Food Lipids: Chemistry, Nutrition, and Biotechnology

ected interesterification of palm oil led to a broader melting profile with no distinct
peaks. Rossell [70] studied the effects of chemical interesterification on palm kernel
oil crystallization. Randomization did not alter the shape of the crystallization curve;
only peak temperatures were slightly lower. Because of the wide range of triacylglycerols
that must be packed into fat crystals, interesterified fats generally show
simpler melting curves with less polymorphism upon chemical interesterification
[68].
Zeitoun et al. [71], who examined interesterified blends of hydrogenated soybean
oil and various vegetable oils (1:1 w/w ratio), found that each oil influenced
the melting and crystallization behavior of the interesterified blends differently as a
result of initial variations in oil composition. Rousseau et al. [34] found that chemical
interesterification of butterfat–canola oil blends also led to simpler, more continuous
melting profiles. However, overall changes were minimal.
5. Cone Penetrometry
This is a rapid yet empirical method used in the evaluation of fat texture and rheology
[72]. Jakubowski [43] found that interesterification doubled penetration depth of a
blend of 35–65% tallow–sunflower oil blends, at 15�C. Rousseau et al. [73] reported
that interesterification substantially decreased the hardness index of blends of butterfat
and canola oil. Other rheological measurements include viscoelasticity measurements
[73].
6. X-Ray Diffraction
The polymorphic behavior of fats is important in many food systems (fat spreads,
chocolate, etc.) [52]. Fat spread crystals exist as one of three primary forms: �, ��,
and �. The � modification is to be avoided in fat spreads because it results in a
sandy texture [72]. The �� crystals are the most desirable form. Chemical interesterification
alters the crystal morphology and structure of fats. Larsson [74] stated
that a greater variety of fatty acids hinders �-crystal formation. Hence, upon interesterification
of butterfat, which normally consists of a predominance of �� crystals
and a slight proportion of �-crystals, the latter disappeared upon triacylglycerol randomization
[68,75,76].
List et al. [77], while working with margarine oils, found that chemical interesterification
and blending of vegetable oils and hydrogenated hardstock of soybean
oil or cottonseed oil resulted in ��-crystal polymorphs.
Hernqvist et al. [52] interesterified mixtures of tristearin, triolein, and trielaidin.
These mixtures were chosen to produce model systems for vegetable oil blends used
in margarine. Polymorphic transitions of interesterified blends were studied, and depending
on the blend, two to four polymorphs (sub-�, �, ��, or�) were observed.
7. Polarized Light Microscopy
The morphology of the crystals comprising the three-dimensional fat crystal network
is largely responsible for the appearance and texture of a fat and exerts a profound
influence on its functional properties. Interesterification leads to noticeable modifications
in crystal morphology, which can be examined in great detail with polarized
light microscopy [78]. Prior to interesterification, lard consists of large crystals promoting
graininess. Following interesterification, tiny delicate crystals, typical of the
�� polymorph, are present [79]. Becker [80] performed an in-depth study on the
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