Role of salivary films in assessing the quality of foods

Replacement of fat, sugar and salt, and the incorporation of benefit agents into foods typically renders the product unacceptable to consumers due to mouth-feel and taste considerations. This project focuses on the physiology of assessing food quality through the interactions with saliva which exists as a film within the mouth. How food interacts with this salivary film is basic research that is poorly understood and yet is central to our understanding of how we perceive food. To investigate the role of saliva on taste and mouthfeel perception we will examine the composition of salivary films taken from different parts of the mouth at rest and following interaction with foodstuffs known to have other qualities apart from the five basic tastes. Tea, although bitter, causes astringency by interacting with salivary proteins incorporated in the salivary film and thus generates the dry, puckering sensation felt around the mouth. The CASE student will combine the expertise and capabilities developed at both the academic and industry research groups. Recent work by Carpenter et al., reveals the salivary film interface to be highly surface elasticity, generated primarily due to a calcium-rich layer and adsorption of the protein statherin at the air interface (Proctor et al., 2005). The project will also utilise techniques and expertise developed within Unilever Corporate Research on the measurement of bulk rheology (viscoelasticity), lubrication, and adsorbed film architecture of stimulated and unstimulated saliva (Bongaerts et al., 2007;Stokes & Davies, 2007). The composition of the salivary films will be mimicked in vitro to make a detailed analysis of their physical properties in order to relate composition of salivary films with sensory perception. This will allow some of the basic mechanisms that allow us to perceive food qualities beyond the five basic tastes to be investigated. It is envisaged that such a study will enable the intelligent design of in-vitro models for adsorbed salivary films using appropriate protein combinations, which could subsequently be used to determine how food and beverage components interact with oral and other internal biosurfaces, as well as influence sensory perception. This may also allow food, beverage, and oral care products to be designed with control over their interaction with targeted proteins or specific components; this is desirable for controlling the delivery of benefit agents as well as for improving the sensorial reward of products with healthier compositions. The objectives are; 1. Sample and analyse by SDS-PAGE salivary films from different mucosal surfaces compared to WMS. Determine how tea polyphenols (or other foodstuff such as mayonnaise (fat/ cream) and weak citrus acid (in soft drinks) interact with proteins present in WMS and mucosal salivary films by electrophoresing protein/ polyphenol mixtures (Carpenter et al., 2005). 2. Characterize the interfacial and bulk rheological properties of saliva in relation to its composition. Bulk rheology of whole mouth saliva (WMS) arises from large molecular weight mucin glycoproteins secreted from the sublingual/submandibular glands. In contrast, interfacial rheology of saliva is dominated by adsorption of statherin to the air-liquid interface surface (Proctor et al., 2005). This objective will examine the bulk and interfacial rheology of parotid and submandibular/sublingual saliva alone and mixed in different proportions. Results from these experiments will indicate the mechanism by which the rheological properties of saliva are altered during stimulation by foodstuffs. 3. Examine effect of foodstuffs rheological properties of specific components of salivas Interfacial and bulk rheology of e.g. Muc 5B and synthetic statherin.