Measurement of Lipids

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Measurement of Lipids
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Contents

1. Introduction (definition ,characteristics)
2. Function of lipids in foods
3. Determination of fats in food
4. Quality evaluation of edible oils

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Introduction

• Lipids
• The term lipid is used to denote fats and fatlike
  substances and is synonymous with the terms
  lipoids or lipins.
• It includes a great varieties. The main component
  is triglycerides(gt95), others include
  phospholipids, wax, fatty acids, cholesterin etc.
• Lipids are usually defined as food components
  that are insoluble in water but soluble in
  organic solvents.
• Essential structural component of living cells
  (along with proteins and carbohydrates).
• 5) exist in the free form(such as fats or oil),or
  associated ( combined with carbohydrates,or
  protein in food).

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Characteristics of lipids

1. Insoluble in water, but soluble in organic
   solvents , such as ethyl oxide(??),petroleum
   ether(???), chloroform(??),acetone (??).
2. Most of lipids contain ester bond, and main
   section is fatty acid ester.
3. Be produced by organism, and can be used by
   organism(different from mineral oil).
4. Except the phospholipids(??), sphingomyelin(???),
   etc.

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Function of lipids in foods

• 1.Provide caloric.
• 2. Provide essential fatty acids(linolenic
  acid???, linoleic acid???)
• 3.Carrier of fat-soluble vitamin(VE,VA,VD)
• 4. Provide glossy appearance, smooth taste.
• 5. Provide savory in the fry food.
• Lipids content is one of indexes of evaluating
  food quality , and food nutrition, food
  processing and storage.

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Determination of fats in food

• Soxhlet extractor method
• Extraction of crude fats ethyl ether in
  acid(???????)
• Extraction of crude fats by ethyl ether in
• Alkali (???????)(??-????)
• Babcock Method and Gerber method(??????????)
• Extraction of fats by Chloroform-Methanol
  (??-?????)

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Principle
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• Procedure
• 1)Preparation of sample
• Solid sample grinding
• Semi-solid sample or liquid sample adding
  sand driedgrinding
• 2) Preparation of filter paper tube
• 3) Put sample ready into the filter paper tube.
• 4) Extract the fats with solvents
• 5) Weighting
• 6) Calculation

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• Attention
• Crude fats include phospholipids, pigments,wax,
  volatile oil, etc.
• Sample should contain greater amount of free
  fats, little associated fats.
• Samples should be dried(decrease the efficiency,
  increase nonfat substance)
• If more dextrin or saccharide is included in
  sample, it should be remove by water
• Ethyl ether should be purified no water, no
  peroxide, no alcohol.
• It should be heated in water bath, be careful of
  firing.

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Determination of fats in food

• Soxhlet extractor method

Principle
Distill
sample
Crude fat
Ethyl ether or Petroleum ether
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• Extraction of crude fats ethyl ether in
  acid(???????)
• Principle
• sample HCl H2O
  released associated fats to exist in the free
  form.
• Hydrolyzed sample ethanol ethyl ether
  petroleum ether Crude fats
• Recycle solvents, and weight

Hydrolysis by heating
Extract
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• Procedure
• Sample preparation
• Hydrolysis
• heating at 70-80? in a water bath for 40-50min
• Extract
• ethanol , ethyl ether, petroleum ether,
• Weighting
• Calculating

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• Attention
• sample without high saccharides and
  phospholipids
• Sample include liquid sample, semi-solid sample,
  sample difficult to be dried, and sample that can
  not to be analyzed by soxhlet extractor.
• It can determine the associated fats in foods.
• ethanol can make protein precipitated, retard
  emulsion, promote fats together, and solute
  carbonhydrates.
• Addition of petroleum ether can decrease the
  solubiltiy of ethanol in ethyl ether, and
  favorable for phase separation.

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• Extraction of crude fats by ethyl ether in
  alkali(???????)(??-????)

Principle
Hydrolysis

• Sample NH3.H2O ethanol

Released associated fats in foods
extract

• Hydrolyzed sample ethyl ether petroleum ether

fats

• Recycle solvents, dried, and weighting

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• Procedure
• Adding NH3.H2O into sample, mixed, and heated for
  5min in a 60? water bath.
• Adding ethanol to reaction system, mixed and
  cooled.
• Extraction with ethyl ether and petroleum ether.
• Recycle solvents ,dried at 100-105?, and
  weighting,.

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• Attention
• The method is used in the determination of fats
  in the milk product
• NH3.H2O can destroy the colloidal medium(????)
  and the membrane of fat globule(???).
• ethanol can make protein precipitated, and
  retard emulsion, and solute the alcohol soluble
  substances.
• Addition of petroleum ether can decrease the
  solubiltiy of ethanol in ethyl ether, and
  favorable for phase separation

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Babcock Method and Gerber method(??????????)

• Principle
• Milk product concentrated H2SO4 solute
  nonfat components in milk, destroy the member of
  fat globule and emulsion, release fats
  
• adipose layer was seperated
  record the volume of fats

Heat and centrifugate
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• Attention
• Control the concentration of H2SO4, if it is too
  high , the milk will be carbonized, if it is too
  low, the fat globule can not be destroyed
  completely.
• Sample without high saccharides and chocolate.

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Extraction of fats by Chloroform-Methanol
(??-?????)

• Principle

Chloroform-Methanol
filter
associated fats Free fats
Sample
extract
Recycle solvents,adding petroleum ether
Distill the petroleum ether,
weighting
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• Attention
• Suitable for sample with high associated fats,
  especially phospholipids. Such as fish,eggs, meat
  etc.
• for dried sample, some water should be added.

