Measurement of Lipids

Contents

1. Introduction (definition ,characteristics)

2. Function of lipids in foods

3. Determination of fats in food

4. Quality evaluation of edible oils

IntroductionLipids1) The term lipid is used to denote fats and fatlike subst

ances and is synonymous with the terms lipoids or lipins.

2) It includes a great varieties. The main component is triglycerides(>95%), others include phospholipids, wax, fatty acids, cholesterin etc.

3) Lipids are usually defined as food components that are insoluble in water but soluble in organic solvents.

4) 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).

Characteristics of lipids

1. Insoluble in water, but soluble in organic solvents , such as ethyl oxide( 乙醚 ),petroleum ether( 石油醚 ), chloroform( 氯仿 ),acetone ( 丙酮 ).

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( 磷脂 ), sphingomyelin( 鞘磷脂 ), etc.

Function of lipids in foods

1.Provide caloric.2. Provide essential fatty acids(linolenic acid 亚麻

酸 , linoleic acid 亚油酸 )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.

Determination of fats in food

Soxhlet extractor method

Extraction of crude fats ethyl ether in acid( 酸性乙醚提取法）

Extraction of crude fats by ethyl ether in

Alkali ( 碱性乙醚提取法）（罗兹－哥特里法）

Babcock Method and Gerber method( 巴布科氏法和盖勃氏法 )

Extraction of fats by Chloroform-Methanol ( 氯仿－甲醇抽提法）

索氏提取法

样品 粗脂肪蒸去溶剂乙醚或石油醚

Principle

Procedure:

1)Preparation of sample:

Solid sample –grinding

Semi-solid sample or liquid sample– adding sand– dried—grinding

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

Attention

1) Crude fats include : phospholipids, pigments,wax, volatile oil, etc.

2) Sample should contain greater amount of free fats, little associated fats.

3) Samples should be dried(decrease the efficiency, increase nonfat substance)

4) If more dextrin or saccharide is included in sample, it should be remove by water

5) Ethyl ether should be purified: no water, no peroxide, no alcohol.

6) It should be heated in water bath, be careful of firing.

Determination of fats in food

Soxhlet extractor method

sample Crude fatDistill Ethyl ether or

Petroleum ether

Principle

Extraction of crude fats ethyl ether in acid( 酸性乙醚提取法）

Principle: sample +HCl +H2O released associa

ted fats to exist in the free form. Hydrolyzed sample +ethanol +ethyl ether +petroleum

ether Crude fats Recycle solvents, and weight

Hydrolysis by heating

Extract

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

Attention: sample without high saccharides and phospholipids Sample include: liquid sample, semi-solid sample, sa

mple 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 emulsio

n, promote fats together, and solute carbonhydrates. Addition of petroleum ether can decrease the solubiltiy

of ethanol in ethyl ether, and favorable for phase separation.

Extraction of crude fats by ethyl ether in alkali( 碱性乙醚提取法）（罗兹－哥特里法）

PrincipleSample + NH3.H2O+ ethanol Hydrolysis Released associated fats in foods

Hydrolyzed sample +ethyl ether +petroleum ether extract fats

Recycle solvents, dried, and weighting

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,.

Attention The method is used in the determination of fats in the milk prod

uct

NH3.H2O can destroy the colloidal medium( 胶体介质） and the membrane of fat globule （脂肪球） .

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

Babcock Method and Gerber method( 巴布科氏法和盖勃氏法 )

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

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.

Extraction of fats by Chloroform-Methanol ( 氯仿－甲醇抽提法）

Principle

Chloroform-Methanol associated fatsFree fats

Sample filter

Recycle solvents,adding petroleum ether extract

Distill the petroleum ether, weighting

Attention Suitable for sample with high associated

fats, especially phospholipids. Such as fish,eggs, meat etc.

for dried sample, some water should be added.

Fractionation of extracted lipids

TLC : one of the main analytical tools in lipid research and analysis.

