Secondary nucleation in triglyceride crystallization.

From published results on nucleation and crystallization of emulsified fats, on crystal size observed in the emulsion droplets, and on permeabilities as a function of the fraction of solid in the same fats in bulk, it is concluded that copious secondary nucleation can occur, explaining the high number and small size of the crystals often observed. The effect is very large for milk fat (a mixture of many triglycerides), somewhat less for a typical margarine fat, much less for a fairly simple triglyceride blend, and absent for a paraffin blend.

A hypothetical explanation is given, which implies that clusters of partially oriented molecules diffuse away from a crystal face that grows via kinetic roughening; some of these clusters may give rise to nuclei. Kinetic roughening needs a high supersaturation. A further condition would be that crystal growth is small enough for the diffusing clusters to have a reasonable life time. This hypothesis can qualitatively explain the results discussed, but would need further testing.