Secondary nucleation in triglyceride crystallization

Abstract

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.

Isothermal crystallization behaviour of milk fat in bulk and emulsified state

“…Although only small or no differences in crystallization temperature between milk fat in cream and in bulk were observed, the explanation can mainly be found on the level of nucleation. When primary nucleation, whether homogeneous or heterogeneous, occurs in a bulk milk fat, the crystallization can readily spread throughout the whole liquid via secondary nucleation at severe supercooling (Walstra, 1998). Secondary nucleation will also occur if milk fat is dispersed in numerous globules but only in the globule in which primary nucleation took place.…”

“…Interdroplet nucleation can occur when solid globules are mixed with supercooled liquid droplets through a collision mediated mechanism (Dickinson, Kruizenga, Povey, & Vandermolen, 1993;McClements & Dungan, 1997;McClements, Han, & Dungan, 1994), but this rarely occurs in practice. Secondary nucleation can take place in bulk and emulsified fats which contain a wide range of TAGs and is initiated when small clusters of TAG-molecules diffuse away from the crystal surface (Walstra, 1998). Furthermore, it need be mentioned that the nucleation type and rate, both in bulk systems and emulsions, will also be affected by the entire t,T-program and flow conditions.…”

Palm Oil and Palm Kernel Oil: Versatile Ingredients for Food Applications

“…Fat crystallisation, types of oils and fats used in the formulation and controlling process operation in the fat food industry are crucial in order to produce margarine products of desired quality (Sellami et al, 2012;Himawan et al, 2006;Metin and Hartel, 1998;Walstra, 1998). Hydrogenated liquid vegetable oils had been widely used as hard stock for good margarine shortening consistency since the introduction of hydrogenation technology in the early nineteenth century (O'Brien, 2008).…”

Effect of sugar, cocoa particles and lecithin on cocoa butter crystallisation in seeded and non-seeded chocolate model systems

“…The crystallisation process was divided into two parts, nucleation and crystal growth, both of which have an impact on the kinetics of cocoa butter crystallisation (Garside, 1987;Walstra, 1998). In order to investigate the effect of each ingredient, different chocolate model systems were developed by adding one ingredient at a time to cocoa butter followed by precrystallisation.…”