Selection of lipid extractors and sample pre-treatment.

the presence of fat in food has free state, but also binding state. Free-form fats such as animal fats and plant-based fats. The binding state of fat, such as naturally occurring phospholipids, glycolipids, lipoproteins, etc., is formed by the formation of
proteins
or carbon water
compounds
and other components. For most foods, free-state fat is the main, binding state of fat content is less.
, the choice of extractors
fat structure is more complex, until now no solvent can extract pure fat, that is to say, extracted are coarse fat. (Mostly fat, and some other ingredients).
the properties mentioned earlier, lipids are insoluble in water and soluble in
organic
solvents. Most of the lipids were determined using organic solvents with low boiling points. Commonly used solvents are ether, petroleum ether, chloroform-methanol mixture solvents. Among them, ether dissolves fat with strong ability and is most widely used. Below we talk about their characteristics:
(i) ether (non-polarity) advantages and disadvantages
1, advantages
(1) ether boiling point is as low as 34.6 degrees C
(2) solvent fat capacity is stronger than petroleum ether
2, disadvantages
(1) can be saturated by 2% water
(1) 2) Water-containing ether pumping capacity is reduced (oxygen and water can form hydrogen bonds to penetrate
tissues
capacity is reduced, i.e. pumping capacity is reduced)
(3) water-containing ethanol is non-fat component dissolved, and is pumped, so that the results are high (sugar protein, etc.)
(4) make the result high, and ether flammable.
we have a set of experiments below, through which we can compare the results
extraction of lecithin 25 cmg / 100g
low molecular component waterless ether
glucose 10.5mg/100g315mg/100g
cane sugar 15mg/100g 150mg/100g
serine 015mg/100g
NaCl025mg/100g
thus it can be seen that ethanol contains water, can dissolve the non-fat components of the sample to increase the weight of the results, therefore, when using ether, the sample can not contain water, must be
dry
. And when using ether, the room needs air flow. Because ether is in the air, the maximum allowable concentration is 400 ppm, which exceeds this limit and is prone to explosion.
In addition, ether is generally stored in brown bottles placed for a period of time, light exposure will produce peroxide, peroxide is also prone to explosion, if ether storage time is too long, before use must check for peroxide, if there should be removed.
3, the method of checking peroxides
ether in a small amount of Fe2 plus a small amount of KCNS to appear red, indicating that there have been oxides present, and the reverse is colorless, the method of excluding peroxides is as follows.
4, the method of excluding peroxide
containing peroxide ether and FeSO4 (small amount) ------ can remove peroxide
.