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Surfactants in food could speed lipid digestion

By Nathan Gray , 19-Aug-2010

The use of surfactants in food could be causing quicker break down of protein-coated lipids, according to a new study with potential to aid future food design.

The research, published in the journal Soft Matter, models protein coated lipids in foods, finding that protein coats are destabilized by interactions with surfactants leading to a quicker break down of lipids in food.

The findings offer a new focus in finding ways to control lipid digestion that may lead to the formulation of satiety inducing foods.

“Much of the fat in processed foods is eaten in the form of emulsions such as soups, yoghurt, ice cream and mayonnaise,” said Dr Peter Wilde from the Institute of Food Research.

We are unpicking the mechanisms of digestion used to break them down so we can design fats in a rational way that are digested more slowly.”

Improved understanding

The design of healthier foods to control fat uptake in the diet is an emerging area of research.

Proteins are commonly used as emulsifiers in the food industry, as they provide stabilization and can add nutritional value to products. Beta-lactoglobulin is a whey protein commonly used emulsifier in industry, due to its highly valued functional properties, but very little is understand about the influence of such food structures on the digestion of lipids.

Researchers believe that such systems are important models for testing the effects of digestive conditions on the break down of fats in food.

How emulsions behave under different digestive conditions, is an area of increasing interest as knowledge of how foods are digested could be used to create novel functional products.

Enhanced breakdown

The new study investigated the relationships between protein stabilizing layers and lipid digestion – looking specifically at the effects of the digestive enzyme pepsin on beta-lactoglobulin surface coated lipids.

The research observed that pepsin partially breaks down the normally assumed stable surface adsorbed beta-lactoglobulin molecules under gastric conditions.

The addition of surfactant, revealed a modification of the proteins, with researchers finding an “unexpected synergism” that leads to enhanced break down of the surface proteins.

Surfactants help to break down the protein layer even more effectively, improving access for the enzymes and bile salts that break down fat.

“An unexpected synergism has been revealed between surfactants and pepsin action which can lead to enhanced rupture and collapse of the protein network. These results clearly indicate that the conformation of the protein at the interface is the main determinant of hydrolysis”.

The research suggests that protein coated lipids may be more resilient to stomach conditions than previously thought, though the addition of surfactants can reduce resilience.

Next steps

The study’s observations could lead future research on the stabilization of protein coated lipids, allowing the design of food structures and manipulation of properties such as fat digestion.

"We are now experimenting with heat and enzyme treatments to reduce the synergistic effect and make the protein barrier stronger," said Dr. Wilde.

The researchers claim that if the break down of food lipids can be delayed until fats are in the ileum, their presence could stimulate satiety-inducing hormones.

“Strategies designed to strengthen the mechanical properties of the [protein coat] networks may aid transit through the stomach” wrote the researchers.

Source: Soft Matter

Published online ahead of print, doi: 10.1039/c0sm00300j

“In vitro gastric digestion of interfacial protein structures: visualisation by AFM”

Authors: J. Maldonado-Valderrama, A.P. Gunning, P.J. Wilde, V,J. Morris

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