## 3 Results
### Identification of Peptides Likely to Be Bitter Derived from SPC Hydrolysates  
The results of identification of parent peptides in SPC hydrolysate samples are present in Table 3. The highest number of such peptides was identified in ficin and bromelin hydrolysates of SPC (five and four, respectively). Peptides derived from F-SPC matched the sequences originally encrypted in: 7S globulin (1 peptide), glycinin (1 peptide), and \(\beta\)-chain of \(\beta\)-conglycinin (3 peptides). In turn, in the case of B-SPC, parent peptides were matched glycinin and the \(\beta\)-chain of \(\beta\)-conglycinin (two peptides each). One parent peptide was reported in papain SPC hydrolysate (source: \(\alpha\)-chain of \(\beta\)-conglycinin), whereas no peptides were found in proteinase K soybean protein hydrolysate. To summarize, the most effective enzymes producing in vitro the highest number of parent peptides were ficin > bromelin > papain. One parent sequence, i.e., LIVILNG, was identified in both B-SPC and P-SPC and matched both chains of \(\beta\)-conglycinin analyzed. All parent peptides identified in SPC hydrolyses contained motifs both with and without the status of a bitter-tasting indicator. Taking into consideration 339 parent peptides as the total sum of the sequences predicted as identified after in silico hydrolysis of soybean proteins and 10 parent peptides in vitro identified in SPC hydrolyses, the compatibility of the in silico and in vitro results of peptide identification was ca. 2.95%. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Time Interval (min)**} & \multicolumn{3}{c}{**Relative Area of Chromatographic Peaks (\%) 1**} \\ \cline{2-6}  & **0-SPC 2** & **B-SPC** & **F-SPC** & **P-SPC** & **PK-SPC** \\ \hline
14.00–39.99 & 50.1 & 83.3 & 96.7 & 93.6 & 85,2 \\
40.00–60.00 & 49.9 & 16.7 & 3.3 & 6.4 & 14.8 \\ C 3 & 0.0 & 4.0 & 14.2 & 6.8 & 2.4 \\ \hline \hline \end{tabular}  
* The area of all peaks between 14 and 60 min is 100% (See Figure 1); 2 0-SPC, B-SPC, F-SPC, P-SPC, PK-SPC: non-hydrolyzed soy protein concentrate, soy protein concentrate hydrolyzed by bromelin, ficin, papain, or proteinase K, respectively (see the Materials and Methods); 3 Calculated according to Equation (1).  
\end{table} 
Table 2: Results of soybean protein hydrolysis as revealed by RP-HPLC (Reversed-Phase High Performance Liquid Chromatography). Parent peptides were considered as identified in SPC hydrolysate if (a) the fragment ions were observed in the particular retention time (t\({}_{\text{R}}\)) and (b) t\({}_{\text{R predicted}}\) and t\({}_{\text{R experimental}}\) differed within the range of \(\pm\)10% [19; 22]. Peptide identification was understood as detection of a group of fragment (daughter) ions eluted in the same retention time [19; 22; 23]. Some of them could be formed via the non-sequential charge-directed pathway, leading to their formation by loss of water or the ammonia neutral molecule [24]. An example of a parent peptide that was identified in SPC hydrolysate fulfilling the above-mentioned criteria was the **FFE**ITPEK sequence (Figure 2) containing two bitter-tasting indicators: **FF** and **EL**. The **FFE**ITPEK was identified in an F-SPC sample and matched the \(\beta\)-chain of \(\beta\)-conglycinin. The m/z of the precursor (M+H)\({}^{+}\) ion was 1010.500 Da. An intensive peak was observed in t\({}_{\text{R experimental}}\) =36.200 min (t\({}_{\text{R predicted}}\) = 35.950 min). Moreover, the detection of this peptide in an F-SPC sample was confirmed by the presence of eight fragment ions that eluted within the above-mentioned time. They were as follows: X\({}_{4}\)\({}^{+}\), C\({}_{4}\)\({}^{+}\), B\({}_{8}\)\({}^{+}\), B\({}_{7}\)\({}^{+}\), B\({}_{6}\)\({}^{+}\), As\({}^{+}\), Z\({}_{7}\)\({}^{+}\), and Y\({}_{5}\)\({}^{+}\), and their intensity was expressed from several hundred (Y\({}_{5}\)\({}^{+}\) ion) to thousands of counts (kCounts; all other fragment ions).