Lipids Lipids Main functions of lipids in foods Energy and

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Lipids
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Lipids

• Main functions of lipids in foods
• Energy and maintain human health
• Influence on food flavor
• Fatty acids impart flavor
• Lipids carry flavors/nutrients
• Influence on food texture
• Solids or liquids at room temperature
• Change with changing temperature
• Participation in emulsions

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Lipids

• Lipids are soluble in many organic solvents
• Ethers (n-alkanes)
• Alcohols
• Benzene
• DMSO (dimethyl sulfoxide)
• They are generally NOT soluble in water
• C, H, O and sometimes P, N, S

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Lipids

• Neutral Lipids
• Triacylglycerols
• Waxes
• Long-chain alcohols (20 carbons in length)
• Cholesterol esters
• Vitamin A esters
• Vitamin D esters
• Conjugated Lipids
• Phospholipids, glycolipids, sulfolipids
• Derived Lipids
• Fatty acids, fatty alcohols/aldehydes,
  hydrocarbons
• Fat-soluble vitamins

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Lipids

• Structure
• Triglycerides or triacylglycerols
• Glycerol 3 fatty acids
• gt20 different fatty acids

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Lipids 101-What are we talking about?

• Fatty acids- the building block of fats
• A fat with no double bonds in its structure is
  said to be saturated (with hydrogen)
• Fats with double bonds are referred to as mono-,
  di-, or tri- Unsaturated, referring to the number
  of double bonds. Some fish oils may have 4 or 5
  double bonds (polyunsat).
• Fats are named based on carbon number and number
  of double bonds (160, 161, 182 etc)

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Lipids

• Oil- liquid triacylglycerides Oleins
• Fat- solid or semi-solid mixtures of crystalline
  and liquid TAGs Stearins
• Lipid content, physical properties, and
  preservation are all highly important areas for
  food research, analysis, and product development.
• Many preservation and packaging schemes are aimed
  at prevention of lipid oxidation.

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Nomenclature

• The first letter C represents Carbon
• The number after C and before the colon indicates
  the Number of Carbon
• The letter after the colon shows the Number of
  Double Bond
• The letter n (or w) and the last number indicate
  the Position of the Double Bonds

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Saturated Fatty Acids
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Mono-Unsaturated Fatty Acids
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Poly-Unsaturated Fatty Acids
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Lipids

• Properties depend on structure
• Length of fatty acids ( of carbons)
• Position of fatty acids (1st, 2nd, 3rd)
• Degree of unsaturation
• Double bonds tend to make them a liquid oil
• Hydrogenation tends to make a solid fat
• Unsaturated fats oxidize faster
• Preventing lipid oxidation is a constant battle
  in the food industry

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Lipids 101-What are we talking about?

• Fatty acid profile- quantitative determination of
  the amount and type of fatty acids present
  following hydrolysis.
• To help orient ourselves, we start counting the
  number of carbons starting with 1 at the
  carboxylic acid end.

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Lipids 101-What are we talking about?

• For the 18-series (180, 181, 182, 183) the
  double bonds are usually located between carbons
  910 1213 1516.

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Lipids 101-What are we talking about?

• The biomedical field entered the picture and
  ruined what food scientists have been doing for
  years with the OMEGA (w) system (or n fatty
  acids).
• With this system, you count just the opposite.
• Begin counting with the methyl end
• Now the 1516 double bond is a 34 double bond or
  as the medical folks call it.an w-3 fatty acid

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Lipids

• Properties depend on structure
• Length of fatty acids ( of carbons)
• Position of fatty acids (1st, 2nd, 3rd)
• Degree of unsaturation
• Double bonds tend to make them a liquid oil
• Hydrogenation tends to make a solid fat
• Unsaturated fats oxidize faster
• Preventing lipid oxidation is a constant battle
  in the food industry

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Melting Points of Lipids
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Tuning Fork Analogy-TAGs

• Envision a Triacylglyceride as a loosely-jointed
  E
• Now, pick up the compound by the middle chain,
  allowing the bottom chain to hang downward in a
  straight line.
• The top chain will then curve forward and form an
  h
• Thus the tuning fork shape
• Fats will tilt and twist to the lowest free
  energy level

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Lipids

• Lipids are categorized into two broad classes.
• The first, simple lipids, upon hydrolysis, yield
  up to two types of primary products, i.e., a
  glycerol molecule and fatty acid(s).
• The other, complex lipids, yields three or more
  primary hydrolysis products.
• Most complex lipids are either glycerophospholipid
  s, or simply phospholipids
• contain a polar phosphorus moiety and a glycerol
  backbone
• or glycolipids, which contain a polar
  carbohydrate moiety instead of phosphorus.

