From a sensory point of view, bubbles are important. From a light frothy foam in beer to a light, creamy ice cream that melts in the mouth or a fluffy dough, it is the structure of the bubbles that creates the texture.
From a food technologist’s point of view, however, they are inherently unstable: sinking, merging, popping and changing the structure of the food matrix.
A team of Swiss researchers backed by Nestlé Research Centre, have developed a method for determining bubble strength and structure that could lead to big savings on stabilisers – or being able to swap artificial stabilisers for natural ones - and longer-lasting foams.
"For the first time, we have succeeded in quantitatively controlling the dissolution arrest of foam bubbles and formulating novel, yet universally valid strategies," said lead scientist and professor for soft materials at ETH Zurich Jan Vermant. “These will help the food and materials industries to develop controlled and more effective stabilisers in order to prevent or stop Ostwald ripening."
Ostwald ripening, named after the German chemist and 1909 Nobel prize winner, is when large bubbles become larger while smaller ones shrink and then disappear – extremely difficult to stop or even slow down. Once the bubble ‘ripening’ begins, it compromises the long-term stability of the foam and surface-active components, such as protein in beer foam, only slow this process down in the short term.
"Compared to surfactant-stabilised system we gain orders of magnitude or even make the foam last essentially ‘forever'. It could be made such that it would just remain stable and not coalesce or ripen. If there is no mechanical force exerted, it would just stay there."
Stabiliser savings and cleaner labels
Post-doctoral researcher in the team, Peter Beltramo, said the findings would help industry "save a lot of materials and thus reduce costs".
However, Nestlé's interest in the project was less about cutting costs than cleaning up the labels, particularly for its ice cream portfolio, which sparked the study.
The Swiss company is currently rolling out a clean label initiative, dubbed ‘Kitchen Cupboard’, which replaces artificial ingredients with “ingredients consumers can understand and feel good about when reading the back-of-pack list”.
This means simple spices, vegetables, herbs, salt, oils, flours, starches and natural flavours, or ingredients created through basic culinary processes such as fermentation and roasting.
Senior communications manager for Nestlé R&D told us: “This [ETH foam] research looks at how natural ingredients, such as protein or fibre particles, can be used instead of traditional stabilisers. So it is not really about reducing stabilisers, but replacing them with healthier, natural ones.”
Using micrometre-sized latex particles and rice-shaped particles, they created an irregular network structure at the bubble interface. They then recreated Ostwald ripening in lab conditions, by coating individual bubbles with a controlled amount of particle stabiliser and exposing the bubbles to pressure changes.
This allowed them to determine precisely the pressure at which the bubbles begin to shrink and finally collapse.
Stabilisers create a net-like structure over the bubble which protects it. But they discovered that even partially coated bubbles can be as stable as those completely covered, which means it becomes easier to accurately predict how much stabiliser is required. A coated bubble can also withstand a much higher pressure than an uncoated one.
These ‘armored’ bubbles create foam and emulsion materials “with stable microstructures and controllable textures”, write the authors.
The ETH researchers’ findings could end up finding uses in biomedical equipment or even concrete – incorporating small, stable bubbles could make concrete lighter and more resistant to temperature changes.
Vermant’s main concern, however, was to “provide the food industry and other companies with development guidelines and quantification tools that they can use to develop new products”.
So how soon could it be before these findings are used by the wider food and drink industry?
"In principle, this could be fast, if these companies have the know-how about food grade particles," Vermant said. "I suspect a few products, which rely on the mechanism we studied, already exist without it being known."
Source: Proceedings of the National Academy of Sciences (PNAS Journal)
“Arresting dissolution by interfacial rheology design”
Available online ahead of print, doi: 10.1073/pnas.1705181114
Peter J. Beltramoa, Manish Guptab, Alexandra Alickea, Irma Liascukienec, Deniz Z. Gunesd, Charles N. Baroudc, and Jan Vermanta