Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 15 Solid content index of cocoa butter and randomized cocoa butter measured by
dilatometry: �, native cocoa butter; ●, randomized cocoa butter. (Adapted from Ref. 28.)
D. Milk Fat
Much research has been done on the chemical interesterification of milk fat. Milk
fat, like most fats, does not have a random distribution, which conveys a predetermined
set of physical properties. Butyric and caproic acids, for example, are predominantly
located at sn-3, while palmitic acid is mostly at sn-1 and sn-2 [88]. Other
fatty acids are not as specific. Interesterification of milk fat can be a powerful means
of modifying its functional properties.
Weihe and Greenbank [89] presented the first paper dealing with the chemical
interesterification of milk fat, with details appearing in Weihe [90]. These investigators
performed randomization of milk fat at 40–45�C for 20 minutes to 6 hours
with 0.1–0.3% Na/K alloy. For directed interesterification, xylene or hexane was
added before the reaction, which was begun at 25–38�C and dropped in three to five
steps to 10–25�C. Directed interesterification led to more substantial changes than
random interesterification (e.g., on solid fat; Fig. 16). Increases in melting point were
greater in the presence of a solvent than without, and direct interesterification generated
larger increases in melting point than random interesterification.
Interesterification increased the softening point of milk fat by 3.7–4.2�C, which
was explained by higher proportion (5–7%) of high-melting triacylglycerols, which
translated into a higher hardness. Mickle [91], on the other hand, found that interesterification
reduced the hardness of butter and also led to a rancid, metallic flavor.
Refining (free fatty acid removal and steam injection under vacuum) removed the
undesirable flavor, yet the final product was tasteless. Finally, an in-depth study by
Mickle et al. [92] revealed the effects of three interesterification reaction parameters
on the hardness of a semisolid resembling butter. All three parameters—duration
(5–55 min), temperature (40–90�C), and catalyst concentration (0.5–5%) had sta-
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