The ageing of gel-like materials composed of tiny water-born oil droplets that weakly adhere to one another is the focus of new research at the UK-based Institute of Food Research.
According to the IFR, these aggregated emulsions, which are models of commercially important foods such as salad dressings and smoothies, can actually collapse over time in a way that nobody really understands.
Scientists at the institute in Norwich explain in a recent paper the crux of the research. "Using new techniques based on tracking large numbers of individual droplets, we can see exactly how these materials evolve over time, and use this information to put together a theory that will ultimately help create new compositions and products."
Their particular focus is on dispersions of particles or droplets in a fluid background, where some degree of attraction causes the dispersed phase to aggregate together and form a gel.
" The concentration of the dispersed phase and the strength of the aggregating interaction control how strong the gel is, and this in turn dictates whether the material is more a 'soft-solid' or a 'complex fluid'," they write.
In food materials, these properties are apparent to the consumer as 'mouthfeel', or the way the sauce 'gloops out of the bottle', though they may not affect the food safety or nutritional quality, they are nevertheless deemed undesirable, say the researchers.
This last property, the physical stability and aging of dispersions, in particular in emulsions, is an on-going interest at the IFR. An emulsion is a dispersion of droplets of one liquid, typically oil, in a background of another liquid, usually water.
"Butter is an emulsion consisting of water droplets in oil, whereas cream is an emulsion of oil droplets in water: same stuff, but different material properties and also different microbial ageing properties (cream goes sour more quickly than butter because bugs can move about better in a water background)," add the scientists.
According to the IFR scientists, by working with emulsions, 'we are looking at the way weak gels, in other words aggregated dispersions, collapse in time due to the influence of gravity'.
For food manufacturers concerned about the separation of emulsions over time, notably on the supermarket shelf, this investigation will certainly hold some interest.