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.