Seeds of two native species of Plantago have been identified as producing mucilage that can be used as a natural additive to make gluten-free bread dough more elastic, resulting in fluffier loaves.
The seeds of P. turrifera (left) and P. ovata (right), with mucilage gel released on the seed. Credit: University of Adelaide.
The research was conducted by a team led by the University of Adelaide's Dr James Cowley, who discovered the differences in mucilage content and chemistry of each Plantago species affected its suitability for use as a food ingredient.
"The differences in mucilage led to wildly different impacts when added to gluten-free breads," says Dr Cowley.
"Adding Plantago flour made the doughs more elastic, making them more resistant to collapsing during fermentation, which made breads with better appearance and texture.
"We believe this comes down to the differing chemistries of the mucilage, as the amount alone did not explain the effects. For example, two native species, P. cunninghamii and P. turrifera, produced similar or better-quality breads to commercial P. ovata, despite having much lower mucilage content."
Mucilage is a sticky gel of pure dietary fibre that is produced by many seeds when they are wetted. An example of this is chia seed pudding, which has a gooey texture thanks to the mucilage they produce.
Dr Cowley has studied Plantago seeds for more than a decade and says desire is increasing among coeliacs and non-coeliac gluten-avoiders for better gluten-free bread products that don't have such long ingredients lists.
"Consumers are increasingly looking for 'clean label' products that are perceived as 'healthier' or 'more natural'," says Dr Cowley.
"Hydroxypropylmethylcellulose, known as HPMC or E464, is one of the most common gluten replacements in bread but is often met negatively, as it is perceived as 'artificial' or 'unnatural'.
"Psyllium husk, which is extracted from Plantago ovata for use in gluten-free doughs, can be included on ingredient labels as vegetable fibre without the need for an E number, allowing it to be more 'clean label'."
Dr Cowley says the research, published in Food Hydrocolloids, also shows that whole-seed flours - those which use the inner seed parts as well as the mucilage-containing husk - are preferable to those in which the mucilage is removed.
"Commercial psyllium husk is made by removing the mucilage through a grinding process, but this produces a large amount of waste with no high-value commercial use, despite our group recently showing that the waste is high in nutrients," says Dr Cowley.
"We hope that more products may use Plantago whole-seed flour, which still contains that beneficial mucilage, as a more sustainable alternative to purified psyllium husk."
Hydrated psyllium husk showing its viscous stretchy behaviour that lets it replicate some functions of gluten. Credit: University of Adelaide.
Most importantly, the resulting breads were softer, springier and had more volume.
"Consumers consider texture and appearance to be critical to their perception of a quality gluten-free bread, and they are looking for springy, airy loaves that behave as closely to gluten-containing breads as possible," Dr Cowley says.
"We aren't quite there yet, but new additives and formulations appear all the time. Hopefully one day we can produce clean-label gluten-free breads that are just as good as the real thing."
Dr Cowley and colleagues are narrowing the quality gap between gluten-free and traditional breads through follow-up research.
"We are now beginning to understand why mucilage chemistry plays a big role in improving the quality of gluten-free breads made with Plantago flour," he says.
"My brilliant PhD student, Lucija Štrkalj, a co-author on this paper, recently successfully defended her PhD thesis and made some exciting discoveries about how the mucilage chemistry leads to more elastic networks in food products."