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Fractionation of extracted lipids

• TLC one of the main analytical tools in lipid
  research and analysis.
• Column Chromatographyif silicic acid column was
  selected,Neutral lipids, such as hydrocarbons,
  glycerides, sterols, and sterol esters, are
  eluted with chloroform, the remaining polar
  lipids are eluted with methanol.
• GC fatty acid compositions in the oils and fats
• HPLC different components in the mixed lipids

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Quality evaluation of oil and fats
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1. Transparency(???)
2. Color(??)
3. Odour(??)
4. Taste(??)
5. Relative density(????)
6. Refractive Index(???)
7. Smoke point(??)
8. Melting point(??)
9. Freezing point(???)

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• 10.Determination of impurity(????)
• 11.Determination of acid value(????)
• 12. Determination of phospholipids(????)
• 13.Determination of soap (?????)
• 14.Determination of saponification value(?????)
• 15.Determination of unsaponifiable matter(??????)
• 16. Determination of iodine value(????)
• 17.Determination of peroxide value(??????)
• 18.Determination of carbonyl value (?????)

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Transparency(???)

• Observe the transparency of oil sample under
  incandescent light when sample was kept at a
  definite temperature for a definite time.
• 2) determination
• Oil sample in 100ml colorimetric cylinderkept
  20? for 24hobserve under incandescent
  lighttransparent or not
• 3) if the oil sample is cool, it must be heated
  to 50?, and then cooled to 20? to observe.

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Color (??)

• Color is a important indicator of edible oil.
• Determination
• Chromometer

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Odour(??) and Taste(??)

• Different oil have their special odour and taste.
  
• Determination
• oil sample in beakerheat to 50?--stirring
  smell and degust

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Relative density(????) and Refractive Index(???)

• Relative density and refractive Index is
  physical characteristics of oil.
• Determination
• it can analyzed by densitometer and Abbe
  refractometer.

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Smoke point(??)

• Definition
• The temperature when the smoke produce firstly.
  Smoke point is a indicator of oil stability in
  the air.
• Determination
• apparatus for determining smoke point

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• Melting point(??)
• Definition
• Temperature when solid fats were transformed to
  liquid.
• 2) Fats sample in a water bath with heat
  indicatorheat (0.5?/min) transparent liquid
  record the temperature

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• Freezing point(???)
• Oil freezing process
• Temperature when liquid oil was transformed to
  solid. It is kept at some point for a little
  wile.
• Determination
• Oil sample- saponification-- fatty acids--
  dry at 130?--freezing point determination

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Determination of impurity(????)

• Definition
• Residuals that are insoluble in organic
  solvents, such as petroleum ether. They are
  earth, sandstone, etc.
• Determination
• Dissolve samples in the petroleum etherfilter
  separation of impurity and oildry impurity
  weighting

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Determination of acid value(????)

• Definition
• Amount (mg)of KOH that needed to consume the the
  quantity of free fatty acids in 1g of oil.
• Determination
• sample dissolved in ethanol and ethyl
  ethertitrate the free fatty acids with alkali
  calculate the alkali consumed.

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Determination of phospholipids(????)

• Structure

• Characteristic

• Effect on oil quality

• Determination

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• Charateristic
• Amphiphatic molecule
• Polarity
• Effect on oil quality
• Increase the water content because of its
  hydrophilic nature, and promote hydrolysis of
  oil.
• Easily be oxidized.
• Foam was produced when being heated.

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Determination
precipitation

• Principle

Washing precipitation with Acetone
centrifugation
Phopholipids H2O
Collecting precipitation
Dry and weighting
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Determination of soap (?????)

• Definition
• Soap remained in the oil after oil refined. It
  was produced by water washing incompletely.
• Determination
• Principles
• titrate soap in the oil with strong acid.
• 2) Procedure
• Sampleethanol petroleum etheradding hot
  water(80?),indicatoradding acid drop by
  droprecord the amount of acid consumed--calculati
  on

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Determination of saponification value(?????)

• Definition
• Amount of KOH(mg) that needed in the saponifying
  1g of oil.
• Determination
• Oil KOHglycerol soap,
• use HCl to titrate the excessive KOH
• calculate the consumed KOH

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Determination of unsaponifiable matter(??????)

• Definition
• Substances that can not be saponified.
• They includes pigments,vitamins, wax, sterol,
  etc.
• they are not dissolved in water, but soluble in
  ether.
• Determination
• Oil KOH--saponifying extract unsaponifiable
  matter with ethyl etherdry -weighting

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Determination of iodine value(????)

• Definition
• Amount of iodine (g) that 100g of oil can
  absorbed.
• Determination
• CH3CH2CH2-COOH ICl - CHI-CHCl
• Excessive KI was added to act with residual ICl,
• KI ICl KCl I2
• I2 was titrated by Na2S2O3
• I2 2Na2S2O3Na2S4O6 2NaI

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Determination of peroxide value(??????)

• Stale oil
• Hydrolysis( water, enzyme)fatty acids
• Oxidization (O2)acid,aldehyde,ketone, etc.
• Determination of peroxide value(mmol/kg)
• Peroxide can oxidize KI to produce free I2
• and then I2 was titrated by Na2S2O3,
• It was expressed as mmol O2/kg oil.

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Determination of carbonyl value (?????)

• Definition
• all amount of Aldehyde and ketone
• Mmol /kg oil
• Determination
• Carbonyl substances DNP-hydrozine(??)
  hydrazone(?) OH- quinone(? ) --440nm red
  color

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