Food Chemistry

14.5 Analysis 663

Table 14.20.Determination of the fat content of canned corned beef

Analytical method Fat content Fatty acid composition
(%)a (g/100 g)
Saturated
acids 18:1 (9) 18:2 (9,12) 18:3 (9,12,15)

1. Dried sample is extracted
   with ethyl ether 7. 93. 98 2. 06 0. 05 0. 08


2. Sample is homogenized in 95%
   ethanol and then extracted
   with ether 15. 84. 02. 60 0. 77 0. 32


3. Sample is hydrolyzed with
   4mol/1HC1(at60◦C for 30 min),
   then extracted with ether 12. 35. 66 3. 94 0. 95 0. 71


4. Sample is hydrolyzed with conc.
   HC1 (at 100◦C for 1 h), methanol
   added and then extracted
   with carbon tetrachloride 13. 92. 45 1. 68 0. 34 0. 21


5. Sample is homogenized in chlo-
   roform methanol mixture (2:1 v/v),
   washed with water and then
   the chloroform phase recovered 11. 24. 89 3. 31 0. 85 0. 39
   aThe fat is determined gravimetrically after the solvent is evaporated.

A rapid and accurate determination of fats or oils
in food is achieved by IR- (cf. 15.3.1) and^1 H-
NMR spectrometry. The method is based on the
fact that hydrogen nuclei in fluids respond to sub-
stantially higher magnetic resonance effects than
do immobilized hydrogen atoms of solid sub-
stances. Thus, the^1 H-NMR signal of a fluid, such
as an oil, differs from that of a nonoil matrix, such
as carbohydrate, protein or firmly-bound water.
The intensity of the signal is directly proportional
to the oil content. This method is also of great
value in oilseed selection or breeding research,
since it permits determination of the oil content
in a single kernel without damaging it by grind-
ing or drying, i. e. retaining its ability to germi-
nate.
The proportion of solid to fluid triacylglycerols in
fat can also be determined using^1 H-NMR spec-
trometry.

14.5.2 Identification of Fat

14.5.2.1 Characteristic Values

For both, the identification and the determina-
tion of the quality of a fat or oil, the older lipid

chemistry defines a series of characteristic val-

ues in which the reagent uptake is used to quan-

titatively estimate the selected functional groups

or calculate the constituents of a fat or oil. The

introduction of new analytical methods, such as

gas chromatography of fatty acids and the HPLC

of triacylglycerols (cf. 3.3.1.4), has made many

of these measures obsolete. The values which are

still used to differentiate fats or oils are:

Saponification Value(SV). This is the weight of

KOH (in mg) needed to hydrolyze 1 g of fat or oil

under standardized conditions. The higher the SV,

the lower the average molecular weight of the

fatty acids in the triacylglycerols (for examples,

see Table 14.21).

Acid Value(AV). This value is important for a first

quick characterization of the quality of a fat. It

is the number of milligrams of KOH needed to

neutralize the organic acids present in 1 g of fat.

Iodine Value(IV). This number is the number

of grams of halogen, calculated as iodine, which

bind to 100 g fat (cf. 3.2.3.2.1). The halogen up-

take by fat or oil is affected by the contents of

oleic (IV: 89.9), linoleic (IV: 181) and linolenic

(IV: 273) acids. Examples of iodine numbers are

provided in Table 14.21.