Application of Fourier Transform Raman Spectroscopy for Prediction of Bitterness of Peptides

Abstract

The potential application of Fourier transform (FT) Raman spectroscopy to predict the bitterness of peptides was investigated. FT-Raman spectra were measured for the amino acid Phe and 9 synthetic di-, tri-, and tetra peptides composed of Phe, Gly, and Pro. Partial least squares regression (PLS)-1 analysis was applied to correlate the FT-Raman spectra with bitterness intensity values (R(caf) and log 1/T) reported in the literature. Using full cross-validation, Model 1 based on the single spectral data set for the nine peptides yielded a high correlation coefficient for calibration (R = 0.99), but a low correlation coefficient for prediction (R = 0.56). Two models were constructed using the data sets including replicate spectra for the calibrations and were validated using full cross-validation. Using leave-one-sample-set-out calibrations, Model 2, which was developed with the data for the peptides as well as Phe, yielded a low correlation coefficient (R = 0.533) for the prediction of the bitterness, while Model 3 developed with only the peptide data provided better correlation coefficients (R = 0.807 and 0.724 for R(caf) and log 1/T values, respectively). The correlation coefficients for prediction were 0.975 (R(caf) values) and 0.874 (log 1/T values) for Model 4, which was developed using subtracted spectral data (spectra of peptides with higher R(caf) values minus spectra of peptides with lower R(caf) values). Examination of the PLS regression coefficients at wavenumbers most highly correlated with bitterness revealed the importance of hydrophobicity and peptide length on bitterness. This study indicates the potential of FT-Raman spectroscopy as a useful tool for predicting bitterness of peptides and amino acids.

Structural characteristics of food protein-originating di- and tripeptides using principal component analysis

“…It may suggest that the presence of an additional amino acid ("Aa") in a tripeptide sequence could intensify its bitterness, which can be explained by the use of chemometric methods like PCA. For example, peptides GGF and GGY were found as bitter like GG-Aa type peptides due to the presence of bulky and high molecular weight residues [34], which was also observed in our PCA results (see Table 3). …”

“…Relatively high molecular weight of a given amino acid resulted also from the increasing number of carbon and hydrogen atoms, which was also revealed in the obtained PCs. Kim and Li-Chan [34] reported that high molecular weight of amino acids had the impact on peptides' bitterness, which also influenced their hydrophobicity. Peptides composed of F and/or Y (with a relatively high molecular weight) were reported to be bitter [34].…”

“…Kim and Li-Chan [34] reported that high molecular weight of amino acids had the impact on peptides' bitterness, which also influenced their hydrophobicity. Peptides composed of F and/or Y (with a relatively high molecular weight) were reported to be bitter [34]. Our two datasets contained peptides possessing an amino acid with ring (F, Y and/or P).…”

“…When looking at their bitterness measure-Rcaf. value defined as the ratio of bitterness to 1 mM caffeine solution; Rcaf = 1.0 [34]-the peptides with GG-Aa sequences ("more bitter") had Rcaf. between 0.03 (GGV) and 0.67 (GGY).…”

Understanding the nature of bitter-taste di- and tripeptides derived from food proteins based on chemometric analysis

“…They found that the presence of bulky C‐terminal amino acid in a peptide sequence affected its bitterness. When looking at the sequences of dipeptides analyzed, we reported that they were composed mostly of amino acids with branched and bulky side chains (both N‐ and C‐terminal) like, for example, L, I, V, G, and F. The presence of branched side chains or ring affected the molecular weight of a whole peptide (Kim & Li‐Chan, ). The analysis of di‐ and tripeptide data sets indicated that most of di‐ and tripeptides possessed N‐ or C‐terminal residues with a cyclic and/or aromatic ring like P, F, and Y.…”