Measurement of Lipids. Contents. Introduction (definition ,characteristics) Function of lipids in foods Determination of fats in food Quality evaluation of edible oils. Introduction. Lipids
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5) exist in the free form(such as fats or oil),or associated ( combined with carbohydrates,or protein in food).
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.
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
Soxhlet extractor method
Ethyl ether or
Hydrolysis by heating
heating at 70-80℃ in a water bath for 40-50min
ethanol , ethyl ether, petroleum ether,
Released associated fats in foods
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
Recycle solvents,adding petroleum ether
Distill the petroleum ether,
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
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)
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.
oil sample in beaker—heat to 50℃--stirring – smell and degust
Relative density(相对密度) and Refractive Index(折射率)
it can analyzed by densitometer and Abbe refractometer.
The temperature when the smoke produce firstly. Smoke point is a indicator of oil stability in the air.
apparatus for determining smoke point
Temperature when solid fats were transformed to liquid.
2) Fats sample in a water bath with heat indicator—heat (0.5℃/min)– transparent liquid –record the temperature
Oil sample- saponification-- fatty acids-- dry at 130℃--freezing point determination
Residuals that are insoluble in organic solvents, such as petroleum ether. They are earth, sandstone, etc.
Dissolve samples in the petroleum ether—filter –separation of impurity and oil—dry impurity –weighting
Amount (mg)of KOH that needed to consume thethe quantity of free fatty acids in 1g of oil.
sample dissolved in ethanol and ethyl ether—titrate the free fatty acids with alkali – calculate the alkali consumed.
Washing precipitation with Acetone
Dry and weighting
Soap remained in the oil after oil refined. It was produced by water washing incompletely.
titrate soap in the oil with strong acid.
Sample—ethanol + petroleum ether—adding hot water(80℃),indicator—adding acid drop by drop—record the amount of acid consumed--calculation
Amount of KOH(mg) that needed in the saponifying 1g of oil.
Oil + KOH—glycerol + soap,
use HCl to titrate the excessive KOH
calculate the consumed KOH
Oil +KOH--saponifying– extract unsaponifiable matter with ethyl ether—dry -weighting
Amount of iodine (g) that 100g of oil can absorbed.
KI + ICl =KCl +I2
I2 + 2Na2S2O3—Na2S4O6 +2NaI
Determination of peroxide value(mmol/kg)
and then I2 was titrated by Na2S2O3,
Carbonyl substances +DNP-hydrozine(苯肼） –hydrazone(腙） + OH- quinone(醌 ) --440nm red color