# Gluten-Free Sourdough Based on Quinoa and Sorghum: Characterization and Applications in Breadmaking
## 3 Results
### Sourdough Properties
SC1 consists of a mixture of two facultative heteroferlectrative lactic acid bacteria, namely _Lacticaseibacillus thannosus_ and _Lactiplantobacillus plantarum_, and the obligately heteroferlectrative strain of _Levilactobacillus brevis_, which are able to both hexoses and pentoses. In addition to lactic acid, ethanol and acetic acid are produced from acetyl-P via the phosphoketolase pathway in the heterofermentative metabolism of hexoses and pentoses, respectively [34]. Glycerol might be as well used as a substrate for producing acetic acid. SC2 includes a mixture of two homoformetative, microaerophilic lactic acid bacteria, namely _Lactobacillus acidophilus_ and _Streptococcus thermophilus_ and the heterofermentative _Bifidobacterium lactis_ strain. In the case of the SC2 fermented sourdough samples, the homolactic metabolisms of both hexoses and pentoses resulted in highest amounts of lactic acid (\(p<0.05\)), regardless of the GF flour blends. Lactic acid is the main product of homolactic metabolisms under both anaerobic and aerobic conditions [34]. Additionally, the respiration conditions may cause a shift in the metabolisms of homoformetrative lactic acid bacteria towards additional major metabolites, such as acetate and acetoin [34]. No aeration was ensured during sourdough fermentation to support the lactic acid bacteria respiration over the entire incubation period. Therefore, in the case of _Lactobacillus acidophilus_ and _Streptococcus thermophilus_, the lactic acid was the main end product of the homofermetative metabolism, of both hexoses and pentoses, via the Emden-Meyerhoff and pentose phosphate pathway, respectively. The presence of ethanol and acetic acid in the SC2-fermented sourdough samples is the result of the heterofermentative metabolism of carbohydrates via the phosphoketolase pathway by _Bifidobacterium lactis_ and the presence of native microbial flora in the GF flours. The TPC and antioxidant activity of the sourdough samples are summarized in Table 4. Regardless of the starter culture used for preparing the sourdough, the TPC decreased with the increase in the sorghum flour addition (\(p<0.05\)). These results were expected considering that the TPC of quinoa and sorghum flours used in the experiment were 2.04 \(\pm\) 0.02 and 1.08 \(\pm\) 0.01 mg fertile acid/g d.w., respectively. A similar decreasing trend was observed for the DPPH-RSA, which is mainly due to the phenolic compounds found in the samples [41]. On the other hand, the ABTS-RSA significantly increased (\(p<0.05\)) with sorghum level (Table 4), suggesting the larger participation of the compounds originating from sorghum flour to the reduction mechanisms of the ABTS\({}^{+}\) by the electron transfer of an antioxidant. Both lipophilic and hydrophilic antioxidants are quantified through ABTS-RSA [41]. In the case of all tested GF flours, the use of the starter culture for initiating the sourdough fermentation favored the release of the TPC, resulting in significant improvement of the DPPH-RSA values (\(p<0.05\)) compared to the corresponding spontaneously fermented samples (Table 4). The intense lactic fermentation might facilitate the extraction of different bioactive compounds from the GF flour. Moreover, the bioactive compounds biosynthesized by lactic acid bacteria during sourdough fermentation might contribute to the radicals scavenging protentional of the samples [26]. The highest values of DPPH-RSA were obtained in the case of the sourdough samples fermented with SC 1.  
known that proteins have an important role in the water absorption of the flour. Sorghum has a lower protein content (9.50 g/100 g d.w.) compared to quinoa (15.83 g/100 g d.w.) (Table 1). The sorghum proteins mainly consist of karfirrine, cross-linked karfirine, albumins, globulins and glutelins [43], of which the karfirine fractions are highly hydrophobic [44]. On the other hand, quinoa contains chemopodine made of subunits of 49 and 57 kDa linked by disulfide bonds, with the 49 kDa subunit being the principal component [45].