH=CHCH2CH3 – 3-hexenoic acid: CH3CH2CH=CHCH2COOH – If 2 double bonds, use the suffix “dienoic” • Similarly for: – 3 double bonds, use “trienoic” – 4 double bonds, use “tetraenoic” – Etc.
  13. 13. Nomenclature – fatty acids • Trivial names – Names were selected prior to the identification of the fatty acid’s chemical structure – Name often identified the source of the fatty acid – Examples: • Saturated – C12: Lauric – C14: Myristic – C16: Palmitic – C18: Strearic – C20: Arachidic
  14. 14. Nomenclature – fatty acids – Examples: • Unsaturated – C16:1: Palmitoleic – C18:1: Oleic – C18:2: Linoleic – C18:3: Linolenic – C20:4: Arachidonic
  15. 15. Nomenclature – fatty acids • Location of the double bond (several ways to show this) – Delta notation (δ or Δ): terminal COOH is #1 • Example – Oleic acid: CH3(CH2)7CH=CH(CH2)7COOH » 9, 10-octadecenoic acid » Δ9-octadecenoic acid » 18:1Δ-9 – Linoleic acid: CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH » Δ9, 12-octadecadienoic acid » 18:2Δ-9,12
  16. 16. Nomenclature – fatty acids – Omega notation (ω or η): terminal CH3 is #1 • Example – Oleic acid: CH3(CH2)7CH=CH(CH2)7COOH » ω9-octadecenoic acid » 18:1ω-9 – Linoleic acid: CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH » ω6, 9-octadecadienoic acid » 18:2-ω6, 9
  17. 17. Nomenclature – fatty acids • Most naturally occurring fatty acids have unconjugated double bonds – Double bonds are separated by one or more single bonded C atoms – In most cases, double bonds are methylene interrupted Methylene group • CH2-CH=CH-CH2-CH=CH- • Conjugated double bonds – Double bonds adjacent to one another • CH2-CH=CH-CH=CH-
  18. 18. The Biochemical ω-system • Animals cannot synthesize ω-3 or ω-6 fatty acids themselves – Animals lack the enzymes that catalyze desaturation towards the methyl end • Enzymes in the body cannot function that close to the methyl end • Can elongate and desaturate towards carboxyl end – Plants and microorganisms can desaturate towards the methyl end Since animals cannot make 18:2ω-3 or 18:ω-6 , they are termed Essential Fatty Acids (EFA)
  19. 19. Nomenclature – fatty acids • Using the omega notation can give necessary information in a brief way – Example: What do we know from 18:2ω6? » 18 carbons » 2 double bonds » 1st double bond is 6 carbons down from the methyl end » Since we know that most double bonds are methylene interrupted, the 2nd double bond is 9 carbons down from the methyl end CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH
  20. 20. Nomenclature – fatty acids • What is the omega nomenclature of this fatty acid (please type into the chat space).
  21. 21. Nomenclature – fatty acids • What is the delta nomenclature of this fatty acid (please type into the chat space). Include all double bond locations.
  22. 22. Nomenclature – fatty acids • What is the common (i.e. trivial) name of this fatty acid (please type into the chat space).
  23. 23. Nomenclature – fatty acids • Cis versus trans – Most unsaturated fatty acids in nature will exist in the cis configuration • If the fatty acid is in the trans configuration, it will be stated – The two configurations will yield different properties at room temperature Oleic Acid: 18:1ω9 Elaidic Acid: 18:1ω9t Liquid at Troom Solid at Troom
  24. 24. EFA’s and deficiency • Linoleic (18:2ω-6) deficiency – Clinical symptoms • Scaly skin, water loss through skin, extreme thirst, poor wound healing, failure to gain weight, impaired reproduction, death • Linolenic (18:3ω-3) deficiency – Noticed symptoms • Blurred vision, neurological symptoms, tingling extremities – Linolenic is critical to prostaglandin formation
  25. 25. Omega 3 fatty acids – 18:3ω-3 found in: • Soybean oil (~7%) • Canola oil (~10%) VERY susceptible to oxidative rancidity = • Linseed oil (~50-60%) degradation • Green leafy vegetables • Desaturated 20:5ω-3 (EPA) in marine oils – Studied Eskimos in Greenland: found a decrease in coronary heart disease compared to populations consuming less marine foods
  26. 26. Omega 3 fatty acids • Desaturated 20:5ω-3 (EPA) in marine oils – Studied Eskimos in Greenland: found a decrease in coronary heart disease compared to populations consuming less marine foods
