Multiple and composite emulsions stabilised by the interfacial protein BslA

Condensed Matter lunchtime seminar

Multiple and composite emulsions stabilised by the interfacial protein BslA

  • Event time: 1:00pm
  • Event date: 2nd November 2015
  • Speaker: (School of Physics & Astronomy, University of Edinburgh)
  • Location: Room 2511,

Event details

BslA (Bacterial Surface Layer A) is a protein expressed by Bacillus subtilis bacteria within a biofilm to provide a hydrophobic ?raincoat? at the biofilm surface. Our in vitro studies revealed that BslA is not particularly amphiphilic in solution, but can produce a hydrophobic cap ?on demand? upon adsorption to an air- or oil-water interface. After adsorption, BslA self-assembles to form a flexible, elastic film at the interface. Building on our understanding of how BslA partitions to and stabilises oil-water interfaces, we have studied emulsification using a simple BslA-triglyceride-water system by adjusting three primary parameters: oil volume fraction, BslA concentration and shear duration. Under certain conditions, we found that BslA was able to stabilise multiple emulsions (water-in-oil-in-water [W/O/W]) in a single emulsification step, a highly unusual observation that is unprecedented for a natural folded protein. In addition, shearing the emulsion for longer durations actually resulted in the creation of two phase separated emulsions, a W/O emulsion above an O/W emulsion.

We demonstrate that multiple emulsion formation is dependent on droplet-droplet collisions and that the BslA that stabilises the internal droplets can be ?recruited? from the outer O/W interface of the colliding droplets. This loss of stabiliser from the outer O/W interface can ultimately lead to the destabilisation and coalescence of the multiple emulsion drops and the subsequent formation of a separate W/O emulsion.

Finally, we have studied BslA in composite materials and discovered that rather than being removed from the interface by competing surfactants, BslA is able to function alongside them. As a result, we have created a number of BslA-stabilised multiphase composite materials, including a tasty BslA ice cream!

This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..

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