This thesis aims to enhance understanding of the sensory properties of protein fortified foods during oral processing by studying flow and lubrication behaviours. During oral processing, saliva plays an important role through mixing with samples, dilution and varying degree of interaction with proteins. However, the role of saliva in sensory perception of protein-based foods is not yet fully understood. A systematic review screening 36,604 articles narrowing down to 33 articles highlighted that although oral processing and salivary interactions of dairy proteins particularly at low protein concentrations are relatively well understood, little is known about plant proteins, particularly at higher concentrations. As a result, this thesis aimed to gain a deeper understanding of the role of different protein types, both in the presence and absence of model saliva, during oral processing. To accomplish this, the research methodology chosen used a diverse range of techniques combining instrumental analysis looking at lubrication properties with human sensory evaluations. Two plant proteins, pea protein concentrate and soy protein isolate, were compared to two dairy proteins, whey protein isolate and sodium caseinate with the addition of a control, skimmed milk powder. Systems were analysed in a range of protein concentrations (5wt%-20wt%) and in different media of varying complexity, from aqueous solutions to oil-in-water emulsions to finally a model food. In general, plant proteins demonstrated poor adsorption, solubility and lubrication properties. This was shown to impair their sensorial mouthfeel (measured using Quantitative Descriptive Analysis (QDA®) when implemented in a model food system. Increasing protein concentration improved lubrication for dairy but not for plant proteins. Although the friction was decreased when proteins were in an emulsion system owing to oil-induced lubrication, still the high friction coefficients of plant proteins were apparent. Overall, the addition of model saliva to proteins had little effect on lubrication, with protein still dominating the frictional dissipation with disparate degree of influence on adsorption behaviour in plant versus dairy proteins. In summary, simpler systems with plant protein in bulk solutions can provide mechanistic insights about lubrication and adsorption behaviour, which are often challenging to pinpoint when they are present in model food systems. Overall, food manufacturers may require careful formulation engineering strategies to mitigate lubrication-mediated sensory differences when transitioning towards plant proteins to achieve sustainable formulation in the future.
