## 2 Materials and Methods
### Muffin Characterization  
The muffin samples were characterized by assessing the main physico-chemical characteristics within 24 h after samples cooling to room temperature.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Ingredients**} & \multicolumn{6}{c}{**Muffin Samples**} \\ \cline{2-6}  & **M** & **M-SPI** & **M-hSPI-B** & **M-hSPI-N** & **M-hSPI-T** \\ \hline Rice flour, g & 50 & 40 & 40 & 40 & 40 \\ Quinoa flour, g & 50 & 50 & 50 & 50 & 50 \\ SPI, g & - & 10 & - & - & - \\ hSPI-B, g & - & - & 10 & - & - \\ hSPI-N, g & - & - & - & 10 & - \\ hSPI-T, g & - & - & - & - & 10 \\ Sugar, g & 65 & 65 & 65 & 65 & 65 \\ Oil, mL & 40 & 40 & 40 & 40 & 40 \\ Baking powder, g & 5 & 5 & 5 & 5 & 5 \\ NaCl, g & 1 & 1 & 1 & 1 & 1 \\ Xanthan gum, g & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 \\ Water, g & 85 & 85 & 85 & 85 & 85 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Formulation of batter used to obtain gluten-free muffins (M—control muffin; M-SPI—muffins enriched with soy protein isolate; M-hSPI-B—muffins enriched with soy protein hydrolysate produced with bromelin; M-hSPI-N—muffins enriched with soy protein hydrolysate produced with Nethurase; M-hSPI-T—muffins enriched with soy protein hydrolysate produced with trypsin).  
The moisture content was determined using the method SR 91:2007 [12]. The muffin height was estimated by measuring, with a caliper, the distance between the flat bottom surface to the highest point of each sample. The specific volume (cm\({}^{3}\)/g) of the muffins was determined by the rapeseed displacement method (SR 91:2007, [12]).  
The texture of the muffin samples was assessed by measuring the firmness of the crumb with the MLFTA apparatus (Guss, Strand, South Africa) and a probe of 7.9 mm in diameter. For each tested formulation, two samples were penetrated for 25 mm in three different points, at a penetration speed of 5 mm/s and a trigger threshold force of 20 g [15].  
The CIElab color parameters of the muffin crust in crumb, in terms of the brightness/darkness (L*), redness/greenness (a*) and yellowness/blueness (b*), were measured using the Chroma Meter CR-410 (Konica Minolta Business Solutions Europe GmbH) color-orimeter. In agreement with [PERSON] et al. [16], in order to evaluate the effect of soy proteins' or peptides' addition on the color appearance parameter of the muffin samples, the chroma (C*) and hue angle (H) were calculated using Equations (2) and (3):  
\[\mathrm{C}^{*}=\sqrt{\mathrm{a*^{2}+b*^{2}}} \tag{2}\]  
\[\mathrm{H}=\tan^{-1}(\mathrm{b*/a*})\text{ for quadrant I (+a*, +b*)} \tag{3}\]  
The antioxidant activity of the muffin samples was determined, as described by [17], using the ABTS+ and DPPH radical scavenging activity (ABTS-RSA and DPPH-RSA, respectively) methods. In short, the muffin samples were subjected to extraction in 80% aqueous methanol solution, for 2 h at 23 \(\pm\) 2 \({}^{\circ}\)C. The extracts obtained upon centrifugation for 15 min at 10,000 rpm were further used for measuring the antioxidant activity. ABTS-RSA was determined by measuring the absorbance of a mixture consisting of a 40 \(\mu\)L extract and 2.96 mL ABTS+ solution, at a wavelength of 734 nm, immediately and after 6 min. DPPH-RSA was determined by measuring the decrease, over 20 min, of the absorbance, at a wavelength of 515 nm, of a mixture consisting of a 100 \(\mu\)L extract, 250 \(\mu\)L DPPH solution and 2.1 mL of 80% aqueous methanol solution. In the case of each method, a Trolox standard curve was prepared, and the antioxidant activity was expressed as umol Trolox/g d.w.  
The baking experiment was carried out in duplicate, and the measurements were performed at least in triplicate.