# Gluten-Free Sourdough Based on Quinoa and Sorghum: Characterization and Applications in Breadmaking
## 1 Introduction  
The gluten-free (GF) products were initially developed for the group of consumers who suffer from gluten-related diseases or disorders. In recent years, because of a better understanding of the relationship between the GF diet and health, a growing interest of healthy consumers in GF foods has attracted the attention of food scientists. Thus, extensive research has been carried out for the development of GF food products with properties similar to conventional gluten-containing products [1]. Among the ingredients tested for replacing the wheat flour in the GF products, [PERSON] et al. [4] discussed gluten-free flours obtained from cereals, pseudocereals, legumes or seeds, as well as various types of nuts and fruit-based ingredients or refined ingredients such as starch from cassava, potato or rice, proteins, fibers and emulsifiers. The most widely investigated gluten-free cereals are rice, maize, sorghum, millet and teff. In order to balance the nutritional profile of the GF products, pseudocereals like quinoa, buckwheat, amaranth or chia can be included in various GF formulations [5; 6]. The use of pseudocereals with high nutritional and biological values in the daily diet can provide consumers with multiple health related benefits [7]. Since pseudocereals do not affect the technological functionality and quality of the complex food matrices, their use for obtaining GF products seems to be a necessity rather than a choice [6; 8]. Among the pseudocereals used to obtain gluten-free products, quinoa is of particular interest, because of its high content of minerals, vitamins, fiber, fatty acids and proteins well-balanced in amino acids, which can further help balancing the overall protein of the food matrix [9; 10]. Moreover, quinoa is a very good functional substitute for gluten, due to its rich content of soluble dietary fiber, higher than the one found in cereals, as well as due to its high content of pectic substances and xyloglucan [11]. [PERSON] et al. [12] showed that the loss of structure associated with the absence of gluten in the dough can be compensated by replacing buckwheat flour with increasing levels of quinoa flour. The dough viscosity increase with quinoa flour addition was assigned by [PERSON] et al. [12] to the higher soluble dietary fiber content of quinoa flour compared to buckwheat flour. [PERSON] et al. [13] showed that GF formulations that include up to 70% sorghum and different types of starch (corn, potatoes, rice or cassava) allow us to obtain high-quality bread products. Lactic acid bacteria (LAB) used for sourdough fermentation emerged as a useful tool for obtaining high-quality gluten-free products [14; 15]. Sourdough is a mixture consisting of flour and water, fermented with lactic acid bacteria, and eventually yeasts, and frequently used to obtain bakery products [16; 17]. While yeasts are essential for biosynthesis and release of the flavor compounds, lactic acid bacteria are primarily responsible for acidification of the sourdough [18]. There are three different sourdough production processes, differentiated based on the type of inoculum used for fermentation: type 1--traditional fermentation ensured through backslopping the spontaneously fermented flour-water mixtures; type 2--by fermentation initiated using a starter culture; type 3--using the backslopping procedure, relying on a previous fermentation process initiated by starter culture addition [19]. Even though there is no official definition, [PERSON] [20] stated that sourdough should have a pH lower than 4.5 and a LAB content higher than \(5\times 10^{5}\) CFU/g of dough. The use of sourdough in breadmaking allows us to lower the glycemic index and improve the nutritional value of the bread by increasing the bioavailability of minerals and reducing the content of antinutrients [21; 22]. Moreover, as a result of protein hydrolysis occurring during sourdough fermentation, different bioactive peptides and amino acids are released out of the native proteins [14].