## 1 Introduction  
The popularity of the gluten-free diet increased significantly in the last years, gluten-free products being popular not only among people who are intolerant or allergic to gluten but also among those who chose to have a healthy lifestyle [1]. The gluten-free diet has an important role in alleviating undesired or life-threatening symptoms in celiac or gluten-allergic patients, but careful attention should be paid to the long-term consequences caused by the nutritional limitations of the gluten-free diet. Considering the rather unique functionality of gluten in the breadmaking process and the quality of the final products, identifying a suitable gluten-free formulation for mimicking regular food products' quality, such as to meet the market demands, is challenging for food specialists. A widely used strategy for developing gluten-free products involves the use, as main ingredients, of gluten-free flours from cereals or pseudocreeals and eventually of starches, proteins and hydrocolloids [1]. [PERSON] et al. [2] pointed out that most commercially available gluten-free products are based on cheap ingredients, like rice and or corn flours, eventually combined with starch of different origins such as cassava and potato. Gluten-free products have higher amounts of fats, for improving the mouthfeel, carbohydrates and sodium, and are generally poor in high-quality proteins or fibers compared to regular products [1, 3]. Because of the high digestibility, hypoual intergenic properties, mild taste and white color [4], rice flour was used in the present study for developing gluten-free muffins. In order to balance the nutritional profile of the final product, quinoa flour was chosen to be used in ad-mixture with the rice flour. The quinoa contents of protein (14.12%), lipid (6.07%), ash (2.7%) and fiber (7.0%) are significantly higher compared to rice (6.81, 0.55, 0.19 and 2.8%, respectively) and most of the grains [5]. In particular, quinoa is acknowledged as a good source of high-quality proteins which are rich in amino acids deficient in cereals, such as lysine, methionine, histidine and threonine [6], of unsaturated fatty acids, like alpha-linoleic, oleic and linolenic acids which represent 87-88% of the total fatty acids [7] and dietary fibers [5]. Moreover, quinoa is rich in vitamins, mainly pyridoxine, folic acid and vitamin E, and minerals like calcium, iron, magnesium and potassium, in amounts considered sufficient for a balanced diet [5; 6]. In order to compensate the low protein content in gluten-free mixtures, which do not usually meet the required daily dietary amounts and affect the quality of the backed products [3], different studies focused on identifying suitable sources of proteins for fortifying the gluten-free product. Among protein sources, legumes attained the interest of researchers, and soy is of particular importance because of the good availability, low cost and multiple benefits associated with the high biological value and good functional properties [3]. Moreover, different studies highlighted the possibility of enhancing the technological functionality of these proteins by using exogenous enzymes, in addition to improving the physiological properties because of the release of the encrypted peptides with antioxidant activity, antihypertensive and anticancer properties, hypocholesterolem effects, etc. [8; 9; 10]. Unlike other physiologically active compounds, the use of peptides for providing potential health benefits to the host, through diet, is highly desired, because of the low costs, good absorption, avoidance of safety issues and contribution to nutritional value [10; 11]. The aim of the study was to investigate the impact of soy protein hydrolyses' addition on the rheological properties of the gluten-free dough and on the properties of the muffins.