200 M.V. Moreno-Arribas et al.
Fig. 6B.3UV, original and first and second derivative spectra of four glycylpeptides (from
Bartolom ́e et al. 1997, with permission)
6B.2.6 Determination of Amino Acid Composition and Sequence
in Peptides
The amino acid composition of peptides is generally assayed by carrying out acid
hydrolysis with 6 M hydrochloric acid, followed by determination of the individual
amino acids by HPLC. Various types of HPLC have been employed to separate
amino acids, but reversed-phase chromatography on C 18 columns is the most com-
monly system used. Detection of amino acids normally involves derivatization, since
their maximum absorbance is at 214 nm in which many other compounds also can
absorb. The most frequently used derivatizing agents are dansyl chloride, phenyl
isothiocyanate ando-phthaldialdehyde.
Peptide sequencing is normally performed by degradation of the N-terminal
amino acid using phenyl isothiocyanate (Edman’s reagent). The terminal amino
groups react with the isothiocyanate, forming a phenylthiocarbamylic derivative.
After its treatment with acid in an organic solvent, cyclization takes place forming
the phenylthiohydantoinamino acid that canbe separated from the rest of the chain,
which remains intact, and the process can be repeated.
6B.3 Origin and Peptide Characterization
There are very few studies focused on determining the origin, concentration and
composition of wine peptides. These studies have been carried out on peptide
fractions of different molecular weights that have been obtained with different