Determination of Total Fat and Free Fat Content
Determination of Total Fat and Free Fat Content
Determination of Total Fat and Free Fat Content
The main problem with lipids is that they oxidise easily. This is one of
the main causes of food spoilage since, in most cases, the production
of compounds with unpleasant flavours or odours (rancidity) is
undesirable. Moreover, the oxidation of lipids can reduce the nutri-
tional quality, change the texture and colour of food and produce
compounds unsuitable for human consumption. In powders, the lipid
substrates mostly affected by oxidation are fractions exposed to air, in
the form of free fat. Three different definitions for free fat can be
found in the literature based on its properties:
1. Structural properties – associated with the presence of a damaged
protective membrane (original intact membrane of fat globules
Analytical Methods for Food and Dairy Powders, First Edition. Pierre Schuck, Anne Dolivet and
Romain Jeantet.
Ó 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd.
99
100 Analytical Methods for Food and Dairy Powders
5.1.2. Definition
The acid-butyrometric method is a conventional technique, which,
when applied to whole milk with an average fat content and an
average density, at 20 C, yields a fat content that is equivalent to that
obtained by a gravimetric reference method.
5.1.3. Principle
5.1.3.1. Dissolution of proteins by the addition of sulphuric acid.
5.1.3.2. Separation of milk fat by centrifuging the butyrometer,
with the separation being facilitated by the addition of a small
quantity of amyl alcohol.
5.1.3.3. Obtaining the fat content in grams per 100 ml of milk or in
grams per 100 g of milk by direct reading on the butyrometer scale.
5.1.6. Safety
5.1.6.1. Personal protection
Safety goggles and acid resistant gloves are essential.
5.1.7. Procedure
5.1.7.1. Preparation of a powder sample
To analyse the fat from a reconstituted liquid, rehydrate the powder to
10% (w/w) dry matter.
Determination of Total Fat and Free Fat Content 103
. churned milk
. distinct odour of fatty acid
. presence of white particles on the walls of the sample container or
fat globules on the surface of the sample.
5.1.7.3.2. Liquids
When filling the milk butyrometers, take care:
5.1.7.5. Centrifugation
Place the butyrometer in the centrifuge (i), with the neck downwards
and the cross section of the graduated stem parallel to the lid. It is
important to use an even number of butyrometers, taking care to
balance the load. Centrifuge for 6 min.
5.1.7.6. Reading
Remove the butyrometers from the centrifuge by adjusting the
stopper if necessary, to move the fat layer into the graduated stem.
Beware of acid leaks. Place the butyrometer, with the neck facing
downwards, in a water bath at 65 2 C ( j) for approximately 5 min;
the water level should be above the top of the fat layer. Remove the
butyrometer from the water bath, keeping the neck downwards at all
times, and carefully adjust the stopper in the neck, moving the layer
as little as possible, to bring the lower end of the fat layer to the
nearest gauge mark, preferably a main reference mark. Note the value
at level A corresponding to the lower end of the fat layer, and then,
taking care not to move it, and as quickly as possible (in less than
10 s), note the value at level B corresponding to the upper end of the
fat layer, which coincides with the lowest point of the meniscus. Take
the reading to the closest 0.025 g. Make at least two replicates of the
same sample for analysis.
Determination of Total Fat and Free Fat Content 105
5.1.9. Remarks
Using a butyrometer graduated in grams per 100 g of milk gives a
direct value for a product having an average density of milk. In other
cases, it is advisable to make a correction by including the specific
density of the product for analysis.
5.1.10.2. Reproducibility
The difference between two separate and independent results, ob-
tained by two analysts working in different laboratories on an
identical product subjected to the same test should not exceed
0.1 g per 100 ml.
5.1.11. Examples
This method was only carried out on powders containing fat (Table 5.1).
For these products, and given their specific composition, the fat
content ranges from 25% (w/w) (milk with 26% fat) to 52.8% (egg
yolk). Standard deviations are in the range of 1 per 1000 in absolute
terms.
Table 5.1. Fat content (wt%) of dairy and food powders
Fat (g 100 g1) Mean SD (n ¼ 3)
Milk 26% fat 25.0 1.0
Whey 40% fat 38.9 0.9
Whole egg 36.1 1.0
Egg yolk 52.8 1.1
SD, standard deviation; n, number of tests.