  27. 27. Other fatty acids of interest • Vaccenic acid – 18:1Δ-11trans (18:1ω-7trans); also 18:1Δ11 – Trans fatty acids that occur in milk and butterfat due to biohydrogenation in rumen • Ricinoleic acid – 12-OH octadeca cis-9-enoic acid – Oleic acid with an OH group on carbon 12 from COOH end – Castor oil • Laxative
  28. 28. Other fatty acids of interest • Erucic acid – 22:1ω-9 rapeseed and mustard oils – Accumulates in heart tissue when fed to rats – Genetic variant is canola oil, or low erucic acid rapeseed (LEAR) • Branched chain – Iso: mainly even C’s – Anteiso: mainly odd C’s – Occur in waxes like wool wax
  29. 29. Other fatty acids of interest • Milk fat group – Fats derived from milk of domesticated land animals • Characteristic shorter chain fatty acids (C4 – C12) in milk fat – Influences milk flavor and how milk is processed into dairy products • C4: butyric acid – A fatty acid that is liquid at Troom although saturated – Normally masked in foods – If broken down via lipolysis, it will be very pungent » Occurs due to extreme heat or agitation
  30. 30. Other fatty acids of interest • Lauric acid group – C12 is present – Coconut oil • Vegetable butter group – Cocoa butter • Oleic-linoleic acid group – MAJOR GROUP – Vegetable oils – Saturated acids >20%
  31. 31. Other fatty acids of interest • Linolenic acid group – Contains 18:3 – Soybean oil ~8% 18:3 • Animal fat group – 30-40% saturated – ~60% unsaturated – Lard, tallow • Marine fat group – Highly unsaturated
  32. 32. Major Lipid Components – Acylglycerols • The majority of fatty acids are esterified to glycerol, making them acylglycerols • Triacylglycerols are the most common in foods – Mono- and diacylglycerols do exist as food additives
  33. 33. Major Lipid Components – Acylglycerols • Review of ester formation – Ester linkage forms between the carbon atom of carboxylic acid on the fatty acid chain and the oxygen atom of the alcohol on the glycerol backbone O O R-C-OH + R’OH R-C-OR’ + H2O O R : Fatty acid chain C-OH : Carboxylic acid OH : Alcohol
  34. 34. Major Lipid Components – Acylglycerols – Observe ester linkage Glycerol Triacylglycerol = Triglyceride H H O H-C-OH H-C-O-C-R1 H-C-OH + 3 fatty acids O + 3 H2O H-C-OH H-C-O-C-R2 O H H-C-O-C-R3 1 mol of water is given off for every mol of “R” H participating in the reaction
  35. 35. General Lipid Categories • Simple lipids (neutral lipids) – Esters of fatty acids and alcohols; lipids derived from these by alkaline and acid hydrolysis (derived lipids) – Includes fatty acids, glycerides, fatty alcohols – Examples • Triacylglycerols (i.e. triglycerides) – Esters of fatty acids and glycerol • Waxes – Esters of fatty acids with alcohols other than glycerol – Normally: long chain alcohols (e.g. C24) – Water insoluble
  36. 36. General Lipid Categories • Compound (complex) lipids – Lipids containing other groups in addition to an alcohol-fatty acid ester linkage – Phospholipids • Phosphoglycerides or glycerophospholipids • Glycerol + fatty acids + phosphate + another group • Example: phosphatidic acid (major component of cell membranes)
  37. 37. General Lipid Categories • Example: cardiolipin (a phosphatidyl glycerol) – An important component of the inner mitochondrial membrane – Important to the electron transport chain that produces ATP
  38. 38. General Lipid Categories • Example: Phosphatidyl- Choline (component of lecithin) Ethanolamine (membrane lipid) Serine (for NS cell functioning) Inositol (substrate for cell signaling enzymes)
  39. 39. General Lipid Categories – Sphingolipids • Associated with plant and animal membrane components • Play an important role in both signal transmission and cell recognition • Sphingosine + derived lipids + water soluble products – No glycerol backbone
  40. 40. General Lipid Categories • Examples – Sphingomyelin – Cerebrosides
  41. 41. General Lipid Categories – Sterols, other lipids and essential oils • All contain the cyclopentanoperhydrophenanthrene ring system http://journals.iucr.org/a/issues/2006/02/00/xo5005/xo5005fig1.html
  42. 42. General Lipid Categories – Sterols, other lipids and essential oils • Cholesterol: typical in animals – Plants do have detectable levels, but VERY low – Has the ability to undergo oxidation, leading to heart disease and cancer » Low density lipoprotein oxidation can lead to plaque
