Identifying key interactions to reduce astringency of novel food proteins

作为生物科学促进可持续农业主题的一部分，开发供人类消费的新的植物性或合成蛋白质来源是BBSRC的一个主要目标。今天，对高蛋白食物的需求已经通过增加畜牧业来实现，但这对环境的影响现在正在实现。因此，最近的一个发展是合成蛋白质的配方，以及在结构化食品的生产中越来越多地使用植物来源的蛋白质。提高消费者对这些新食品的喜爱程度对他们接受和发展这一新兴行业至关重要，而英国在这一行业中处于领先地位。然而，新型食品蛋白的开发已经达到了瓶颈，因为许多这类蛋白质在食用时会导致过度的口腔涩味。涩味是一种口感干燥、起皱的感觉，通常与茶和葡萄酒中的单宁有关。低水平的涩味可以给消费者带来一种清新的感觉，但高水平的涩味对摄入有抑制作用。单宁酸引起涩味的机制还不太清楚。儿茶素（茶和酒中的主要多酚类物质）中的酚环通过疏水-疏水相互作用堆积在唾液蛋白（如脯氨酸蛋白和粘蛋白）中的脯氨酸环上。这种结合可能通过消耗唾液蛋白周围的水合层和失去润滑而导致口腔润滑减少。这种润滑的丧失被认为是干燥，即使液体仍然丰富。对于蛋白质引起的涩味，我们只有从牛奶中提取的乳清蛋白的有限数据，乳清蛋白通常用于增肌/营养饮料。乳清蛋白通过与唾液蛋白形成静电相互作用而收敛，尽管证据仅与体外实验有关，尚未完全了解。静电的相互作用很可能是引起涩味的重要原因，因为许多化学物质也会引起同样的感觉。例如，明矾是一种水合硫酸铝盐，众所周知，它通过影响唾液蛋白质的构象来影响它们的润滑，从而导致涩味。到目前为止，还没有已知的涩味感受器，而感知到的干燥被认为是通过改变触觉和口腔中的本体感受器激活来检测的。如果我们能够了解食物蛋白质和唾液蛋白质之间相互作用的本质，就有可能筛选潜在的新食物蛋白质的涩味，并开发出修改蛋白质的方法来减少这些相互作用。这对Motif公司来说尤为重要，因为他们将从银杏中筛选大量潜在的蛋白质，用于开发食物蛋白质。因此，本项目的总体目标是确定由食物蛋白质引起的口腔涩味的机制。为了达到这一目的，我们将测试静电相互作用是食物蛋白质和唾液蛋白质之间主要界面的假设。为了实现这一目标，该项目的目标是：1)改变食物蛋白质和唾液蛋白质之间的静电相互作用2)识别产生电荷相互作用的蛋白质基序3)检查反离子在破坏涩味中的作用为了进行这个项目，学生将结合生理学和蛋白质生物化学，并使用结构生物学来详细检查相互作用的性质。

The development of new plant-based or synthetic sources of protein for human consumptionis a major aim of the BBSRC as part of the Bioscience for sustainable agriculture theme. Todate the need for high protein foods has been achieved by increased animal farming but theenvironmental impact of this is now being realised. As a consequence a recent developmenthas been the formulating of synthetic proteins and the increased use of plant derived proteinsin the creation of structured foods. Improving the consumer liking of these new foods isessential to their acceptance and growth of this new industry, in which the UK is a leadingplayer. However, the development of novel food proteins has reached a bottleneck as manyof these types of protein cause excessive oral astringency when consumed. Astringency isthe dry, puckering sensation in the mouth often associated with tannins in tea and wine. Atlow levels astringency can be a refreshing sensation which is enjoyed by the consumer but athigher levels it is inhibitory to ingestion. The mechanism of how tannins cause astringency isreasonably well understood. Phenol rings within the catechins (which are the mainpolyphenols in tea and wine) stack onto proline-rings within salivary proteins such as Prolinerichproteins and mucins by hydrophobic-hydrophobic interactions. This binding then causesa reduction in oral lubrication possibly by depleting the hydration layer around the salivaryproteins and a loss of lubrication. This loss of lubrication is perceived as dryness, eventhough liquid is still in abundance. For protein induced astringency we only have limited datafor whey protein, derived from milk, which is commonly used for muscle-building/ nutritiondrinks. Whey proteins are astringent by forming electrostatic interactions with salivaryproteins although the evidence relates only to in vitro experiments and not completelyunderstood. It is likely that electrostatic interactions are important in causing astringency asa number of chemicals can also cause the same sensation. Alum, for example, is a hydratedaluminium sulphate salt which is widely known to cause astringency and does so by affectingthe conformation of salivary proteins to affect their lubrication. As yet there are no knownreceptors for astringency and the perceived dryness is assumed to be detected by alteredtouch and proprio-receptor activation in the mouth. If we can understand the nature of theinteractions between food proteins and salivary proteins it may be possible to screen potentialnew food proteins for astringency and develop methods to modify the protein to reduce theseinteractions. This is of particular importance to Motif as they will be screening large numbersof 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 byfood proteins. To achieve this aim we will test the hypothesis that electrostatic interactionsare the main interface between food proteins and salivary proteins. To achieve this theobjectives for the project are:1) To vary electrostatic interactions between food proteins and salivary proteins2) Identify protein motifs that create charge interactions3) Examine the role of counter ions in disrupting astringencyTo conduct this project the student will combine physiology with protein biochemistry and usestructural biology to examine the nature of the interactions in detail.