The solid content of viscoelastic emulsion drops is known to affect their propensity for aggregation and their subsequent coalescence behavior, where the balance between the drive to reduce surface tension and the straining of an internal viscoelastic network is able to create a plethora of stable partially coalesced states.
While partial coalescence in food emulsions has been widely studied, the mechanism of stabilization of different partially coalesced states has not been fully illuminated. This mechanism is important for a fundamental understanding of emulsions as well as practically in many aspects of food technology. In dairy foods, partial coalescence can often be observed due to the part solid nature of milk lipids. The presence of such partially coalesced emulsion drops can enhance destabilization, particularly on temperature cycling, where full coalescence manifests as a consequence of the melting of fat crystals whose viscoelastic properties had previously helped to stabilize the partially coalesced state.
We carry out experiments aided by optical tweezers using micron-sized emulsion drops generated from milk fat. For several decades now, optical tweezers have proved their usefulness in many studies at the micro and nanoscale. In the present study, we examined the partial coalescence of partially crystalline fat droplets in simulated milk ultrafiltrate (SMUF) solution as a function of temperature. The degree of arrested coalescence was controlled by manipulating the concentration of crystalline fat in the drops using either local heating of the droplets with a high-powered laser; or by heating the microfluidic chip in which the experiments were being conducted.
About the speaker
Dr. Mariela Rodriguez Otazo recently finished her postdoctoral fellowship at Massey University in New Zealand where she investigated the aggregation of partially crystalline droplets manipulated by holographic optical tweezers. As an experimental physicist, she started her career focusing on Applied Optics, developing a great interest in the optical tweezers’ technique. She received a Ph.D. in Physics in 2008 carried out at the Aimé Cotton Laboratory, Paris XI University in France, where she studied the rotation of microcrystals under polarized light in an optical trap. After, Mariela joined the Nanoscience Institute S3 at Modena and Reggio Emilia University in Italy as a postdoctoral fellow to study the NCS-1 protein folding mechanism using a counter-propagating optical trap.