  43. 43. General Lipid Categories • Phytosterols: plant sterols – Example: stigmasterol (in soybeans) – May reduce the risk of CHD by lowering blood cholesterol levels
  44. 44. General Lipid Categories • Essential oils – Not “oils” in the real sense • Actually terpenes ((C5H8)n hydrocarbons) – Often mixed with other lipids in waxy coats or located in special oil sacs in the skin of citrus fruits – Important to citrus-based flavor development
  45. 45. Natural fat and oil composition • Fats of aquatic origin – Number of carbons usually exceeds 20 • Mainly C14 – C24 – Major saturated acid is palmitic (16:0): 15-20% by wt. – Monoenoic acids are 16:1, 18:1, and 20:1 • Usually with double bond position at 9, but some have double bond at carbon 1 – Many C16, C18, C20, and C22 polyenoic acids • ω3 family: 18:3, 18:4, 20:4, 20:5, 22:5, and 22:6
  46. 46. Natural fat and oil composition – Other lipids present • Glycerol ethers • Waxes – Occur occasionally as an oil of the sperm whale – Ester of long chain alcohol and a fatty acid
  47. 47. Natural fat and oil composition • Milk fats – Cow’s milk fat • High in C4 – C10 fatty acids: 20 – 30% on a molar basis – Human milk fat • Much lower in C4 – C10, but higher in C12 – C14
  48. 48. Natural fat and oil composition • Vegetable fats (usually oils) – Present in all parts of plants but usually highest in fleshy part of fruit or in seeds (seed oils) – Oils and fats from different parts of plant differ in composition
  49. 49. Natural fat and oil composition • Example: Erucic acid (22:1Δ13) in rapeseed plant – No erucic acid in leaves – In rapeseed oil, there’s approximately 40 – 50% erucic acid – Problem » Erucic acid accumulates in heart muscle, not in adipose tissue, upon feeding » Heart lacks enzyme for oxidizing erucic acid » Could be a problem if an excess of one fatty acid accumulates in heart muscle membranes » The problem was avoided with the development of low erucic acid rapeseed oil (LEAR)
  50. 50. Natural fat and oil composition • Example: castor plant – Ricinoleic acid (12-OH 18:1) – Leaves: no ricinoleic acid – Castor oil: ~90 ricnioleic acid
  51. 51. Natural fat and oil composition • Depot fats of land animals – Adipose tissue fat • Fats are laid down in adipose tissue as triglycerides • Two sources of fatty acids – Endogenous supply from CHO and protein synthesis – Dietary fat (this may be modified by the animal) • Easy to distinguish from fish oils as they are solid or semi-solid at Troom
  52. 52. Natural fat and oil composition • Characteristics – Almost entirely C16 (32%) and C18 (62%) fatty acids – C16 is almost all 16:0 – C18 is almost all 18:1 – Stearic-rich (18:0) fats come from ruminants such as sheep, cattle, and deer » Hydrogenation of fatty acids by rumen bacteria » Also due to hydrogenation in rumen, small amounts of trans fatty acids » The fatty acid composition of adipose tissue can be changed drastically by changing animal’s diet – pig feed high in 18:2 (corn) can result in “soft-pork” problem (i.e. soft adipose tissue = runny fat)
  53. 53. Natural fat and oil composition • Summary – Animals do not generally produce linoleic and linolenic acids (EFA), thus they must acquire it from their diet – Plants produce linoleic and linolenic, but carry out less conversion to the longer, more unsaturated fatty acids – Microorganisms are versatile • They can produce all kinds of fatty acids including branched chain, hydroxyl, keto, and cyclic fatty acids
  54. 54. Lipid properties Table 1. Physicochemical property comparison – Triolein oil vs. water Property Oil Water Molecular weight 885 18 Melting point (ºC) 5 0 Density (kg/m3) 910 998 Viscosity (mPa*s) ~50 1.002 Specific heat (J/kg*K) 1980 4182 Refractive index 1.46 1.33
  55. 55. Lipid properties • Refractive index (RI) – Used to determine what the fatty acid composition might be – A ratio of the velocity of light in air to the velocity of light in the substance – A function of the temperature and wavelength of light employed
  56. 56. Lipid properties – Extent of refraction depends on intermolecular attractions • Refraction
