The researchers used proteins called hydrophobin HFBII at a concentration of only 0.1 per cent to produce a foam with exceptional stability, that could lead to improvements in the physical and sensory properties of a range of products, including low fat whipping cream, ice cream and sorbets, states the authors in the journal Food Hydrocolloids.
"In the presence of a thickening agent to slow the rate of creaming, hydrophobin can stabilise foam to the extent where little, or no, air phase loss is observed, for over 4 months," wrote lead author Andrew Cox from Unilever R&D, Colworth Science Park. "In fact, we have an example where most of the air phase volume remains after 2.5 years storage at chill temperature."
"The stability of such foams are well in excess of those stabilised using other common food aerating/emulsifying agents, such as milk proteins and Tween," added Cox.
The key to the foams is hydrophobins, a class of fungal proteins, which, in their isolated form, could have significant potential for food formulations. Concerns over safety or a history of consumption were eased by the researchers, since many are presently consumed with hydrophobins being present in mushrooms.
Food foam formulation
"The ability to produce a stable liquid foam, without needing to rely on a gelled or solidified continuous phase, has long been a desire of food manufacturers, but has never been realisable in practice," explained the researchers.
A solution to this problem could lead to significant opportunities for food manufacturers, they added, and products could be improved in terms of functionality, new textures, or a reduction of the calorific density per volume through aeration.
Cox, Deborah Aldred, and Andrew Russell compared the stability of aerated solutions produced using the hydrophobins with that of typical and commercial aerating agents and food emulsifiers: sodium caseinate (DMV International), ß-lactoglobulin (Sigma), Hygel 8293 (hydrolysed milk protein, Kerry Biosciences), Tween (Sigma).
The hydrophobin, described as a Class II Hydrophobin (HFBII) from Trichoderma reesei was obtained from VTT Biotechnology, and foams were prepared with and without xanthan (CP Kelco), which was employed as a stabiliser/ thickening agent.
"In simple solutions, we have found that 0.1 weight per cent HFBII forms exceptionally stable foams across a wide range of solution pH conditions," stated the researchers.
Proof in the chocolate pudding
To show the potential for food formulations, Cox, Aldred, and Russell prepared a chocolate milk shake.
Despite the presence of other ingredients, like cocoa powder, fat, protein, and sugar, the HFBII-containing foam phase exhibited "good stability" when stored at five degrees Celsius for five weeks.
"HFBII can reduce the air/water surface tension to values below that of the other surface active agents present," they stated. "Once adsorbed at the bubble surface, the addition of other ingredients do not appear to greatly inhibit the surface stabilising capacity of the hydrophobin protein in such a food product."
"Use of hydrophobins could further lead to the possibility of aerating food products that currently do not contain air because of instability problems: for example, mayonnaise, shelf-stable milk shakes, smoothies and other beverages, yoghurt, and gelatine-free mousse," stated Cox in Food Hydrocolloids.
"As a result, benefits such as fat/calorie reduction or improved/new product textures are possible," they added.
Both the corresponding author and Unilever PLC were contacted for comment regarding future plans for the food foams, but no-one was available for comment in time for publication.
Source: Food Hydrocolloids
Published online ahead of print 7 March 2008, doi:10.1016/j.foodhyd.2008.03.001
"Exceptional stability of food foams using class II hydrophobin HFBII"
Authors: A.R. Cox, D.L. Aldred and A.B. Russell