Simulating the Adsorption of Food & Beverage Biomolecules at Fluid Interfaces
- Event time: 1:00pm
- Event date: 28th March 2011
- Speaker: Stephen Euston (School of Life Sciences & International Centre for Brewing & Distilling Heriot-Watt University Edinburgh)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
Proteins are an important functional molecule in foods and beverages. As well as providing nutritional value, proteins also contribute to the structure and texture of various foods. The functional properties for which proteins are valued include emulsification of oils and fats, foaming, gelation and thickening. The structure of the protein plays a key role in the ability of a protein to act as an emulsifying and foaming agent. In these applications the protein adsorbs to a fluid (oil-water or air-water) interface in an emulsion or foam and stabilises it against coalescence. The detailed atomic scale structure of the adsorbed protein molecules can be difficult to determine experimentally, and for this reason the technique of computer simulation, and in particular molecular dynamics (MD) are being used to complement the available experimental data. There are a number of barriers to using MD simulation for simulation of adsorption processes. The number of molecules that can be simulated is usually limited (particularly for proteins) and the timescale of simulation is short (maybe 100’s of ns but rarely much greater than a microsecond). Therefore the system size is too small to accurately investigate concentration effects and the timescale too short to probe the dynamics of unfolding. There are, however, a growing number of accelerated MD techniques (e.g. essential dynamics (ED), replica exchange MD (REMD) and coarse-grained MD (CGMD)) that promise to extend the timescale of simulations into the regions where unfolding kinetics can be probed, and fully surface denatured conformations achieved. The model protein we have chosen is barley lipid transfer protein (LTP). Barley LTP is one of the proteins responsible for the head (foam) on beer, and as such is of high technological importance to the beverage industry. The surface chemistry of beer foam is complex. LTP is the most abundant of about 30 proteins that are believed to stabilise the foam. To complicate matters further, LTP is partially denatured and reduced during the wort boiling phase prior to fermentation, and several non-native forms of LTP have been identified in beer foam. The hop iso-α-acids (bitter compounds derived from hops) are also known to improve foam stability, and it is believed that this is via interaction with the proteins in the adsorbed layer around the air bubbles. To help us understand better the role of these biomolecules in foam stability, MD, ED and CGMD simulations have been carried out to investigate the adsorption of LTP at both an air-water and decane-water interface for the isolated protein, non-native forms of the protein where some or all of the 4 disulphide bonds have been reduced, and for LTP co-adsorbing with cis-iso-cohumulone (one of the bitter compounds derived from hops).
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..