How is fat content determined by soxhlet method?

Answer 1

The Soxhlet method for determining crude

fat content is a lengthy process requiring up

to a day for a single analysis. The solvent

extraction step alone takes six hours. The

method is therefore not favoured for routine

testing purposes in the meat industry, rather

it is used as a standard reference method.

As well as being used to determine the fat

content of meat and meat products, the

Soxhlet method can be used to determine

the fat content of meat meal. In the case of

meat meal, the Soxhlet method is often the

method of choice as a routine test.

Crude fat content is determined by

extracting the fat from the sample using a

solvent, then determining the weight of the

fat recovered. The sample is contained in a

porous thimble that allows the solvent to

completely cover the sample. The thimble is

contained in an extraction apparatus that

enables the solvent to be recycled over and

over again. This extends the contact time

between the solvent and the sample and

allows it time to dissolve all of the fat

contained in the sample. In order for the

solvent to thoroughly penetrate the sample it

is necessary for the sample to be as finely

comminuted as possible.

Before the solvent extraction step can begin

the sample must be dried. Often a moisture

analysis is required as well as a fat analysis

and this can be achieved by accurately

weighting the sample after drying and before

extraction, as well as before drying. If a

moisture analysis is not required the sample

need only be weighed before drying and

again after solvent extraction. In either case

the sample must be weighed accurately on

an analytical balance at each stage of the

analysis.

When the sample is being weighed it is

important not loose any part of it including

any moisture that may weep from the sample

during weighting. Loss of this moisture can

be avoided by weighing the sample directly

into a pre-dried extraction thimble or

alternatively on to a pre-dried filter paper. If

a moisture analysis is required, the dried

extraction thimble or filter paper also has to

be pre-weighed. After weighing, the sample

(in the thimble or filter paper) can be placed

in the oven for drying. After drying, the

sample can be placed directly into the

distillation apparatus for extraction.