Food Chemistry

666 14 Edible Fats and Oils

The detection of adulteration of oils and fats has
been improved further by coupled HPLC and GC
of the minor constituents. The saponification of
the sample is not required, free and esterified
compounds being detected separately.
An example is the differentiation between the
olive oil qualities “extra vierge”and“lampante”.
After esterification of the free OH-groups with
pivalic acid, the free fat alcohols, wax esters,
free acids, triterpene alcohols and esters are
eluted in a relatively narrow fraction in HPLC
and separated from the triacylglycerides. The
eluate is transferred to a gas chromatograph

Fig. 14.7.On-line HPLC-GC of sterol and wax frac-
tions of olive oils.a“Extra vierge” oil,b“lam-
pante” oil. Peak 1: sitosterol, peak 2: 24-methylene cy-
cloartenol, peak group 3: wax esters, peak 4: sitosterol
ester, peak 5: 24-methylene cycloartenolester (accord-
ing toGrobet al., 1991)

and analyzed on an apolar capillary column. As

shown in Fig. 14.7, a clear distinction is made

between “lampante” oils and “extra vierge”

oils because the former have high contents of

wax and sterol esters (sitosterol, 24-methylene

cycloartenol) (cf. 14.3.2.1.1).

14.5.2.5 Melting Points

In addition to specific density, index of refraction,

color and viscosity, the melting properties can be

used to identify fats and oils.

The composition and the crystalline forms

(cf. 3.3.1.2) of triacylglycerols present in fat

determine the melting points and the temperature

range over which melting occurs. The onset, flow

point and end point of melting are of interest.

They are determined by standardized procedures.

The melting properties of fat are more accurately

determined by differential thermal analysis. The

temperature difference is measured between the

fat sample and a blank, i. e. a thermally inert

substance, as a function of the heating tempera-

ture (Fig. 14.8). In this way the temperatures at

which polymorphic transitions of fat occur are de-

tectable. In addition, the content of solid triacyl-

glycerols can be assessed from the heat absorbed

during melting at various temperatures. Thus, the

solid triacylglycerol (TG) portion of coconut oil

at− 3 ◦C can be calculated using data from the

recorded curve (Fig. 14.8) and the following for-

mula:

% Coconut(solid TG)=

Area(BCDE)

Area(AEDA)

· 100

(14.11)

The solid: liquid ratio of acylglycerols is of im-

portance in fat hydrogenation and interesterifica-

tion processes (cf. 14.4.3). This ratio can also be

assessed using the Solid Fat Index by measuring

the expansion of the fat, i. e. the volume increase

of a fat during its transition from solid to liquid

and by^1 H-NMR spectroscopy (cf. 14.5.1).

14.5.2.6 Chemometry

To solve difficult problems in food chemistry,

e. g., the detection of the authenticity of olive