Enhancing the consumer perception of reduced fat foods through interfacial design and rheological behaviour

We aim to develop a strategy to disguise the (low) fat content in certain food types by changing the way emulsified fats are perceived by the senses. By this route we hope to improve the consumer acceptability of healthier, reduced fat foods. Many foods contain small dispersed droplets of oil, known as emulsions to impart desirable tastes and textures. These foods, include milk, cream, yoghurts, mayonnaise, soups, sauces etc, and are estimated to form around 25% of our dietary fat intake. We aim to change the sensory perception of fat content in emulsions by controlling the outer stabilising layer of the oil droplets. We will make model foods that will be imaged in 3 dimensions whilst flowing, under conditions similar to those in the mouth, so that we can understand the fundamental processes involved. The results will be correlated with sensory perception and acceptability of these foods in human volunteers. Obesity is a major challenge facing the health of the UK population and costs the NHS an estimated £2b each year which is forecast to rise. This is blamed on a combination of diet and lifestyle. We habitually consume slightly more energy than we require, building up reserves in case of times of food shortage. This leads to a steady increase in our body mass index (BMI) with age, so that the 55-65 age range has the highest obesity rates. Small reductions in energy intake over long periods could therefore significantly reduce obesity levels. The sensory perception of fat in food emulsions is complex; thus many low fat foods are less acceptable to consumers. Improving the acceptability of these foods could help to reduce the small energy excess responsible for long term weight gain. Fat has to be emulsified into small droplets (emulsion) to keep it evenly distributed within the food. Ingredients such as proteins and other emulsifiers form a layer on the emulsion droplets to stabilise them and prevent separation. This layer affects the way the droplets interact with each other and the rest of the food, which in turn affects how we sense them in the mouth. We have shown previously that emulsions stabilised by proteins have an increased sensory perception of fat content, compared to other types of emulsifier. In more controlled experiments, we have also shown that the protein-coated droplets can increase the viscosity of the whole emulsion. We think this is because proteins form a stronger, solid layer on the emulsion droplets, whereas emulsifiers form a fluid-like layer. Our aim is to determine how the layer on the emulsion droplets enhances the sensory perception of fat content in emulsified foods. Our key objectives are:- - Develop emulsion systems that form surface layers with a wide range of strengths using proteins, emulsifiers, particles and processing methods. - Understand the complex viscosity and flow behaviour using high speed confocal (3-D) imaging under shear flow. - Design model food emulsions stabilised by these surface layers with enhanced viscosity. - Measure the sensory perception of fat content of these model foods - Determine consumer preference of new model foods compared to existing reduced fat foods. The Institute of Food Research (IFR) will develop and design a range of well controlled emulsions with defined surface properties. Leatherhead Food Research will determine the sensory and consumer response to these foods. The University of Edinburgh will use state of the art confocal imaging techniques to visualise in 3-D how the emulsion droplets are behaving under flow conditions similar to those found in the mouth. This will give more precise understanding of the mechanisms involved that will make it possible in the future to design reduced fat foods with better consumer preference. This should increase the uptake of healthier, reduced fat foods and thus help to address long term weight gain.

Our aim is to develop a rational strategy to improve the acceptability of reduced fat emulsified foods. This will be achieved by engineering the surface of emulsion droplets to increase the strength of the inter-droplet interactions. This will increase the contribution of each droplet to the overall emulsion viscosity, and hence increase the perceived fat content of the emulsion. This is based on previous work where emulsions stabilised by proteins imparted higher perceived fat contents than those stabilised by emulsifiers. Our more recent work showed that a solid, elastic droplet surface formed by proteins enhanced the interactions between emulsion droplets, whereas the fluid emulsifier surface lubricated the droplets surfaces. Work to date has focussed on concentrated emulsions, to utilise this research in foods, we need to apply the same principles to reduced fat emulsions, i.e. those for which some droplets have been replaced with a viscoelastic matrix. We will use IFR's expertise in interfacial design to develop droplets with different surface strengths, by using emulsifiers (surfactants) and proteins, but also extending this to highly elastic surfaces by crosslinking proteins and using colloidal particles. These systems will be incorporated into model food emulsions. Leatherhead Food Research will determine the sensory perception and consumer acceptability. The University of Edinburgh will study the fundamental physical interactions between the droplets within the emulsion using high speed confocal imaging under shear flow. This state of the art technique will give us a unique insight into the physics underlying how the interface influences emulsion rheology. In addition, the consumer attitudes and response to changes in mouthfeel will be examined at Leatherhead to define the barriers to consumer acceptability. Overall this methodology will improve the likelihood of successful adoption of these tailored interfaces into real foods.

Via this research we aim to determine how we can intelligently manipulate the physical and sensory behaviour of food emulsions by changing the interfacial properties of emulsion droplets. The overall goal is to improve the sensory quality of reduced fat emulsified foods. The following groups will benefit most directly from this research: Consumers would ultimately benefit from a wider choice of more acceptable, healthier food products that would aid weight control. Sustainable weight control strategies such as this ought to help reduce the long-term weight gain seen in most individuals, thus helping to contribute to the long-term health and wellbeing of the population. This may also, in conjunction with other health promoting strategies, lead to reduced health care costs involved in treating obesity and related conditions. Food industry (ingredients suppliers, manufacturers and retailers) would benefit from generic, knowledge based strategies which would facilitate the development of more acceptable reduced fat formulations. These will utilise existing ingredients and processes thus minimising production costs, and are unlikely to require additional legislative approval. Scientists & Researchers in industry and academia both experimental and theoretical who will gain new insight into the rheological characteristics of soft composite materials. Our results will add to the industrial knowledge base of the behaviour of food emulsions, enabling the development of further strategies to improve the functionality and health benefits of emulsified foods. Hence these industrialists are also beneficiaries. Emulsion science is not limited to food. Emulsions are key components in the pharmaceutical, agrochemical, paints and printing, home and personal care and petrochemical industries where emulsions are often used to solubilise, transport and deliver lipid soluble functional ingredients, often in concentrated form to reduce transport costs for downstream processing. The knowledge generated will enable scientists to develop novel, intelligent strategies to optimise emulsion rheology and behaviour for particular applications. It may even be possible to tune the effects by changing temperature or pH. Thus the outputs of this research will help scientists in these sectors to develop new approaches to control emulsion rheology and flow, thus leading to improved products and processes, reduced costs and improved consumer benefit. To facilitate knowledge transfer to beneficiaries, results will be published both in scientific periodicals and focussed trade journals to access a broad readership. Results will also be presented at conferences, particularly colloid and interface meetings which attract scientists from a diverse range of application areas. Progress will also be reported in institutional newsletters and publicity material to access a broader spectrum of stakeholders. All partners will be involved in knowledge transfer and dissemination activities where appropriate. If successful, further projects will be planned to exploit the outputs of this research. It is envisaged that further academic studies will be required to refine theoretical models describing emulsion rheology and flow. Collaborative projects with industry (both food and non-food) will be sought in order to use the research outputs to formulate emulsion based products tailored via their interfaces. IFR will encourage interaction with the food industry through dissemination via IFR's Food & Health Network to facilitate the development of further projects. The Edinburgh group will exploit its participation in the Comploids EU ITN to maximise dissemination and involvement with stakeholders.