Soybean (Glycine max) Protein Hydrolysates as Sources of Peptide Bitter-Tasting Indicators: An Analysis Based on Hybrid and Fragmentomic Approaches

Abstract

The aim of this study was to analyze soybean proteins as sources of peptides likely to be bitter using fragmentomic and hybrid approaches involving in silico and in vitro studies. The bitterness of peptides (called parent peptides) was theoretically estimated based on the presence of bitter-tasting motifs, particularly those defined as bitter-tasting indicators. They were selected based on previously published multilinear stepwise regression results. Bioinformatic-assisted analyses covered the hydrolysis of five major soybean-originating protein sequences using bromelain, ficin, papain, and proteinase K. Verification of the results in experimental conditions included soy protein concentrate (SPC) hydrolysis, RP-HPLC (for monitoring the proteolysis), and identification of peptides using RP-HPLC-MS/MS. Discrepancies between in silico and in vitro results were observed when identifying parent peptide SPC hydrolysate samples. However, both analyses revealed that conglycinins were the most abundant sources of parent peptides likely to taste bitter. The compatibility percentage of the in silico and in vitro results was 3%. Nine parent peptides with the following sequences were identified in SPC hydrolysates: LSVISPK, DVLVIPLG, LIVILNG, NPFLFG, ISSTIV, PQMIIV, PFPSIL, DDFFL, and FFEITPEK (indicators are in bold). The fragmentomic idea of research might provide a supportive method for predicting the bitterness of hydrolysates. However, this statement needs to be confirmed experimentally.

Characteristics of Biopeptides Released In Silico from Collagens Using Quantitative Parameters

“…It is worth mentioning that the computer simulation of proteolysis assumes that all peptide bonds are hydrolyzed in a protein chain. This issue is more complicated when hydrolyzing the protein in laboratory conditions, as described by Iwaniak et al [45,46] who hydrolyzed milk and soybean proteins as sources of bitter-tasting motifs using in silico and in vitro protocols.…”

“…Only one tripeptide, PGL-acting as the ACE inhibitor, was released due to the action of pepsin on the collagens derived from cow, pig, chicken, horse, and salmon. Short motifs, like di-and tripeptides, more easily match the sequence of the parent protein [45,46]. Considering the peptide sequences provided in Table 3, most of them were composed of the following amino acids: Pro, Phe, Gly, Leu, and Arg.…”

“…This strategy of research based on searching for biopeptides with known sequences in the protein that so far had not been known as their source is called a positive selection. Such an idea to study biopeptides from foods was applied by several authors [45,46,[49][50][51]. Thus, the next step in our study was to acquire the information about the peptides theoretically found in peptic and/or tryptic hydrolysates of collagens.…”

“…Collagen is rich in hydroxyproline which might be "not recognized" by programs serving for theoretical hydrolysis [65]. The additional factors which are "not considered" by programs for bioinformatic-assisted hydrolysis were discussed by Iwaniak et al [45,46] who applied the integrated approach for milk and soybean proteolysis. These factors included among others the complete characteristics of enzyme (optimal pH, temperature, enzyme-to-substrate ratio), complexity of protein structure, location of the enzyme and substrate in different extra-and intracellular regions, and involvement of inhibitors [45,46].…”

“…The additional factors which are "not considered" by programs for bioinformatic-assisted hydrolysis were discussed by Iwaniak et al [45,46] who applied the integrated approach for milk and soybean proteolysis. These factors included among others the complete characteristics of enzyme (optimal pH, temperature, enzyme-to-substrate ratio), complexity of protein structure, location of the enzyme and substrate in different extra-and intracellular regions, and involvement of inhibitors [45,46]. On the other hand, even if the proteolysis is incomplete, predicted peptides may be detected as judged during experiments carried out on milk [45] and soybean [46] proteins.…”