Food Lipids: Chemistry, Nutrition, and Biotechnology

Other mixed-fat systems have been studied in detail. Cocoa butter was found
to exhibit only minimal changes in polymorphism when mixed with up to 30% milk
fat [41]. Although shifts in the X-ray spectra of these blends were minimal, physical
softening of cocoa butter by milk fat and milk fat fractions has been shown [56].
Reddy et al. [61] used DSC to evaluate the polymorphic development and transitions
in cocoa butter–milk fat systems. The HMF delayed polymorph transitions, while
the LMF facilitated transformation (since the LMF is liquid at normal ambient temperatures).
Similar effects in systems of olive oil and cocoa butter have also been
observed [62]. It is probable that the liquid fat increases the mobility of the crystal
matrix, allowing more rapid conformational changes. The same mechanism may act
in LMF cocoa butter blends. The transformation inhibition by HMF supports earlier
data showing that hydrogenated milk fat inhibited chocolate fat bloom [63].
4. Effects of Emulsifiers and Other Additives
Schlichter-Aronhime and Garti [58] compared the addition of low percentages of
surfactants to cocoa butter to samples of cocoa butter blended with other fats. They
noted that fats can change the melting ranges and the number and type of polymorphs,
dependent on system compatibility, whereas surfactants may affect the rate
of transformation without sensibly altering the crystal lattice. These authors’ generalization
of work regarding surfactants and polymorphism stated that surfactants
stabilize metastable polymorphs, thereby delaying transformation to the most stable
form.
Chocolate bloom was found to be inhibited by sorbitan monostearate [64]. Also,
sorbitan tristearate was shown to inhibit the transformation of form V cocoa butter
to form VI [58]. However, in the same series of experiments, these authors found
that sorbitan tristearate hastened the transformation of the metastable polymorphs to
form V. They reported that this occurs as a result of the liquefaction effect of the
emulsifier and the liquid-mediated transformation process to form V. They reasoned
that form V is stabilized because it transforms to form VI via the solid state, simply
by expulsion of trapped liquid. Therefore, the emulsifier promotes only liquid-mediated
transformations.
The effectiveness of the emulsifier relative to its state appears conflicting.
Schlichter-Aronhime and Garti [58] stated that solid emulsifiers efficiently delay
transformations, whereas liquid ones have no effect. However, in another publication
the same authors [65] stated that ‘‘liquid emulsifiers . . . will enhance the � to �
transformation due probably to their weak structure compatibility with tristearin
which causes a higher mobility of triacylglycerol molecules.’’
Hydrogenated canola oil, which is stable in the � form, can be preserved in
the �� form by adding 3–5% of 1,2-diacylglycerol. However, 1,3-diacylglycerols
were not effective [66–68]. The action of emulsifiers on the polymorphism of fats
appears to be related to the physical structure, chemical composition, and thermal
properties of both the fat and the additive.
Like addition of emulsifiers to fats, addition to fat of seeding materials, including
triacylglycerol seeds, has also been investigated with regard to crystallization
rates and polymorphic transitions. The possibility of forming a stable � form in cocoa
butter with the addition of preformed seed crystals of cocoa butter and triacylglycerols
was investigated [69]. These data showed that a suitable seed must have a
chemical composition close to that of the predominant cocoa butter fats. This as well
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