  57. 57. Lipid properties – Bending of light as it passes from one medium to another – The density of the medium impacts the speed of light through the medium » This causes the light to bend at different angles – Extent of refraction is also impacted by intermolecular attractions – RI increases with increasing chain length and with increasing unsaturation (i.e. number of double bonds) – Use in industry » As a control procedure during hydrogenation (a change in RI results when the number of double bonds changes)
  58. 58. Lipid properties • Iodine value – The number of grams of iodine absorbed by 100 grams of fat – Measure of the degree of UNsaturation – Halogens (e.g. Cl, Br, I) react with double bonds in fatty acids under mild conditions
  59. 59. Lipid properties – The reaction results in addition to the double bond H H H H I2 -C=C- -C - C- I I
  60. 60. Lipid properties Calculation of Iodine Value – Oleic Acid CH3(CH2)7CH=CH(CH2)7COOH 1 mol of I2 adds across each double bond – therefore, in the case of oleic acid, 1 mol of I2 will add across the 1 double bond in oleic acid
  61. 61. Calculation of Iodine Value: Oleic Acid (18:1Δ-9) CH3(CH2)7CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of oleic acid, with one double bond, 1 mol of I2 will add to 1 mol of oleic acid. Since we know the molecular weights of both oleic acid (282g/mol) and I2 (254g/mol) we can establish a mass ratio on a per mol basis that we can use to calculate how many grams of I2 will add across 100g of oleic acid. In other words, if 1 mol of I2 adds to 1 mol of oleic acid, then 254g of I2 add to 282 g of oleic acid. Thus, we can determine how many grams of I2 add to 100g of oleic using the following ratio:
  62. 62. Calculation of Iodine Value: Oleic Acid (18:1Δ-9) CH3(CH2)7CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of oleic acid, with one double bond, 1 mol of I2 will add to 1 mol of oleic acid. Since we know the molecular weights of both oleic acid (282g/mol) and I2 (254g/mol) we can establish a mass ratio on a per mol basis that we can use to calculate how many grams of I2 will add across 100g of oleic acid. In other words, if 1 mol of I2 adds to 1 mol of oleic acid, then 254g of I2 add to 282 g of oleic acid. Thus, we can determine how many grams of I2 add to 100g of oleic using the following ratio: 254gI2 XgI2 = 282gOleic Acid 100gOleic Acid
  63. 63. Calculation of Iodine Value: Oleic Acid (18:1Δ-9) CH3(CH2)7CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of oleic acid, with one double bond, 1 mol of I2 will add to 1 mol of oleic acid. Since we know the molecular weights of both oleic acid (282g/mol) and I2 (254g/mol) we can establish a mass ratio on a per mol basis that we can use to calculate how many grams of I2 will add across 100g of oleic acid. In other words, if 1 mol of I2 adds to 1 mol of oleic acid, then 254g of I2 add to 282 g of oleic acid. Thus, we can determine how many grams of I2 add to 100g of oleic using the following ratio: 254gI2 XgI2 = 282gOleic Acid 100gOleic Acid (254gI2)(100gOleic Acid) = (XgI2)(282gOleic Acid) X = 90gI2
  64. 64. Calculation of Iodine Value: Oleic Acid (18:1Δ-9) CH3(CH2)7CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of oleic acid, with one double bond, 1 mol of I2 will add to 1 mol of oleic acid. Since we know the molecular weights of both oleic acid (282g/mol) and I2 (254g/mol) we can establish a mass ratio on a per mol basis that we can use to calculate how many grams of I2 will add across 100g of oleic acid. In other words, if 1 mol of I2 adds to 1 mol of oleic acid, then 254g of I2 add to 282 g of oleic acid. Thus, we can determine how many grams of I2 add to 100g of oleic using the following ratio: 254gI2 XgI2 = 282gOleic Acid 100gOleic Acid (254gI2)(100gOleic Acid) = (XgI2)(282gOleic Acid) X = 90gI2 meaning that 90g of I2 will add to 100g of oleic acid
  65. 65. Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12) CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of linoleic acid, with two double bonds, 2 moles of I2 will add to 1 mol of linoleic acid. The MW of linoleic acid is 280g/mol and the MW of I2 is 254g/mol. We can establish the mass ratio to calculate how many grams of I2 will add across 100g of linoleic acid. Remember that 2 moles of I2 add to 1 mol of linoleic acid, so (254g/mol * 2 moles) of I2 add to (282 g/mol * 1 mol) of linoleic acid.