Determination of Total Fat and Free Fat Content 107
5.2.2. Definition
Free fat refers to the percentage of substances extracted by following
exactly the outlined method.
5.2.3. Principle
5.2.3.1. Extraction of fat by agitation of a sample in petroleum
ether. The core of the dried milk particles is not accessible in these
conditions.
b, Analytical balance.
c, 250 ml bottle with stopper.
d, Paper filter, unfolded, ash-free and fat-free, of approximately
110 mm in diameter.
e, Flask that can be used in an extraction apparatus (e.g. round-
bottom flask of a solvent extractor).
f, Oven set at 102 1 C.
g, Desiccator with an effective desiccant.
h, Solvent extractor.
108 Analytical Methods for Food and Dairy Powders
5.2.6. Safety
As regards personal protection, the wearing of safety goggles and
solvent resistant gloves is essential.
5.2.7. Procedure
5.2.7.1. Preparation of material
Put the flasks in the oven for 1 h, leave them to cool down and then
weigh them. Note the value (w).
5.2.7.3.9. Lay the bottle on its side for leave for 1 h in the oven ( f ).
5.2.9. Remarks
5.2.9.1. Given that the analysis and comprehension of the data
concerning free fat in milk powders was so complex, Vignolles et al.
(2007) recently published a literature review on the different
analytical and physicochemical factors that could influence the
free fat content and consequently the quality of fat-enriched milk
powders.
5.2.10.2. Reproducibility
The difference between two separate and independent results, ob-
tained by two analysts working in different laboratories on an
identical product subjected to the same test should not exceed
0.1 g per 100 g.
5.2.12. Examples
This method was only carried out on powders containing fat
(cf. Table 5.1and Table 5.2). For these products, the free fat content
ranges from 2.1% (grams per 100 g of fat) (milk with 26% fat) to 7.6%
(egg yolk).
Table 5.2. Free fat content (wt%) of dairy and food powders
Free fat g 100 g1 of fat g 100 g1 of powder
(n ¼ 3) Mean SD Mean SD
Milk 26% fat 2.1 0.1 0.5 0.0
Whey 40% fat 5.1 0.2 2.0 0.1
Whole egg 7.4 0.2 2.7 0.1
Egg yolk 7.6 0.1 4.0 0.1
SD, standard deviation; n, number of tests.
Determination of Total Fat and Free Fat Content 111
5.3. Bibliography
AFNOR 1990. Norme NF V 04-210. Lait – D etermination de la Teneur en
Matiere Grasse – M ethode Acido-Butyrom etrique. Association Française de
Normalisation, Paris.
FIL-IDF, Norme internationale 152A 1997. Lait et Produits Laitiers – D etermi-
nation de la Teneur en Mati ere Grasse – Guide de Directives G enerales
Appliquees aux M ethodes Butyrom etriques. Federation Internationale de
Laiterie, Brussels.
Vignolles, M.L., Jeantet, R., Lopez, C. and Schuck, P. 2007. Free fat, surface fat and
dairy powder: interactions between process and product. A review. Le Lait, 87:
187–236.
Vignolles, M.L., Lopez, C., Madec, M.N., Ehrhardt, J.J., Mejean, S., Schuck, P. and
Jeantet, R. 2009a. Protein-lactose matrix affects fat encapsulation during the
overall spray-drying process of dairy powders. Australian Dairy Journal, 64:
75–79.
Vignolles, M.L., Lopez, C., Ehrhardt, J.J., Lambert, J., Mejean, S., Jeantet, R. and
Schuck, P. 2009b. Methods’ combination is a key tool to elucidate the
suprastructure, composition and properties of fat in fat-filled dairy powders.
Journal of Food Engineering, 94: 154–162.
Vignolles, M.L., Lopez, C., Le Floch, C., Ehrhardt, J.J., Mejean, S., Jeantet, R. and
Schuck, P. 2010. Fat supramolecular structure in fat-filled dairy powders: a tool
to adjust drying kinetics. Dairy Science and Technology, 90: 287–300.