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Nr. 98, 30.03.2019  voriger  Übersicht  weiter

Nanostructures from whey protein

Dr Julia Keppler uses all the tools of food technology in order to get whey protein to produce emulsions or ultra-thin films. She is presenting her project at the Hannover Messe.

Food technologist Dr Julia Keppler characterises amyloid protein structures and their properties. Credit: pur.pur

Whey is the watery, green-yellow liquid that is left over when milk is processed into cheese. Dried whey, or whey powder, mainly contains lactose (milk sugar) and high quality protein. In agriculture it is used as feed, and in food production as an additive. The raw material is also interesting for food technology. "Whey contains high-quality protein and is readily available," emphasised Dr Julia Keppler from the Institute of Human Nutrition and Food Science at Kiel University. The scientist is especially interested in the -lactoglobulin contained in whey, abbreviated as BLG. "This is one of the best characterised proteins of all. We know the structure and know exactly how it behaves."

She uses the protein in order to produce so-called amyloid aggregates. Due to their structure and surface activity, these have properties that can be used for food processing. In order to produce the desired amyloid aggregates from BLG, it is dissolved in acid pH and then kept for five hours in a water bath at 90 degrees Celsius. The procedure destroys the protein's original structure. Small peptides are created which join together to form new structures - long thread-like strands, small balls or worm-like structures.

By heating for several hours at acid pH, the whey protein -lactoglobulin proteolyses into shorter peptides. These arrange themselves in the shape of folded strands (fibrils). The amyloid aggregates formed in this way have special properties and could be used for coating food, for example. Credit: Dr. Julia Keppler

However, these structures cannot observed with the naked eye or under a light optical microscope. Outwardly, only the somewhat viscous, gel-like solution suggests that amyloid structures are present. The dried final product is a fine white powder, just like the starting product. "We are working in the nanometre range, and cannot see what has changed with the naked eye - so we need special techniques," explained the scientist.

She uses a whole range of methods to analyse the form and function of the products. "For example, we highlight using a fluorescent dye which specifically binds to certain structural patterns, the so-called -sheets, or measure the conformation of proteins at different points in time during the process using infrared spectroscopy. In the first year of the project, we initially optimised methods with which we can represent what we produce."

Protein strands seen under an atomic force micro­scope. Credit: Dr. Julia Keppler

Keppler is currently working with liquid interfaces, and stabilising foams and emulsions. The next goal is to produce solid films which can be used for coating surfaces, for example to protect food against oxidation. Until then, the properties of the structures produced from whey protein must first be analysed precisely. Among other things, they are investigating which functional properties are associated with the different morphologies. Some questions include: How stable are the aggregates during processing? Can they be used to stabilise emulsions? How strongly do the products oxidise? Keppler: "We have also examined where we can intervene during the manufacturing process to speed up the formation of peptides or fine strands by pre-treating the protein with ethanol or enzymes."

The food technologist is convinced that this effort is worthwhile, because transparent films or coatings based on edible, food-grade and biodegradable materials are rare.

Kerstin Nees
The work is part of a priority programme of the German Research Foundation (DFG) (SPP 1934 - DiSPBiotech). The Kiel sub-project is led by Dr Julia Keppler, together with Professor Karin Schwarz and Dr Anja Steffen-Heins.
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