  66. 66. Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12) CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of linoleic acid, with two double bonds, 2 moles of I2 will add to 1 mol of linoleic acid. The MW of linoleic acid is 280g/mol and the MW of I2 is 254g/mol. We can establish the mass ratio to calculate how many grams of I2 will add across 100g of linoleic acid. Remember that 2 moles of I2 add to 1 mol of linoleic acid, so (254g/mol * 2 moles) of I2 add to (282 g/mol * 1 mol) of linoleic acid. 508gI2 XgI2 = 280gLinoleic Acid 100gLinoleic Acid
  67. 67. Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12) CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of linoleic acid, with two double bonds, 2 moles of I2 will add to 1 mol of linoleic acid. The MW of linoleic acid is 280g/mol and the MW of I2 is 254g/mol. We can establish the mass ratio to calculate how many grams of I2 will add across 100g of linoleic acid. Remember that 2 moles of I2 add to 1 mol of linoleic acid, so (254g/mol * 2 moles) of I2 add to (282 g/mol * 1 mol) of linoleic acid. 508gI2 XgI2 = 280gLinoleic Acid 100gLinoleic Acid (508gI2)(100gOleic Acid) = (XgI2)(280gOleic Acid) X = 181gI2
  68. 68. Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12) CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of linoleic acid, with two double bonds, 2 moles of I2 will add to 1 mol of linoleic acid. The MW of linoleic acid is 280g/mol and the MW of I2 is 254g/mol. We can establish the mass ratio to calculate how many grams of I2 will add across 100g of linoleic acid. Remember that 2 moles of I2 add to 1 mol of linoleic acid, so (254g/mol * 2 moles) of I2 add to (282 g/mol * 1 mol) of linoleic acid. 508gI2 XgI2 = 280gLinoleic Acid 100gLinoleic Acid (508gI2)(100gOleic Acid) = (XgI2)(280gOleic Acid) X = 181gI2 meaning that 181g of I2 will add to 100g of linoleic acid
  69. 69. Lipid properties • Saponification value – Number of mg of potassium hydroxide required to saponify with 1 gram of fat or oil – 3 moles of KOH react with on mol of triacylglycerol
  70. 70. Lipid properties – If the triglyceride contains low molecular weight fatty acids, the number of molecules present in a 1 gram sample of the fat will be greater than if the fatty acids have long carbon chains and high molecular weights • The fat with the lower molecular weight fatty acids will consequently have a higher saponification value • Butter, for example, with a high percentage of butyric acid, has a high saponification value
  71. 71. Lipid properties Table 1. Examples saponification and iodine numbers Fat or oil Saponification # Iodine # Beef tallow 194 – 200 34 – 43 Cocoa butter 192 – 198 32 – 42 Coconut oil 245 – 262 6 – 10 Cottonseed oil 192 – 196 103 – 112 Lard 193 – 200 50 – 80 Milk fat 210 – 233 26 – 35 Peanut oil 186 – 194 89 – 98
  72. 72. Modification of fats and oils • Fats have the ability to enhance the palatability of foods • Because of this there is a great emphasis on the crystallization and melting behavior of fats • Unique fatty acid distribution of some natural fats makes them undesirable for certain applications
  73. 73. Modification of fats and oils – Physical characteristics are influenced by: • Carbon chain length – Increased chain length = increased melting point • Degree of unsaturation – The more unsaturated a fatty acid is, the more liquid it will be at Troom • Distribution of fatty acids on glycerol monoglyceride diglyceride triglyceride
  74. 74. Modification of fats and oils • Modified in order to change the solid fat content (SFC) of lipids – The fraction or percentage of a lipid that is solid at a given temperature – Enables less expensive lipids to be used – Can reduce unsaturation, reducing susceptibility to oxidation – Can also increase unsaturation, potentially increasing nutritional quality
  75. 75. Modification of fats and oils • Common processes for modifying lipids – Blending – Dietary interventions – Genetic manipulation – Fractionation – Interesterification – Hydrogenation
  76. 76. Modification of fats and oils • Interesterification – Process used to improve the consistency of some natural fats to enhance their usefulness – Alteration of the original fatty acid distribution on the glycerol backbone • Affects melting and crystallization properties • Rearrangement at random
  77. 77. Modification of fats and oils – Process • Rearrangement of fatty acids so that they become distributed RANDOMLY among the TAG molecules • Mixing of 2 esters resulting in the exchange of “R” groups O O R1C – O – CH3 + R2C – O – C2H5 O O R1C – O – C2H5 + R2C – O – CH3
  78. 78. Modification of fats and oils • Occurs within TAG’s or between TAG’s • Heat fat at high temperatures • Use a catalyst to speed up the reaction – Most popular: NaOCH3 (sodium methoxide) – Alteration of physical properties of fats and oils • Example: cocoa butter (mp 28 – 30ºC) – Cocoa butter has a characteristic fatty acid composition and distribution » “Melts in your mouth, not in your hands” – Once cocoa butter undergoes radomization by interesterification, it no longer melts at the same temperature
  79. 79. Modification of fats and oils Table 2. MP changes due to interesterification Lipid MP (ºF) – Before MP (ºF) – After Soybean oil 19.4 41.9 Cottonseed oil 50.9 93.2 Coconut oil 78.8 82.8 Palm oil 103.7 116.6 Lard 109.5 109.5 Tallow 115.2 112.3 40% hydrog. cottonseed oil 136.0 106.0 23% hydrog. palm oil 122.3 104.5
  80. 80. Modification of fats and oils • Hydrogenation – Very important to the oil industry • Need to modify natural liquid oils to make fats with a wide range of properties – Soft and greasy to hard and brittle • Usually only partial hydrogenation occurs
  81. 81. Modification of fats and oils – Simple reaction H H - C = C - + H2 -C-C- H H H H • Addition of H2 across double bonds makes compounds saturated • Alters: – Molecular configuration – Number, geometry and location of double bonds Most importantly, it can result in the formation of trans fatty acids!!!
