## 4 Discussion
Our quick search in Scopus (accessed: January 2020) showed 188 records reflecting the number of articles that were published in 2018 (about 15.7 per month) and contained the following exact words as queries \"bioactive peptides AND food proteins\". The same query words were used to the search for the articles published in 2019. This simple search showed 241 papers published in 2019 (i.e., 20.08 per month). Both searches were limited to articles, and they excluded conference abstracts. Thus, it may appear that there are some biological activities represented by both parent peptides and their bitter-tasting motifs that were published after this paper was released,and thus, they were not included when we ran these studies. A similar search for the latest publications concerning sensory peptides showed no new sequences with confirmed bitterness that could be downloaded to the BIOPEP-UWM database and used for further analyses. Thus, our results concerning the presence of bitter-tasting motifs in parent sequences seemed to be relatively steady. Nevertheless, it is recommended to carry out the regular update of databases [38], as well as to use curated databases, like, e.g., BIOPEP-UWM [12]. Experimental issues that possibly affect the differences between in silico and in vitro results may be related to the hydrolysis of protein. Theoretical hydrolysis via bioinformatic tools, including BIOPEP-UWM, is based on the specificity of an enzyme, and hypothetically, all peptide bonds are accessible to enzymatic cleavage [58]. The cleavage of peptide bonds is one of the descriptors characterizing the nature of the enzyme [59]. However, the effectiveness of enzymatic hydrolysis depends also on the temperature, the pH, the enzyme-to-substrate ratio [46], and the types of the molecules affecting the inhibition of the enzyme [60], which are difficult parameters to be included as the \"elements\" of programs serving for theoretical proteolysis. Moreover, such predictive hydrolysis is relatively simple, especially when the protein is not chemically modified. For example, glycosylated amino acids present in a protein may block the breakdown of a peptide bond in experimental conditions [61]. Additionally, the computer simulation of hydrolysis does not consider the complexity of the protein structure that might hinder its interactions with proteolytic enzyme [58]. [PERSON] [62] added to this list some other factors likely to affect the results of proteolysis carried out in experimental conditions, i.e. : location of the enzyme and substrate in different extra- and intra-cellular regions and the involvement of inhibitors. They are not considered by programs for theoretical hydrolysis. In turn, [PERSON] [46] highlighted that proteolysis of soybean carried out in experimental conditions enabled the reduction of waste, establishing the mild conditions of reaction, avoiding unwanted reactions; however, the obstacle is the cost of enzymes, as well as the recovery and/or removal of bitter taste [46]. Despite the discrepancies between the in silico and in vitro results of the hydrolysis of proteins aiming to produce biopeptides, scientists use the hybrid approach more often [63]. [PERSON] et al. [9] applied this protocol to hydrolyze milk protein concentrate using exact enzymes as in the study above. They showed that the results of experimental and theoretical analyses differed. Twenty-eight peptides with the potential to affect the bitter taste of hydrolysates were produced in laboratory conditions, which was consistent by ca. 12 % with computer simulations (226 parent peptides identified in silico). [PERSON] et al. [19] used the in silico/in vitro/ex vivo analyses to study the potential of salmon (_Salmo salar_) proteins as the source of ACE inhibitory peptides. To verify the in silico results in laboratory conditions, protein hydrolysis was carried out in vitro (with commercial enzymes) and ex vivo (using digestive juices from volunteers).