Lead author Anita Fechner and co-workers from the Department of Food Technology at the Friedrich-Schiller-University Jena report that using proteinpolysaccharide conjugates could lead to the production of emulsions with improved stability to changes in pH and temperature.
"These results are an important basis for the discovery of new emulsifiers for preparing dispersed food systems with customised properties and for preparing double emulsions with different release behaviours," wrote Fechner.
"This could broaden the possibilities for using protein-stabilised emulsions in food containing acid or salt."
The research taps into growing interest in the development of water-in-oil-in-water (W/O/W) emulsions. These 'double' emulsions involve water-based droplets dispersed inside oil droplets further dispersed inside an aqueous phase. Current application of the technique is limited due to difficulties with the stability of the internal water droplets, a problem that could be solved by using the protein-polysaccharide conjugates.
The research looked at the potential of stabilising water-in-oil-in-water (W/O/W) emulsions with conjugates of sodium caseinate (SC) and dextran (Dex). Vitamin B12 was used as a model encapsulate in the study, and the release of the vitamin from the inner to the outer aqueous phase measured.
Writing in the journal Food Hydrocolloids, Fechner and her co-workers report that the double emulsions with encapsulated B12 were prepared using a two-step process.
The inner aqueous phase consisted of water, sodium chloride, gelatin (5 per cent, to promote gelling of the aqueous phase) and 1 per cent vitamin B12, and this was homogenised (distributed evenly) to form the emulsion with the oil phase - polyglycerol polyricinoleate (PGPR, Imwitor 600) and MCT-oil (caprylic/capric triglyceride, Miglyol 812), provided by Sasol Germany GmbH.
The double emulsion was subsequently prepared by homogenising this water-in-oil emulsion with a second aqueous phase containing the SCDex conjugate or pure SC.
Fechner reports that the water-containing oil droplets of the W/O/W emulsions prepared using the SC-Dex conjugate were smaller with uniform size distribution.
"The use of SCDex500 conjugates instead of the pure protein depressed the vitamin B12 release significantly after acidification and heating as well as during storage of emulsions with 2 per cent PGPR," they said.
"A reason for the higher encapsulation efficiency could be a more stable interfacial film caused by using the SCDex500 instead of the pure protein."
When the pH of the emulsion was reduced to create an acidified environment, it was found that the release of vitamin B12 into the outer water phase decreased significantly, from 40 to 30 per cent when using the SC-Dex conjugate emulsifier.
"The advancement of the encapsulation efficiency of vitamin B12 in the double emulsions by using only 2 per cent PGPR as hydrophobic emulsifier offers the opportunity to increase the inclusion of bioactive components even at low emulsifier concentrations in the oil phase," they said.
The researchers state they are continuing to look at ways to optimise the conjugate formation, and other effects on double emulsions.
"In order to improve long-term stability of double emulsions made by natural substances and to diminish or substitute substances which have to be declared (e.g. PGPR), the combination of such proteinpolysaccharide conjugates as hydrophilic emulsifiers with natural W/O emulsifiers such as fractionated lecithins could be a possibility."
Source: Food Hydrocolloids
Published on-line ahead of print, doi:10.1016/j.foodhyd.2006.10.021
"Stability and release properties of double-emulsions stabilised by caseinatedextran conjugates"
Authors: A. Fechner, A. Knoth, I. Scherze and G. Muschiolik