In modern processed foods, fat (lipids) from plants and animals is put into food in the form of emulsions. Examples include spreads, imitation creams, salad dressings, gravies, sauces, soups, confectionery and chocolate. Lipids play a major part in determining the texture, flavour and taste profile of these foods, and they provide essential fatty acids that the human body cannot produce itself. They also act as carriers of pre-formed fat-soluble vitamins (vitamins A, D, E and K).
Food researchers are beginning to realise that the behaviour of emulsions in the gastrointestinal tract is affected by their physico-chemical properties and that they modulate fat digestion and consequently influence the bioavailability of lipid nutrients. This area of research needs to be further developed before the knowledge can be used to develop specific strategies for controlling fatty acid absorption and bioavailability.
The emulsion science research undertaken by Riddet Institute researchers Professor Harjinder Singh and Dr Aiqian Ye is at the forefront of this new field. They want to know how the action of the enzyme lipase is modified by the composition and the structure of adsorbed layers on the emulsion droplet surface, the role of bile salts in exchanging/displacing original emulsifying material from the emulsion droplet, the final state of the droplet when it is ready to be absorbed and how the emulsion droplets interact with enterocyte membranes for transport into the blood system. Finding this out will help to design functional foods that could manipulate the bioavailability of fatty acids, which will aid people with high blood lipid levels and at a high risk of cardiovascular disease and obesity.
Creating food emulsions requires generating stable oil-water interfaces, which are critical in determining the interactions of droplets with other components in foods. Phospholipids and proteins can be used as emulsifiers, but monoacylglycerols and diacylglycerols also often feature as emulsifiers and stabilisers. Until recently, the research emphasis has been on understanding how the composition of interfaces of emulsion droplets can be manipulated to control the stability of emulsions in order to improve product quality.