Relating crystallization behavior of monoacylglycerols-diacylglycerol mixtures to the strength of their crystalline network in oil.

Diacylglycerols (DAGs) are interesting oil structuring molecules as they are structurally similar to triacylglycerols (TAGs), but are metabolized differently which results in weight loss and improved blood cholesterol levels upon dietary replacement of TAGs with DAGs. Many commercial products consist of a mixture of monoacylglycerols (MAGs) and DAGs, yet the effect of MAGs on the crystallization behavior of DAGs is still to be unraveled. Two types of commercial MAGs, one originating from hydrogenated palm stearin and one of hydrogenated rapeseed oil, were added in concentrations 1, 2 and 4% to 20% DAGs derived from hydrogenated soybean oil. Using differential scanning calorimetry, it was shown that the presence of MAGs delayed the onset of DAG crystallization. Rheological analysis revealed that MAGs also hindered crystal network development. Synchrotron X-ray diffraction analysis demonstrated that the addition of MAGs suppressed the formation of the ß form and stimulated the development of the ß' form. Likely, MAGs mainly hindered the crystallization of 1,3-DAGs, which are responsible for the development of the ß form, and stimulated the crystallization of the 1,2-DAGs, which can crystallize in the α and ß' forms. The presence of two polymorphic forms resulted in a decrease of the crystal network strength, as was derived from oscillatory rheological measurements. This research implies a different effect of monoacylglycerols on both the nucleation and crystal growth of 1,2- and 1,3-DAG isomers. This insight is not only relevant for oleogelation research, but also for emulsifying agents which often contain blends of MAGs, 1,2-DAGs and 1,3-DAGs.

Influence of cooling rate on partial coalescence in natural dairy cream.

The presence of a fat crystal network throughout the fat droplets of an oil-in-water emulsion is a requisite for partial coalescence. The characteristics of this fat crystal network determine greatly the kinetics of partial coalescence. In this study the fat crystal network was manipulated by altering the cooling rate applied to natural cream. The kinetics of partial coalescence under constant shear and at constant temperature were studied by combining rotational viscosity analysis with light microscopy and laser scattering. It was shown that slow cooling of the emulsion decelerates partial coalescence and favors the formation of loosely-packed aggregates. On the other hand, fast cooling favors a high partial coalescence rate and the formation of dense aggregates. Fat crystallization properties were analyzed using small deformation rheology, differential scanning calorimetry and cryo-scanning electron microscopy. The difference in organization of the fat crystals obtained for both cooling rates contributed significantly to the mechanistic understanding of partial coalescence as influenced by the cooling rate.

Crystallization behavior of emulsified fats influences shear-induced partial coalescence.

Emulsion stability is desired during production, storage and transportation. However, controlled destabilization by partial coalescence is requisite in the production of e.g. whipped cream, vegetable toppings and ice cream. Partial coalescence in recombined cream (RC) implies the presence of a semisolid fat. Three types of fat, i.e. anhydrous milk fat (AMF), palm oil (PO) and palm kernel oil (PKO), were used in the production of RC. Partial coalescence was initiated by the application of shear and assessed at three temperatures, namely 15, 20 and 25 °C to investigate the relation between solid fat content (SFC) and shear-induced partial coalescence. Despite differences in SFC, shear-induced partial coalescence occurred fastest at 20 °C. On the contrary, a nearly equal SFC at 25 °C resulted in significantly different behavior amongst the fats. This demonstrates that not only SFC determines instability but also fat crystal microstructure, which is dependent on fat composition and on processing conditions. However, SFC could be related to the type of network formed by the partially coalesced fat droplets. The fat crystallization properties, studied in bulk and emulsion, point out a divergent effect of emulsification on the crystallization of the fats which could be explained by differences in crystal morphology.