Module 4. Lipids

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Module 4. Lipids

• Food Chemistry 2
• ND Food Technology

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Table of Contents

• Introduction
• Classification
• Fatty acids
• Gliserides
• Phospholipids
• Unsaponifiables
• Emulsions emulsifiers
• Physical properties of oils fats
• Cocoa butter confectionary fats
• Heated fats - frying

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1. Introduction

• Difficult to give definitions too many
  different types usually water-insoluble organic
  compounds found in biological systems
• Either hydrophobic (non-polar) or amphipathic
  (polar and non-polar regions)
• Types of lipids for domestic industrial
  purposes
• Oils, margarine butter, dripping, lard,
  shortening, tallow, waxes
• General characteristics
• Oily greasy feel (leaves greasy spot on filter
  paper)
• Not easily mix with water (float on water)
• Dispersed in detergent, hot water or alcohol

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2. Classification

• Origin
• Animal
• Mammal depot fat (lard, tallow), milk fat
  (ruminant), marine (fish oil)
• Marine eicosapentanoic (EPA), docosahexaenoic
  (DHA) in tuna, sardines mostly unsaturated
  biomedical advantages for human body
• Veg
• Seed oils (canola), fruit coats (olive oil),
  kernel oils (coconut oil)
• Visible / invisible
• Visible lard, butter, margarine, shortening,
  cooking oils
• Invisible fat in eggs, meat, poultry, fruits,
  veg, grain
• Based on melting point
• Fats solid / semisolid _at_ room temp (usually
  animal origin - margarine)
• Oils liquid (melting point) below room temp
  (usually plant origin - sunflower oil)

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2. Classification

• Based on structure

Basic lipid components
Quantitative
Phospholipids
Hexoses Sphingosine Sterols Glyserol Fatty
acids Fatty alcohols Phosphoric acid amino
alcohols Fatty aldehydes
Sterol esters Mono-, di-, tri glyserides
Cerebrosides Sphingomyelin Phosphatidyl
esters Plasmalogens
Glyceryl ether
Waxes
Ether esters
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3. Fatty acids

• Simplest lipids fatty acids, formula R-COOH (R
  is a hydrocarbon chain, COOH is a carboxyl
  functional group)
• Fatty acids differ from each other by
• Length of hydrocarbon tail
• Degree of unsaturation (no. of double bonds)
• Sat. are waxy at room temp.
• Unsat. Are liquid at room temp.
• Less double bonds, longer carbon tail ? higher
  melting temp
• Positions of double bonds
• Essentiality essential fatty acids (e.g. oleic,
  linoleic, linolenic) not produced by body, only
  from plant origin usually unsaturated
• Common names for frequently used fatty acids
• IUPAC naming
• Carboxyl carbon named C-1, remaining carbons
  named sequentially
• Carbon adjacent to carboxyl named , rest
  also followed by greek letters ( refers to
  carbon farthest from carboxyl group)
• No carbon-carbon double bond saturated, at
  least 1 double bond - unsaturated

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3. Fatty acids

• IUPAC naming
• 1 double bond monounsaturated, 2/more double
  bonds polyunsaturated
• Positions of double bonds indicated by ?n (n
  indicates the lower-numbered carbon of each
  double bond
• Shorthand notation uses 2 numbers seperated by
  colon, e.g. arachidonate

Eicosatetraenoate
No. of C-atoms in fatty acid
204 ?5,8,11,14
Common name
Double bond positions
No. of C-C double bonds
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3. Fatty acids

• NB draw structures if IUPAC name is given,
  Tables 2.2, 2.3, p37-38
• 2 types of double bonds
• Cis Hydrogens on same side of bond causes
  bending of hydrocarbon chains
• Bending prevents close packing of hydrocarbons ?
  cis unsaturated fats lower melting point
• Trans Hydrogens on opposite sides of bond -
  mostly saturated fats higher melting point
  more stable
• Draw structures indicating difference between cis
  trans!

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4. Gliserides

• A 3-carbon alcohol usually combines with fatty
  acids (esterification)
• Glyseride also neutral lipid do not carry any
  charge
• When 1 carbon is esterified with fatty acid ?
  monogliseride, when 2 Cs esterified with fatty
  acid ? digliseride, etc.
• Glyserol has plane of symmetry (2 of 4
  constituents around central carbon is identical)
  - monogliserides 2 structures enantiomeres
  (chiral) (Fig. 2.7, p. 47)
• Saponification number the reaction of a product
  with a weak acid / base
• The basis of the soap-making industry
• Saponification number (S.N.) index of degree of
  esterification
• The higher the degree of esterification, the
  higher the S.N.
• Used as quality control tool in oils fats
  industry
• Lipids that do not have gliserides will not
  saponify
• Lipids can thus also be classified into
  saponifiable and non-saponifiable

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4. Gliserides

• Hydrogenation Chemical reaction by addition of
  hydrogen to double bonds of unsaturated acyl
  groups
• For conversion of oils to fats (e.g. production
  of margarine
• Results in a decreased susceptibility to
  oxidative deterioration
• Reaction gaseous hydrogen liquid oil solid
  catalyst (Ni) react under agitation in closed
  vessel
• Hydrogenation not usually completed
• May be selective (H2 added first to most
  unsaturated fatty acid) or non-selective
• Selectivity increased by increasing hydrogenation
  temp
• Iodine number reaction of iodine with double
  bonds
• Amount of iodine used indicates the amount of
  unsaturation remaining

