The study, published in the Journal of Agricultural and Food Chemistry, finds that one particular type of gliadin, known as gamma- gliadin, is mainly responsible for its foaming properties. The study also suggested that foam stability was best at neutral and alkaline pH values.
Researchers into foam-based food products, such as whipped cream, ice cream, sorbets, and mousses, continues, with food companies such as Unilever leading the way: Stability is an issue with food foams.
The new research found that, at neutral and alkaline pH values, foams were quite stable, with more than 60 per cent of the foams still being present after 60 min.
“We showed that the foaming properties of gliadin strongly depend upon the pH … Moreover gamma-gliadin contributes most to the foaming properties of gliadin, irrespective of the pH,” said the authors, led by Bert Thewissen from the Katholieke Universiteit Leuven, Belgium.
“Our experiments confirm their suggestion that these forces should be considered in the context of the stability of air bubbles … In this respect, the present results contribute to an understanding of the gliadin foaming behaviour and the underlying mechanisms,” they added.
Gliadin is a glycoprotein that is found in wheat and several other cereals. With glutenin, gliadin is known for its role in the formation of gluten, and is essential to giving bread the ability to rise properly and fix shape during cooking thanks to it enabling the formation of viscoelastic dough.
Whilst dough elastic and strength properties are attributed to glutenin, gliadins are said to act as ‘plasticizers’ that act to weaken interactions between glutenin chains, thereby increasing dough viscosity.
Previous research studying the properties of gluten, gliadin, and glutenin foams showed that gliadin plays a predominant role in gluten-foaming properties.
The authors said that gliadins are classified into omega-, beta-, and gamma-gliadins. It has been previously suggested that gamma- gliadin foams are of higher stability than omega- gliadin foams, while beta- gliadin foams are less stable.
Thewissen and colleagues explained that the degree at which foams can be created from liquids is proportional to the surface tension of these liquids; the lower the surface tension, the easier it is to create foams, they said.
“Although the adsorption of gliadins at surfaces in model systems has been described quite well, data on the relationship between the surface-active properties of gliadins on one hand and the foaming properties of gliadins on the other hand are scarce,” they said.
They added that because of this, it is not clear which gliadin type contributes to the foaming properties.
“The aim of our work was to elaborate on the foaming properties of gliadin. These were determined as a function of pH and linked to gliadin solubility, surface tensions, and the distribution of the different gliadin types. Furthermore, the effect of NaCl on the foaming properties of gliadin was examined,” said the researchers.
Thewissen and co workers reported that gliadin has excellent foaming properties only at neutral and alkaline pH.
In addition to the stable foams at neutral and alkaline pH values,the researchers found that foams at acidic and alkaline pH values are enriched in gamma-gliadin, while foams at pH 8.0 have a similar distribution of beta- and gamma-gliadins – therefore concluding that gamma-gliadin predominantly contributes to the foaming properties.
The poor foaming properties of gliadin at low pH values were improved in the presence of 0.25 and 1.0 per cent sodium chloride (NaCl).
“Our results indicate that chloride ions mask positive charges on the protein chain at acidic pH, leading to decreased surface tensions and improved foaming properties,” said the authors.
They said that this observation was in line with previous research showing that the addition of salt at pH levels above or below the isoelectric point (the pH at which a molecule carries no net electrical charge) results in increased protein adsorption because of charge masking.
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, doi: 10.1021/jf103473d
“Foaming Properties of Wheat Gliadin”
Authors: B.G. Thewissen, I. Celus, K. Brijs, J.A. Delcour