negatively charged amino acid residues and hydrophobic amino
acids. So when ethanol was at a lower concentration, the charged
amino acids might be dominant to enhance the umami taste, and
when the ethanol concentration was elevated, hydrophobicity
increased thereby bitter taste might be improved.
However, from Table 5, the ratios of umami amino acids in peptides
to total umami amino acids were 59.47%, 61.29%, 95.44%, and
94.92% for soy sauce, XAD-0%, XAD-20%, and XAD-40%, respectively.
According to the finding that the umami taste of peptide
resulted from umami (or acidic) amino acid (Asp or Glu)
(Temussi, 2012), the umami taste of XAD-20% and XAD-40% might
be stronger than that of soy sauce and XAD-0%. And thus, the tastes
of XAD-0%, XAD-20% and XAD-40% fractions were doubtful and
needs for further study.