The amide A is attributed to both OH and NH stretching vibrations,
and reflects mainly the existence of H-bonds. Moreover, it
has been reported that if the N–H group of a peptide is involved
in a hydrogen bond, the amide A position is shifted to lower frequencies
(Doyle, Blout, & Bendit, 1975). Accordingly, salmon connective
tissue presented a broad absorbance with maximum
values ranging from 3287.8 cm1 in WP and 3281.8 in FP (Fig. 1).
The higher frequency in WP connective tissue, as denoted by the
peak frequency and the band amplitude, is indicative of a larger
N–H group of peptides involved in hydrogen bonds.