The wet jet milling process means the flour retains stable starch particles - novel properties never seen before in rice flour - and cuts out the need for food additives such as hydrocolloid gums, hydroxypropyl methylcellulose (HPMC) or glutathione.
These are often added to gluten-free flours to mimic the rheological properties of grain bread but are not necessarily seen as clean label ingredients by consumers.
“Gluten-free rice bread without any additives has been developed,” write the researchers from Hiroshima University. “Experimental evidences suggest that this is possibly a new application of the Pickering foam/emulsion in food processing.”
“The new type of bread is expected to benefit coeliac and wheat allergy patients. Further investigations will lead to the clarification of the swelling mechanism as well as to the development of new foods with unique properties.”
Pickering stabilisation describes the phenomenon that solid particles can reside at the interface of droplets and bubbles, thereby providing them with resistance against coalescence or fusion, and (debatable) coarsening or Ostwald ripening.
It is named after Spencer Umfreville Pickering who referenced it in 1907.
Source: The Royal Society of Chemistry
The soft, spongy texture of traditional wheat-based bread is thanks to gluten and its ability to form a flexible matrix. This stabilises the dough ‘walls’ that form around the CO2 bubbles released by yeast as it ferments. Gluten is also crucial in allowing the bread to rise.
These functions explain why gluten-free bread has suffered from a long-standing reputational problem of having a crumbly, rather than fluffy, consistency.
The researchers bought 11 commercially-available rice flour products from various milling companies in Japan, produced using a combination of processing methods: wet jet-milling, dry jet-milling, dry roll-milling and wet stamp-milling. They found that wet jet-milling left crucial starch particles intact.
"A piece of batter or bread was freeze-dried and subjected to scanning electron microscopy (SEM) analyses. The microstructure of the bubble wall in the fermenting batter appeared like a ‘stone-wall’ It resembled the microstructure of Pickering foam rather than that of typical wheat dough with the gluten network."
“Usage of rice flour [that has been wet jet milled] leads to successful making of gluten-free bread,” they write.
A closer look at the microstructure of the rice batter – rice flour does not form a dough that can be kneaded – revealed that the undamaged starch particles lower the surface tension of the water within the batter, thus reducing the tendency of the bubble walls to collapse.
The researchers analysed the microstructure of other rice flours that fell flat after baking and found that none contained these bubble walls, dubbed ‘stone walls’ by the Japanese food scientists.
“This tightknit ‘stone wall’ arrangement thus allows bubbles to grow and expand as CO2 levels increase within leading to successful voluminous bread.”
They also suggest the ‘stone wall’ starch bubble stability could be down to uniform hydrophobicity of the similar sized granules. They do not attract or bind to water which leaves them confined between pockets of air and the liquid batter.
They call for further analyses to focus on the thermomechanical behaviour, critical for fully understanding the mechanism behind process.
Source: Food Science and Technology
Published online ahead of print, http://dx.doi.org/10.1016/j.lwt.2016.11.086
“Development of gluten-free rice bread: Pickering stabilization as a possible batter-swelling mechanism”
Authors: Hiroyuki Yano, Akiko Fukui, Keiko Kajiwara et al.