  82. 82. Modification of fats and oils – Reasons for hydrogenation • Convert liquid fats into plastic fats (suitable for manufacture of shortenings and margarine) • Improve resistance of fats and oils to deterioration through oxidation or flavor reversion • Convert soft fats into firmer fats • Improve color
  83. 83. Modification of fats and oils – General mechanism for hydrogenation • Requires a catalyst – Technically, it will happen naturally, however, the reaction will take place VERY slowly – Usually nickel – Heterogeneous » In other words, the catalyst is in a different chemical state (typically solid when hydrogenating a liquid oil)
  84. 84. Modification of fats and oils • Mechanism CH2-CH=CH-CH2- Absorption of fatty acid onto catalyst Ni Ni CH2-CH-CH-CH2- Double bond is broken and 2C-Ni bonds form Reaction with absorbed H goes to partially hydrogenated states Ni Ni CH2-CH2-CH-CH2- + CH2-CH-CH2 -CH2- These may then go either of two ways H desorption from catalyst Loses H from a C atom adjacent to a C-Ni bond CH2-CH2-CH=CH- Double bond will CH2-CH2-CH2-CH2- be cis or trans Fully hydrogenated CH=CH-CH2-CH2- These fatty acids can go back into CH2-CH=CH-CH2- the cycle
  85. 85. Modification of fats and oils – Rate of reaction depends on: • Nature of substance being hydrogenated – The greater the number of double bonds, the faster the reaction • Nature and concentration of the catalyst • Concentration of H2 • Temperature, pressure and degree of agitation – Increasing the temperature, pressure of H2 and degree of agitation will all speed up the reaction
  86. 86. Modification of fats and oils – If unlimited H2 at catalyst surface: • Hydrogenation will be non-selective – Selectivity: the tendency for more unsaturated fatty acids to be reduced before those fatty acids that are more saturated » Example: 18:3 are hydrogenated before 18:2 which are hydrogenated before 18:1 • Any factor influencing the amount of H2 at the catalyst surface will influence the rate and selectivity • Control of selectivity – Increase selectivity by reducing H2 at the catalyst surface » Increase T, decrease P, increase amount of catalyst
  87. 87. Modification of fats and oils – Partial hydrogenation (e.g. in soybean or vegetable oil) • In practice, partial hydrogenation is carried out in vessels known as “converters” • Closed, pressurized vessels with a capacity of ~60,000 pounds • Agitation, heating, cooling and H2 inlet/vent systems • Temperature ~ 175ºC • Typical catalyst is Ni (0.01 – 0.02% of oil) • H2 at 5 – 50 psi • After partial hydrogenation, the oil is cooled, drained and the catalyst is removed by filtration
  88. 88. Modification of fats and oils – Testing partially hydrogenated oils • Samples are analyzed for – Iodine value – Refractive index (AOCS method) – Melting point – Infrared spectroscopy (IR)
  89. 89. Polling question - hydrogenation Which fatty acid would hydrogenate faster: one with an IV of 103 or one with an IV of 80?
