The study, published in the European Journal of Lipid Science and Technology, reports a method to prepare stable emulsions with up to 70% fish oil by adding whey protein as the emulsifying agent at a specific pH.
The research team, led by Charlotte Jacobsen from the National Food Institute at the Technical University of Denmark, reported that emulsions prepared with whey protein at pH 7.0 oxidized less or equally to neat oil, whereas, emulsions prepared at pH 4.5 oxidized more than neat oil.
“Results from the present study give an insight into the physical and oxidative stability of 70% fish oil-in-water emulsions prepared with whey protein isolate, sodium caseinate, milk phospholipids, or soy lecithin,” said Jacobsen and her colleagues.
“The emulsions can be used as delivery systems for fish oil to foods. However, only emulsions prepared with proteins at high pH offered advantages with respect to better oxidative stability during storage compared to neat fish oil … Thus, when fish oil is added to a food product in a delivery emulsion, the type of emulsion used should be carefully considered,” they added.
Fishy issue
The researchers noted that despite the steadily growing body of evidence supporting health beneficial effects of omega-3 fatty acids found in fish oils, a parallel increase in fish intake has not occurred in Western populations.
“Therefore, incorporation of marine oils into foods has gained an increased interest during the last decade … However, the highly unsaturated lipids present in fish oils are prone to lipid oxidation,” they noted.
The addition such healthy oils into food products is therefore limited by stability issues which lead to the development of unpleasant off-flavours.
“Efficient strategies for protecting the fish oil, when added to food products, are necessary in order to make fish oil enriched foods successful in the marketplace,” said Jacobsen and her team.
“A large number of studies have been performed on lipid oxidation in emulsions containing up to 40% oil and particularly on emulsions with 5–20% oil. However, oxidation studies on simple emulsions prepared with as much as 70% oil are to the author's knowledge non-existing,”
“This is despite the obvious advantage of having as high an oil content and as low a water content as possible in the emulsion, when the purpose of its use is as a delivery system, particularly in food products with a low water content,” they added.
Study details
The new study evaluated the protective effects of five different emulsifiers on lipid oxidation in 70% fish oil-in-water emulsions to be used as delivery systems for omega-3 fatty acids in foods.
The emulsifiers were either phospholipid based or protein based. The phospholipid -based emulsifiers were soy lecithin and two milk phospholipid concentrates (with either 20 or 75% phospholipid)., whilst the protein-based emulsifiers were whey protein isolate and sodium caseinate.
Lipid oxidation was then studied at two pH values (pH 4.5 and 7.0) and results were compared to lipid oxidation in neat fish oil.
Results showed that results of the study showed that an emulsion produced with whey protein at pH 7 was the most stable, lasting 46 days.
“There was a tendency toward a faster progression in lipid oxidation at low pH compared to high pH for emulsions prepared with protein-based emulsifiers,” said the researchers.
“The opposite was observed for emulsions prepared with phospholipid -based emulsifiers … Hence, at low pH phospholipid -based emulsions may be more suitable as delivery systems than protein-based emulsions,” they said.
Source: European Journal of Lipid Science and Technology
Published online ahead of print, doi: 10.1002/ejlt.201100070
“Oxidative stability of 70% fish oil-in-water emulsions: Impact of emulsifiers and pH”
Authors: A.F. Horn, N.S. Nielsen, U. Andersen, L.H. Søgaard, A. Horsewell, C. Jacobsen