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5. Phospholipids

• Present in animal fats (lard, beef tallow), crude
  vegetable oils (cottonseed, corn, soybean oil),
  fish
• Can be removed from fats oils by refining,
  neutralization, bleaching, deoderization ? oil
  free from phospholipid
• Phospholipid removed from soybean oil used as
  emulsifier (in chocolates!)
• Carry a charged group
• Components
• Diglyseride (fatty acids of diglyseride can vary
  in different sources)
• Esterified to phosphate group (derived from
  strong acid - H3PO4)
• Esterified to a nitrogen-containing base
  (choline, inositol, ethanolamine, serine)
• Draw structures of phosphatidylcholine (lecitin),
  phosphatidylethanolamine (cephalin),
  phosphatidylserine, phosphoinesitides (p. 52)
• Amphipathic
• Hydrophobic (lipophilic) portion (tail) - due to
  long fatty acid tails of diglyseride
• Hydrophilic portion (head) - due to charged base
  phosphate also partially charged

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6. Unsaponifiables

• Unsaponifiable fractions in fats are
• Sterols (most NB)
• phytosterol in plants cholesterol in animals
• Solids with high melting points
• Flat molecules with all trans bonds
• Are compounds containing perihydrocyclo-penteno-ph
  enanthrene nucleus rings
• Cholesterol structure (fig. 2.12, p. 54)
• Also terpenic alcohols, aliphatic alcohols,
  squaline, hydrocarbons

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7. Emulsions emulsifiers

• Emulsion a heterogeneous system consisting of
  one immiscible liquid intimately dispersed in
  another one, in the form of droplets with
  diameter over 0.1µm (milk, salad dressing)
• Usually 2 phases oil water
• If water continuous phase oil dispersed phase
  oil-in-water (O/W) type
• If reversed W/O type
• Most common - phospholipids
• Emulsifiers
• surface agents that give stability to emulsions
• Reduce interfacial tension between air-liquid
  liquid-liquid interfaces
• Due to molecular structure contain hydrophilic
  (polar) hydrophobic (non-polar) properties
• Action of emulsifiers enhanced by stabilizers
• Macromolecules e.g. starch proteins
• HLB system numerical value for relative
  simultaneous attraction of emulsifier for water
  oil (e.g. low HLB tend to form W/O emulsions)
• Additional functions modify physical
  characteristics of potato products, pasta,
  antifirming effect to improve shelf life of bread

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8. Physical properties of oils fats

• Oils fats mixtures of triglyserides
• Fats semisolid at room temp plastic fats
• Solid characteristic is result of presence of
  some crystallized triglyserides
• Fats have range of triglyserides at different
  melting points
• Fat liquifies upon heating (all triglyserides in
  liquid state)
• Upon cooling - higher melting fractions become
  crystallized, insoluble - ? in solid fat content

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8. Physical properties of oils fats

• Above changes used to determine
• melting point
• Affected by chain length, unsaturation,
  configuration around double bond
• solidification temp,
• solid fat content
• Dependent on temperature
• Measure with dilatometer by melting expansion of
  fats upon heating gives approximation of solid
  fats contents reported as SFI
• Lately measure with NMR (nuclear magnetic
  resonance) gives true solid fat contents
  reported as SFC
• (Look at Fig. 2.39, p. 85)
• Cooling
• Slow cooling nucleation min, large crystals
  form
• Supercooling nucleation high, small / mixed
  crystals form
• Fats do not form a glassy state like water does!
• Crystal size - 0.1-0.5µm, sometimes 50µm
• large crystals are grainy, 3 dim. Network, giving
  rigidity to product, holds the liquid portion of
  the fat

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8. Physical properties of oils fats

• Polymorphism
• Existence of more than 1 crystal form ( ,
  , )
• Cause different patterns of molecular packing
  in fat crystals
• Plastic range of fats
• in a relationship between SFC and hardness, there
  is narrow range of solids that results in a
  product that neither too hard nor too soft, e.g.
  shortening (requires extended plastic range)

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9. Cocoa butter

• Natural fat with unusual physical properties
• High content of monounsaturated triglyserides
• 3 major fatty acids palmitic, oleic, stearic
• Chocolate has desirable snap, glossy, melt
  smoothly in mouth, no greasiness on palate
• High SFC at room temp, steep decline as temp
  reaches human body temp ? al liquified, no
  waxiness
• Special tempering procedure needed to produce
  desired polymorphic form
• 50-60C for 1h ? cool to 25-27C, to initiate
  crystallization ? heat to 29-31C ? cool to
  5-10C
• After long storage / extreme temperatures
  chocolate shows bloom greyish covering on
  surface (unsuitable for consumption) caused by
  most stale crystal
• Confectionary / specialty fats can replace cocoa
  butter CBSs CBIs

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10. Heated fats - frying

• Heating during processing (120-270C) involve
  hydrogenation, physical refining, deodorization
• Changes
• Randomization of glyseride structure
• Dimer formation
• Cis-trans isomerization
• Formation of conjugated fatty acids of
  polyunsaturated fatty acids
• No air contact, thus no oxidization
• Deep frying (food heated by immersion in hot oil)
  _at_ 160-195C
• Lower temp ? takes too long food takes up too
  much oil
• High temp ? oil deterioration (food oil being
  fried)

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10. Heated fats - frying

• (NB - Fig. 2.23, p. 68 / notes!)
• Steam given off remove volatile antioxidants,
  free fatty acids, other volatiles
• Presence of steam hydrolysis ? produce free
  fatty acids partial glyserides
• Air contact autooxidation, formation of
  degradation products (free radical proxide
  mechanism
• Lipid soluble colour components of food lipids
  leach into the frying oil
• Final products aldehydes, alcohols, ketones,
  which eventually polimerise
• Suitability of fat for frying depends on
  inherent stability
• Calculated from level of unsaturated fatty acids
  relative reaction rate with O2
• The higher the inherent stability, the less
  suitable for frying
• Oils used for deep frying must be of high quality
• Harsh conditions during frying
• Must provide long shelf life of product