Column Chromatography:if 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

Quality evaluation of oil and fats

1. Transparency( 透明度 )

2. Color( 色泽 )

3. Odour( 气味 )

4. Taste( 滋味 )

5. Relative density( 相对密度 )

6. Refractive Index( 折射率 )

7. Smoke point( 烟点 )

8. Melting point( 熔点 )

9. Freezing point( 凝固点 )

10.Determination of impurity( 杂质测定 )

11.Determination of acid value( 酸价测定 )

12. Determination of phospholipids( 磷脂测定 )

13.Determination of soap ( 含皂量测定 )

14.Determination of saponification value( 皂化价的定 )

15.Determination of unsaponifiable matter( 不皂化物测定 )

16. Determination of iodine value( 碘价测定 )

17.Determination of peroxide value( 过氧化值测定 )

18.Determination of carbonyl value ( 羰基价测定 )

1) 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 cylinder—kept 20 for 24h—observe under incandescent ℃light—transparent or not

3) if the oil sample is cool, it must be heated to 50 , and then cooled to 20 to observe.℃ ℃

Transparency(透明度 )

1) Color is a important indicator of edible oil.

2) Determination

Chromometer

Color (色泽 )

1) Different oil have their special odour and taste.

2) Determination:

oil sample in beaker—heat to 50 --stirring – s℃mell and degust

Odour( 气味 ) and Taste( 滋味 )

1) Relative density and refractive Index is physical characteristics of oil.

2) Determination

it can analyzed by densitometer and Abbe refractometer.

Relative density( 相对密度 ) and Refractive Index( 折射率 )

DefinitionThe temperature when the smoke produce firstly.

Smoke point is a indicator of oil stability in the air.

• Determination

apparatus for determining smoke point

Smoke point( 烟点 )

Melting point( 熔点 )

Definition Temperature when solid fats were transformed to l

iquid.

2) Fats sample in a water bath with heat indicator—heat (0.5 /min)– transparent liquid –record ℃the temperature

Freezing point( 凝固点 )

Oil freezing process Temperature when liquid oil was transformed t

o solid. It is kept at some point for a little wile. Determination

Oil sample- saponification-- fatty acids-- dry at 130 --freezing point determination℃

Determination of impurity( 杂质测定 )

Definition

Residuals that are insoluble in organic solvents, such as petroleum ether. They are earth, sandstone, etc.

DeterminationDissolve samples in the petroleum ether—filter –

separation of impurity and oil—dry impurity –weighting

Determination of acid value( 酸价测定 )

DefinitionAmount (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 ether—titrate the free fatty acids with alkali – calculate the alkali consumed.

Determination of phospholipids( 磷脂测定 )

Structure

Characteristic

Effect on oil quality

Determination

• 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.

Determination

Principle

Phopholipids +H2O

precipitation

Washing precipitation with Acetone

Collecting precipitation

centrifugation

Dry and weighting

Determination of soap ( 含皂量测定 )

DefinitionSoap remained in the oil after oil refined. It was produced

by water washing incompletely.

Determination

1) Principles

titrate soap in the oil with strong acid.

2) Procedure

Sample—ethanol + petroleum ether—adding hot water(80 ),indicator—adding acid drop by drop—℃record the amount of acid consumed--calculation

Determination of saponification value( 皂化价的定 )

DefinitionAmount of KOH(mg) that needed in the saponifying 1

g of oil.

Determination

Oil + KOH—glycerol + soap,

use HCl to titrate the excessive KOH

calculate the consumed KOH

Determination of unsaponifiable matter( 不皂化物测定 )

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 ether—dry -weighting

Determination of iodine value( 碘价测定 )

DefinitionAmount of iodine (g) that 100g of oil can absorbed.

Determination CH3…CH2=CH2-COOH + ICl - …CHI-CHCl… Excessive KI was added to act with residual ICl, KI + ICl =KCl +I2 I2 was titrated by Na2S2O3

I2 + 2Na2S2O3—Na2S4O6 +2NaI

Determination of peroxide value( 过氧化值测定 )

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.

Determination of carbonyl value ( 羰基价测定 )

Definition all amount of Aldehyde and ketone; Mmol /kg oil

Determination

Carbonyl substances +DNP-hydrozine( 苯肼） – hydrazone( 腙） + OH- quinone( 醌 ) --440nm red color

谢谢