  90. 90. Deterioration reactions • Autoxidation – General description • Atmospheric oxidation of fats and oils – General reaction characteristics • Autocatalytic • Has an induction point • Accelerated by metals, light, and temperature • Surface dependent • Unsaturation dependent • Produces a variety of oxidation products
  91. 91. Polling question - Autoxidation Which of the following fatty acids is the most susceptible to autoxidation: A. Arachidic B. Arachidonic C. Palmitoleic D. Myristic
  92. 92. Deterioration reactions – Mechanism of lipid oxidation • Free radical chain mechanism • Initiation Alkyl radical RH R· + H· – Removal of a H atom from a C adjacent to a double bond – H atom is usually from the methylene group – Example: R-CH=CH-CH2-R’ R-CH=CH-C·H-R’ Methylene group
  93. 93. Deterioration reactions • Propagation – Alkyl radical (i.e. fatty acid free radical) combines with O2 to first form peroxy radical R· + O2 ROO· Peroxy radical: initial product during propagation – Peroxy radical then combines with fatty acid to form hydroperoxide and another alkyl radical ROO· + RH ROOH + R· Hydroperoxide
  94. 94. Deterioration reactions • Termination – Reaction of 2 radicals, resulting in a non-propagating product R· + R· RR ROO· + ROO· ROOR + O2 RO· + R· ROR ROO· + R· ROOR 2RO· + 2ROO· 2ROOR + O2
  95. 95. Deterioration reactions – Primary product = hydroperoxide (peroxide) • Measurement: peroxide value – Problem: hydroperoxide decomposition » Example: break down product = hexanal Concentration Hexanal Time » When measuring PV, the value rapidly increases after lag period, but then decreases as hydoperoxide decomposes
  96. 96. Deterioration reactions – Induction period (i.e. lag period) • No visible signs of oxidation occurring – Doesn’t mean that oxidation isn’t occurring, though • During the initiation phase – Symbolizes reactants coming together
  97. 97. Deterioration reactions – Antioxidants • Function to interrupt the free-radical mechanism – Extends the induction period – Delays the onset of oxidative rancidity • Limit on the amount of an antioxidant that can be used – 0.02% of the weight of the fat • Must be added at the beginning of a process to be most effective
  98. 98. Deterioration reactions – Initiation reaction • Subject of great interest – Common investigations: site of attack, energy requirements • H atom adjacent to double bond is most susceptible – Easy to remove because of neighboring double bond • Unsure where 1st radical comes from in foods – Perhaps singlet oxygen – Trace metals may initiate the reaction (e.g. Cu, Fe)
  99. 99. Deterioration reactions – Oxidation of monoenoic acids • C8 and C11 are most likely sites for hydrogen removal • They then react with O2 and attack another RH resulting in hydroperoxide formation • Hydroperoxide decomposes to aldehydes, alcohols and ketones • 4 free radicals/4 hydroperoxides – Decompose » Aldehyde production common » Trace metals, temperature and light accelerate hydroperoxide decomposition
  100. 100. Deterioration reactions Oxidation of linoleic acid 9 10 11 12 13 -CH=CH-CH2-CH=CH- Loss of proton 9 10 11 12 13 -CH=CH-CH-CH=CH- Double bond shift for isomerization 9 10 11 12 13 9 10 11 12 13 -CH-CH=CH-CH=CH- -CH=CH-CH=CH-CH- O2, RH O2, RH 9 10 11 12 13 9 10 11 12 13 -CH-CH=CH-CH=CH- -CH=CH-CH=CH-CH- Decomposition of OOH Decomposition of hydroperoxide OOH O hydroperoxide O 10 11 12 13 13 14 15 16 17 18 9 C-CH=CH-CH=CH-(CH2)4-CH3 C-CH2-CH2-CH2-CH2-CH3 H 2, 4-decadienal H Hexanal
  101. 101. Deterioration reactions – Aldehydes produced from various unsaturated fatty acids • Oleic acid Hydroperoxide Aldehyde formed C8 2-undecenal C9 2-decenal C10 n-nonanol C11 n-octanol
  102. 102. Deterioration reactions • Linoleic acid Hydroperoxide Aldehyde formed C9 2, 4-decadienal C11 2-octenal C13 n-hexanal
  103. 103. Deterioration reactions • Linolenic Hydroperoxide Aldehyde formed C9 2, 4, 7-decatrienal C11 2, 5-octadienal C12 2, 4-heptadienal C13 3-hexenal C14 2-pentenal C16 propanol
  104. 104. Deterioration reactions – Nutritional implications of autoxidation • Loss of β-carotene (provitamin A) • Loss of fat-soluble vitamins (A, D, E, K) • Loss of essential fatty acids • Possible build up of polymeric material • Loss of protein quality – Free radicals will react with protein – Carbonyl-amine reactions (i.e. Maillard browning reaction) – Other implications • Loss of color and flavor = shelf life limitations • Warmed over flavors in refrigerated foods
  105. 105. Other deteriorative reactions • Lipoxygenase reactions – Enzyme catalyzed lipid oxidation – Not the same mechanism as autoxidation – Common reaction in soybeans
  106. 106. Other deteriorative reactions • Lipolysis – Hydrolysis reaction • Water is involved • Ester linkages can be broken by re-addition of water produced when ester linkage is created – Can occur due to enzymes, thermal stresses (e.g. heat, moisture) – Known as: • Lipolysis, lipolytic rancidity, hydrolysis, hydrolytic rancidity DO NOT CONFUSE WITH OXIDATIVE RANCIDITY!!!