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Lipids
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A Common other Lipid

• Phospholipids
• Structure similar to triacylglycerol
• High in vegetable oil
• Egg yolks
• Act as emulsifiers

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Fats and Oilscan also be convertedto an
emulsifier

• Production of mono- and diglycerides
• Use as Emulsifiers
• Heat fat or oil to 200C
• Add glycerol and alkali
• Free Fatty Acids will be added to the glycerol

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Oil Extraction
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Where Do We Get Fats and Oils?

• Crude fats and oils are derived from plant and
  animal sources
• Several commercial processes exist to extract
  food grade oils
• Most can not be used without first refining
  before they reach consumers
• During oil refining, water, carbohydrates,
  proteins, pigments, phospholipids, and free fatty
  acids are removed. 
• Crude fats and oils can therefore be converted
  into high quality edible oils
• In general, fat and oil undergo four processing
  steps
• Extraction
• Neutralization
• Bleaching
• Deodorization
• Oilseeds, nuts, olives, beef tallow, fish skins,
  etc.
• Rendering, mechanical pressing, and solvent
  extraction.

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Fats and Oils Processing
Peanut

• Extraction
• Rendering
• Pressing oilseeds
• Solvent extraction

Rape Seed
Safflower
Sesame
Soybean
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Fats and OilsFurther Processing

• Degumming
• Remove phospholipids with water
• Refining
• Remove free fatty acids (alkali water)
• Bleaching
• Remove pigments (charcoal filters)
• Deodorization
• Remove off-odors (steam, vacuum)

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Where Do We Get Fats and Oils?

• Rendering
• Primarily for extracting oils from animal
  tissues. 
• Oil-bearing tissues are chopped into small pieces
  and boiled in water. 
• The oil floats to the surface of the water and
  skimmed. 
• Water, carbohydrates, proteins, and phospholipids
  remain in the aqueous phase and are removed from
  the oil. 
• Degumming may be performed to remove excess
  phospholipids.
• Remaining proteins are often used as animal feeds
  or fertilizers.

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Where Do We Get Fats and Oils?

• Mechanical Pressing
• Mechanical pressing is often used to extract oil
  from seeds and nuts with oil gt50. 
• Prior to pressing, seed kernels or meats are
  ground into small sized to rupture cellular
  structures. 
• The coarse meal is then heated (optional) and
  pressed in hydraulic or screw presses to extract
  the oil.
• Olive oils is commonly cold pressed to get virgin
  or extra virgin olive oil. It contains the least
  amount of impurities and is often edible without
  further processing.
• Some oilseeds are first pressed or placed into a
  screw-press to remove a large proportion of the
  oil before solvent extraction.

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Where Do We Get Fats and Oils?

• Solvent Extraction
• Organic solvents such as petroleum ether, hexane,
  and 2-propanol can be added to ground or flaked
  oilseeds to recover oil. 
• The solvent is separated from the meal, and
  evaporated from the oil.
• Neutralization
• Free fatty acids, phospholipids, pigments, and
  waxes exist in the crude oil
• These promote lipid oxidation and off-flavors
• Removed by heating fats and adding caustic soda
  (sodium hydroxide) or soda ash (sodium
  carbonate). 
• Impurities settle to the bottom and are drawn
  off. 
• The refined oils are lighter in color, less
  viscous, and more susceptible to oxidation.
• Bleaching
• The removal of color materials in the oil.
• Heated oil can be treated with diatomaceous
  earth, activated carbon, or activated clays.
• Colored impurities include chlorophyll and
  carotenoids
• Bleaching can promote lipid oxidation since some
  natural antioxidants are removed.

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Where Do We Get Fats and Oils?

• Deodorization
• Deodorization is the final step in the refining
  of oils.
• Steam distillation under reduced pressure
  (vacuum).
• Conducted at high temperatures of 235 - 250ºC.
• Volatile compounds with undesirable odors and
  tastes can be removed.
• The resultant oil is referred to as "refined" and
  is ready to be consumed.
• About 0.01 citric acid may be added to
  inactivate pro-oxidant metals.

