*3.3. Breads Characterization*

Sorghum and millet breads are characterized by lower specific volumes and higher crumb firmness compared to quinoa and rice flour breads (Table 3). Marston et al. [40] reported an improvement of the specific volume and crumb firmness of gluten-free breads based on heat-treated sorghum flour compared to the unheated flour. The authors noted that these results are possible due the modification of sorghum proteins by oxidizing the free sulfhydryl groups. Moreover, Taylor et al. [2] suggested that the lack of glyco- and phospholipids in sorghum flour might be a reason for the lower volume of the bread prepared with sorghum flour compared to the wheat. In addition to starch, the properties of the lipids influence to high extent the crumb firmness.


**Table 3.** Physical properties of quinoa, sorghum, millet and rice breads.

The quinoa bread had the highest specific volume and lowest crumb firmness. Elgeti et al. [1] reported enhanced specific volume of the bread made with quinoa flour compared to the bread made with a blend of rice and corn flours. The authors explained these results through the better ability of the dough prepared with quinoa flour to retain a high amount of gas. It is well known that the proteins from rice flour do not have great gas retention properties [41]. The high gas volume resulting throughout fermentation was stabilized within the network during baking, resulting in a nice structure with homogeneously distributed fine pores. It was considered that different surface-active components present in quinoa flour, such as peptides or polar lipids, might contributed to the stabilization of the gas bubbles. In addition, the viscoelastic properties of the dough might be optimized such as to allow easier and more efficient gas inclusion and stabilization. Furthermore, Elgeti et al. [1] noted that specific volume of bread increased when quinoa flour was used to replace the quinoa whole flour. They considered that the positive effect registered on the volume of the bread was the result of

removing the embryo hull components out of the whole flour. As previously shown, the bran particles might interfere with gas cells, affecting the porosity and specific volume bread [42].
