Scientists from the South China University of Technology report that the technique could extend the application of gels to allow for the incorporation of heat sensitive food ingredients.
Writing in the journal Food Chemistry, the authors said that until now, techniques have relied on heat-setting techniques to produce gelled emulsions, but noted that heat treatment of the emulsion limited the uses of the gels, due to the heat sensitivity of certain bioactive food ingredients.
“Protein-stabilized emulsions are systems of great importance to the food industry … This kind of novel gel-like emulsion might exhibit great potential and be applicable in food formulations …[as a] carrier for heat-labile and active ingredients,” said the authors, led by Dr Fu Liu from the Department of Food Science and Technology at the South China University of Technology.
Whey proteins are an important nutritional and functional food ingredient, and are extensively used in food applications, including sport beverages, meat replacement products, baked products, salad dressings, ice creams, artificial coffee creams, soups and dairy products.
Liu and colleagues said that compared with emulsions, emulsion gels have more potential when applied as the carriers for bioactive compounds in functional foods, due to their controlled release profiles and improved oxidative stability.
They noted that whey protein-stabilized emulsions can be transformed into emulsion gels, through heat treatment, and acidification with glucono-delta-lactone (GDL) however Dr Liu and co workers noted that the heat setting process may not be suitable for many forms of bioactive compounds.
“Heat-set emulsion gels are clearly not suitable as the carrier for heat-labile bioactives … those obtained by cold-set techniques without heat treatment will be much more favourable,” they said.
They added that a recently developed novel cold setting technique has been recently reported to produce gel-like emulsions from whey protein concentrate at ambient temperatures.(Food Hydrocolloids, doi: 10.1016/j.foodhyd.2009.02.011).
“[Previous research] indicated that the gel-like emulsion showed a high thermal stability and could be used as an alternative to concentrated oil/water emulsions and in food formulations containing heat-sensitive ingredients,” said the authors.
The new study investigated the rheological and micro structural characteristics of the novel cold-set gelled emulsions.
Liu and colleagues said the cold-set gel emulsion was produced from whey protein concentrate, by thermal pre-treatment of the whey protein at 70 °C for 30 minutes, followed by the microfluidization techniques.
Upon assessment, the formation of the gelled emulsions was found to be closely related to the high emulsifying efficiency of whey proteins – however the rheological and micro structural properties were found to be highly dependent upon the oil fraction of the emulsion.
However Liu and co workers reported a close relationship between the rheological properties and gel network microstructures of the gelled emulsions. They noted that laser scanning microscopy analyses confirmed this close relationship.
Rheological analyses indicated that the cold-set gel emulsions showed shear-thinning and predominantly elastic gel behaviours.
The apparent viscosities and the mechanical properties of the emulsions were found to “remarkably and progressively” increase with increasing the phi value of the emulsion – from 0.2 to 0.6.
The authors concluded that the cold-set gelled emulsions were stable, and may have great potential for the use in food formulations, as the cold-set nature of the gel would allow bioactive compounds to be incorporated into formulations without suffering damage from a heat-setting process.
Source: Food Chemistry
Published online ahead of print, doi: 10.1016/j.foodchem.2011.02.031
“Cold, Gel-like Whey Protein Emulsions by Microfluidization Emulsification: Rheological Properties and Microstructures”
Authors: F. Liu, C.H. Tang