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Fats and OilsFurther Processing

• Hydrogenation
• Add hydrogen to an oil to saturate the fatty
  acid double bonds
• Conducted with heated oil
• Often under pressure
• In the presence of a catalyst (usually nickel)
• Converts liquid oils to solid fats
• Raises melting point

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Hydrogenating Vegetable Oils

• Trans-unsaturated fatty acids may be found in
  hydrogenated vegetable oils. 
• Oils are hydrogenated to improve oxidation
  stability and to increase melting point. 
• Oils becomes a solid at room temperature.
• During hydrogenation, some unsaturated fatty
  acids that are normally in the cis configuration
  are converted to the trans isomers. 
• The resulting trans-fatty acids have biological
  properties similar to those of saturated fatty
  acids.
• Increased blood lipids, increased LDL
  cholesterol, and decreased HDL cholesterol.
• Prompted food package labeling change in 2006

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Hydrogenating Vegetable oils may produce
trans-fats
Cis-
Trans-
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The cis- and trans- forms of a fatty acid
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Fats and OilsMelting and Texture

• Think of a fat as a crystal, that when heated
  will melt.
• Length of fatty acid chain
• Short chains have low melting points
• Oils vs soft fats vs hard fats
• Degree of unsaturation
• Unsaturation presence of double bonds
• Unsaturation low melting point

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Fats and Oils in Foods

• SOLID FATS are made up of microscopic fat
  crystals. Many fats are considered semi-solid, or
  plastic.
• PLASTICITY is a term to describe a fats softness
  or the temperature range over which it remains a
  solid.
• PLASTIC FATS are a 2 phase system
• Solid phase (the fat crystals)
• Liquid phase (the oil surrounding the crystals).
• Plasticity is a result of the ratio of solid to
  liquid components.
• Plasticity ratio volume of crystals / volume of
  oil
• Measured by a solid fat index or amount of
  solid fat or liquid oil in a lipid
• As the temperature of a plastic fat increases the
  fat crystals melt and the fat will soften and
  eventually turn to a liquid.
• Even a fat that appears liquid at room
  temperature contains a small number of
  microscopic solid fat crystals suspended in the
  oil..and vice versa

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Shortening

• Plastic range
• Temperature range over which it is solid (melting
  point)
• Want a large plastic range for shortening
• Want it to remain a solid at high temps.
• Holding air during baking

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Frying Oils

• Want a short plastic range
• Liquid or low melting point
• Do not want mono- or diglycerides or oil will
  smoke when heated
• Must be stable to oxidation, darkening
• Methyl silicone may be added to help reduce
  foaming

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Fat and Oil Further Processing

• Winterizing
• Cooling a lipid to precipitate solid fat crystals
• DIFFERENT from hydrogenation
• Plasticizing
• Modifying fats by melting (heating) and
  solidifying (cooling)
• Tempering
• Holding the fat at a low temperature for several
  hours to several days to alter fat crystal
  properties
• (Fat will hold more air, emulsify better, and
  have a more consistent melting point)

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Fat Crystals a, ß, ß

• The proportion of fat crystals to oil also
  depends on the melting points of the crystals.
• Most fats exhibit polymorphism, meaning they can
  exist in one of several crystal forms. These
  crystal forms are 3-D arrangements.
• Three primary crystal forms exist
• a-form (not very dense, lowest melting point),
  unstable
• ß-form (moderate density, moderate melting
  point), not as stable
• ß-form (most dense, highest melting point), very
  stable
• Rapid cooling of a heated fat will result in fine
  a crystals.
• Slow cooling favors formation of the coarse ß
  crystals.
• Fat crystals are easily observed when
  butter/shortening is melted and allowed to
  re-solidify.

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Fat Crystals in Commercial Oilsa, ß, ß

• Crystal forms are largely dependent on the fatty
  acid composition of the lipid
• Monoacid lipids (3 of the same fatty acids)
• Mixed lipids or heterogeneous lipids (different
  FAs)
• Some fats will only solidify to the ß-form
• Soybean, peanut, corn, olive, coconut, cocoa
  butter, etc
• Other fats will harden to the ß-form
• Cottonseed, palm, canola, milk fat, and beef
  tallow
• ß forms are good for baked goods, where a high
  plastic range is desired

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Chocolate Bloom

• In chocolate (cocoa butter), the desired stable
  crystal form is the ß-form
• Processing involves conching (blending cocoa and
  sugar to a super-fine particle) and
• Tempering (heating/cooling steps).
• Together, these give ß crystals to the final
  chocolate
• Fine chocolates control this well.

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Chocolate

• Making chocolate
• The polymorphs of chocolate affect quality and
  keeping quality.
• When making chocolate, the tempering process
  alters the fat crystals and transforms to a
  predominance of ß-forms.
• This process begins with the formation of some ß
  crystals as seeds from which additional
  crystals form.
• The chocolate is then heated to just below the
  temperature for ß-forms to melt (thus melting all
  other forms), and allows the remaining fats to
  crystalize into ß-forms upon cooling.
• Chocolate Bloom
• When chocolate has been heated and cooled, fat
  and sugar can rise to the surface, and change
  crystalline state (fat) or crystallize (sugar).
• When melted fat re-cools, less stable and lower
  melting point a crystals can form.
• The different crystals also physically look
  different (white, grey, etc) against the brown
  background of the chocolate bar.