  107. 107. Other deteriorative reactions • Lipolysis in heated fats – deep fat frying – Usually at temperatures > 180ºC – Results when oil is reused – Moisture from food can cause hydrolysis (i.e. lipolysis) – Causes color changes (i.e. darkening) , an increase in viscosity, a decrease in smoke point, and potentially toxic products
  108. 108. Other deteriorative reactions – Glycerol dehydration to acrolein (acrylaldehyde) • Moisture from food escapes and causes oil to hydrolyze into glycerol and free fatty acid(s) Glycerol Acrolein H H O H-C-OH C -H2O H-C-OH C-H Heat H-C-OH C-H H H • Responsible for puffs of smoke – Very pungent – choking irritating odor • Results in smoke point depression
  109. 109. Other deteriorative reactions • Thermal polymerization – When a fat/oil is heated to a high temperature (> 250ºC) in the absence of oxygen – Also occurs during deep fat frying
  110. 110. Other deteriorative reactions – Diels-Alder reaction • A conjugate addition reaction of a conjugated diene to an alkene (the dienophile) to produce a cyclohexene + Conjugated Dienophile Cyclic diene adduct http://www.chem.ucalgary.ca/courses/351/Carey/Ch10/ch10-5.html 1, 3-butadiene Acrolein 1, 2, 3, 6 –tetrahydro benzaldehyde CH2 H O •Can cause HC C CHO color and + viscosity C-H changes HC •Also, can be CH2 C-H carcinogenic H
  111. 111. Antioxidants • General definition – Substances that slow or prevent oxidative reactions that would result in undesirable changes • Examples: the development of off-flavors, discoloration, and loss of nutritive value – Antioxidants – Synergists – Oxygen displacers (e.g. inert gases) – Protective coatings
  112. 112. Antioxidants • Better definition – Compound which prevents rapid oxidation of food products by extending or prolonging the induction period
  113. 113. Antioxidants • Protection factor – Ratio: induction period protected induction period unprotected
  114. 114. Antioxidants • Mechanism of antioxidant action – Type I • Primary antioxidants • “Free radical chain stoppers” – Interacts with free radicals produced during the initiation phase (e.g. R· or ROO·) • Normally phenolic (e.g. BHA, BHT) OH H atom interacts with R· or ROO· to form RH or ROOH
  115. 115. Antioxidants – Type II • Inhibitors of free radical production in foods • Examples: EDTA, citric acid, phosphates, and phosphoric acid – Tie up metal catalysts
  116. 116. Antioxidants – Type III • Elimination of environmental factors • Examples: – Lowering oxygen partial pressure in a package » Vacuum, inert gas, airtight containers – Lowering temperatures » -12 to 20ºC – Exclusion of light – Prevention of contamination by catalytic, prooxidative metals
  117. 117. Antioxidants • Example mechanisms R· + AH RH + A· RO· + AH ROH + A· ROO· + AH ROOH + A· R· + A· RA RO· + A· ROA
  118. 118. Antioxidants • Competition between inhibitory reaction ROO· + AH ROOH + A· and the chain propagating reaction ROO· + RH ROOH + R·
  119. 119. Antioxidants • Structures of synthetic antioxidants OH OCH3 OCH3 anisole hydroxyanisole OH CH3 CH3 toluene hydroxytoluene
  120. 120. Antioxidants • Major antioxidants used in foods 2 and 3-tert-butyl-4-hydroxyanisole butylated hydroxytoluene propyl gallate
  121. 121. Antioxidants • Growing interest in natural antioxidants – Examples • Tocopherols – Principal antioxidant in vegetable oils » Most widely distributed antioxidants in nature – Example: vitamin E
  122. 122. Antioxidants • Ascorbic acid (i.e. vitamin C) – Works synergistically with vitamin E by regenerating it
  123. 123. Antioxidants • Chelating agents – Tie up metals – Examples: EDTA Citric acid
  124. 124. Antioxidants • Plant extracts – Rosemary » Fresh » Not as effective as vitamin E, BHA, etc – Soybean – Honey
  125. 125. Antioxidants • Popular misconceptions of antioxidants – Improve flavor of poor quality fats and oils – Improve oil in which oxidative ancidity has developed – Prevent microbial decay – Prevent hydrolytic rancidity
  126. 126. References Gunstone F. 1999. Fatty Acid and Lipid Chemistry. Gaithersburg: Aspen Publishers, Inc. McClements DJ and Decker EA. 2007. Lipids. In: Fennema's Food Chemistry (4th Edition). Damodaran S, Parkin KL, Fennema OR eds. Boca Raton: CRC Press. P 155-212. Nawar WW. 1996. Lipids. In: Food Chemistry (3rd edition) Fennema OR, editor. New York: Marcel Dekker, Inc. p 225-320.
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