## 4 Discussion
The results of the enzymatic release of a fragment containing bitter-tasting motifs with and without the status of an indicator are presented in Table 1. This way of data analysis fits the research trend of fragmentomics relying on ascribing the \"unknown\" biological function of a molecule to the known function of motifs occurring in it and is based on positive selection (see above) [7; 39]. In our study, the molecule with no predicted function was a compound called the parent peptide, whereas the motif deciding its possible function was the bitter-tasting peptide. Thus, to be consistent with the fragmentomic idea, data analysis was limited to the released peptides composed of at least four amino acids. Data about the bitterness of such peptides were implemented from the BIOPEP-UWM database of sensory peptides and amino acids [20]. Based on the MLR stepwise regression analysis, some of these peptides were selected as bitter-tasting peptidic indicators, i.e., peptides with approximate predictedand experimental R\({}_{\text{caf}}\) values [13]. MLR is one of the chemometric techniques that enables analyzing the relationship between the structure (i.e., sequence) of a peptide and its biological activity, which is called QSAR (i.e., quantitative structure-activity relationship) [50]. According to [PERSON] et al. [51], the QSAR methodology is one of the important methods for the analysis of the functionality of peptides. The results of MLR showed that the bitter taste of a peptide is attributable to the presence of some specific residues, like Leu, Ile, Val, Phe, and Tyr [13]. This observation was consistent with the statements of other authors studying bitter peptides using QSAR techniques [52]. Ample in silico studies have been undertaken to evaluate proteins as sources of peptides with various bioactivities using the BIOPEP-UWM database [12]. The analysis of data concerning theoretical release of peptides can be considered from several perspectives, namely: how the length of motifs affects their match to the parent peptides; how the length of the parent peptide contributes to the presence of a bioactive motif in it; and finally, how the length of protein affects the number of parent peptides to be produced. As could be seen, parent peptides that were theoretically released from soybean proteins were the sources of bitter motifs with and/or without the status of an indicator. The great majority of such motifs were dipeptides. According to [PERSON] and [PERSON] [53], the match of the motif to the query sequence depends on its chain length (i.e., the shorter, the better). The potential of parent peptides as sources of peptides with a specified function can be quantitatively evaluated using the A parameter (see above). So far, the discriminant A had been successfully applied to compare proteins according to the rule: the higher the A value, the better source of biopeptides the protein of interest is [47]. As regards the parent sequences, no regularities were observed between their chain length and the increasing tendency in the occurrence of bitter-tasting motifs. An example in this case is the **DIFL/FL**, **IF** peptide (from \(\beta\)-conglycinin \(\beta\)-chain hydrolyzed with ficin). Its A value was 0.500. The ETSFHSEFEEIN peptide was derived from the same source as DIFL and contained two bitter-tasting motifs: **EI**, **EF**. Hence, its A value was 0.166. In the case of parent peptides, also their particular amino acid composition is crucial to predict their biological function including the likelihood of them to taste bitter. To exemplify it, these two criteria were fulfilled for parent peptide FSHNILETSFHEEF  
in silico method had to match those already present in the database [9]. The results of this work showed the successful identification of nine parent peptides in total (see Table 3) in all SPC hydrolysates, whereas the in silico simulation of hydrolysis of soybean sequences allowed obtaining 339 parent peptides.