Fat crystallization with talc particles is influenced by particle size, concentration, and cooling rate

We recently found that new types of additives including talc promoted the crystallization of monoacid saturated triacylglycerols (TAGs) in stable polymorphs. This study reports the effects of size and concentration of talc particles and cooling rate on the crystallization of trilauroylglycerol (LLL), tripalmitoylglycerol (PPP), and 1,3-dipalmitoyl-2-oleoyl glycerol (POP). Talc particles were mixed with molten TAGs, and the mixtures were then cooled at designated cooling rates. Polymorphic crystallization was observed by simultaneous use of X-ray diffractometry and differential scanning calorimetry and by polarized optical microscopy. The following results were obtained: (i) talc promoted the crystallization of LLL in stable polymorphs with decreasing particle size and increasing concentration; (ii) the promotional effects were influenced by the cooling rate; (iii) the same behavior was observed for PPP and POP; and (iv) hydrophobic modification of talc surfaces did not affect the promotional effects. These results indicate that talc particles having median sizes of less than 2.5 μm and concentrations exceeding 0.1 wt.% effectively promote fat crystallization, and that the promotional effects can be maximized by choosing proper cooling rates according to the target fats. Furthermore, we propose a model of the heterogeneous nucleation of TAG crystals taking account of the molecular adsorption on cleavage surfaces of talc. 1 Practical applications Talc is widely approved as a food-grade ingredient, and the additive effects on various triacylglycerols widen its applicability to fat-based food and cosmetic materials. With grinding, talc particles exhibit anisotropic surfaces: cleavage surfaces are hydrophobic, and edge (lateral) surfaces are hydrophilic. Hydrophobic modification of the edge surfaces does not affect the additive effects of talc particles on fat crystallization, indicating adsorption of fat molecules on the cleavage surfaces.