Identifying key interactions to reduce astringency of novel food proteins

The development of new plant-based or synthetic sources of protein for human consumption
is a major aim of the BBSRC as part of the Bioscience for sustainable agriculture theme. To
date the need for high protein foods has been achieved by increased animal farming but the
environmental impact of this is now being realised. As a consequence a recent development
has been the formulating of synthetic proteins and the increased use of plant derived proteins
in the creation of structured foods. Improving the consumer liking of these new foods is
essential to their acceptance and growth of this new industry, in which the UK is a leading
player. However, the development of novel food proteins has reached a bottleneck as many
of these types of protein cause excessive oral astringency when consumed. Astringency is
the dry, puckering sensation in the mouth often associated with tannins in tea and wine. At
low levels astringency can be a refreshing sensation which is enjoyed by the consumer but at
higher levels it is inhibitory to ingestion. The mechanism of how tannins cause astringency is
reasonably well understood. Phenol rings within the catechins (which are the main
polyphenols in tea and wine) stack onto proline-rings within salivary proteins such as Prolinerich
proteins and mucins by hydrophobic-hydrophobic interactions. This binding then causes
a reduction in oral lubrication possibly by depleting the hydration layer around the salivary
proteins and a loss of lubrication. This loss of lubrication is perceived as dryness, even
though liquid is still in abundance. For protein induced astringency we only have limited data
for whey protein, derived from milk, which is commonly used for muscle-building/ nutrition
drinks. Whey proteins are astringent by forming electrostatic interactions with salivary
proteins although the evidence relates only to in vitro experiments and not completely
understood. It is likely that electrostatic interactions are important in causing astringency as
a number of chemicals can also cause the same sensation. Alum, for example, is a hydrated
aluminium sulphate salt which is widely known to cause astringency and does so by affecting
the conformation of salivary proteins to affect their lubrication. As yet there are no known
receptors for astringency and the perceived dryness is assumed to be detected by altered
touch and proprio-receptor activation in the mouth. If we can understand the nature of the
interactions between food proteins and salivary proteins it may be possible to screen potential
new food proteins for astringency and develop methods to modify the protein to reduce these
interactions. This is of particular importance to Motif as they will be screening large numbers
of potential proteins from their partner Gingko for development as food proteins.
Thus the overall aim of this project is to identify the mechanism of oral astringency caused by
food proteins. To achieve this aim we will test the hypothesis that electrostatic interactions
are the main interface between food proteins and salivary proteins. To achieve this the
objectives for the project are:
1) To vary electrostatic interactions between food proteins and salivary proteins
2) Identify protein motifs that create charge interactions
3) Examine the role of counter ions in disrupting astringency
To conduct this project the student will combine physiology with protein biochemistry and use
structural biology to examine the nature of the interactions in detail.