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Breakthrough technique could unravel emulsions

By Stephen Daniells , 06-Jul-2010

Our understanding of the stability of emulsions may leap forward as UK scientists report the use of an atomic technique to probe the interactions of pectin.

Researchers from the Institute of Food Research led by Prof Vic Morris used a technique called atomic force microscopy (AFM) to probe the emulsifying properties of sugar beet pectin – an ingredient receiving increasing attention because it has unusual emulsifying properties.

The AFM technique has already been applied to studying interactions between oil and water droplets in emulsions, said the researchers, but this is the first time AFM has been applied to sugar beet pectin in order to study interactions between emulsion droplets, said the researchers.

The findings, published in the journal Soft Matter, may facilitate the design of emulsions with improved quality, said the IFR, and to engineer such structures to produce new functional foods with improved nutritional and health benefits.

The focus on pectin

Pectin, with worldwide production estimated at 35,000 tonnes a year, is currently widely used as gelling agents in jams, confectionery, and bakery fillings, and stabilisers in yoghurts and milk drinks.

The majority of pectin used currently comes from citrus peel and apple pomace. The functionality of pectin is dictated by the chemical fine structure, and other sources of the ingredient, like sugar beet and pumpkin, have remained largely unexploited because of certain undesirable structural properties.

Emulsions are blends of two or more liquids that don’t normally mix, like oil and water. In order to stabilise the dispersion of an oil, for example, in a liquid like water food scientists turn to emulsifiers. These ingredients work electrostatically to stabilise oil suspended in water – part of the emulsifier is attracted to water, while another part is attracted to the oil.

In order to understand the emulsifying properties of sugar beet pectin, Prof Morris and his team applied the AFM technique. The technique works by measuring surface interactions to provide quantitative data on surface forces. This data is then interpreted using computer models and an ‘image’ of the surface forces is produced.

Applying the technique to sugar beet pectin allowed the scientists to obtain images of the interfacial films of pectin with oil and water. At a pectin level of 0.1 per cent – the lowest concentration used – the researchers observed large holes in the pectin layer.

“The existence of such defects (holes) supports the idea that the sugar beet pectin forms an elastic network at the interface which prevents lateral diffusion and thus prevents perfect packing,” explained the researchers. “The holes disappear at the higher concentration (0.5 per cent) and the layer of chains becomes denser,” they added.

“As some of our results suggest the direct study of droplet interactions can reveal new and unexpected effects specific to the case of deformable surfaces and which could be important in understanding droplet interactions in real emulsions, as well as other soft matter systems,” wrote Prof Morris and his team.

“In order to extract more quantitative data from such experiments, theoretical models which account for the droplet deformation under different types of interactions will need to be developed in the future.

“This will provide a deeper understanding of the stabilising effects of interfacial structures and molecular mechanism underpinning the functional properties of emulsions,” they concluded.

The research was supported by the Biotechnology and Biological Sciences Research Council (BBSRC).

Source: Soft Matter
Published online ahead of print, doi: 10.1039/c0sm00089b
“Molecular basis of the emulsifying properties of sugar beet pectin studied by atomic force microscopy and force spectroscopy”
Authors: A. Gromer, R. Penfold, A.P. Gunning, A.R. Kirby, V.J. Morris

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