3.2. Determination of molecular masses for olive proteins by CGE
The twenty different varietal samples included in Table 1 were
analyzed by the CGE method optimized to determine the molecular
masses of the olive proteins. The analysis of the protein profiles
obtained by CGE showed seven peaks that were observed in most of
the olive varieties studied. Table 2 shows the migration times for
these seven peaks, the UV spectra, the number of olive varieties that
present the peak, the abundance of the peak considering the seven
selected peaks, the molecular masses calculated using CGE data, and
their tentative assignment to proteins already reported in literature.
Identification of some electrophoretic signals could be performed by comparison with the molecular masses previously
reported when using SDS-PAGE. Nevertheless, it is important to
highlight that the correspondence between SDS-PAGE and
SDS-CGE is tentative due to the different migration behavior of
proteins in both techniques. Just four signals with molecular
masses of 22.1 7 0.6, 307 1, 48 7 1, and 53 7 2 kDa, could be
assigned to proteins previously observed by SDS-PAGE. Indeed,
the fourth peak observed by SDS-CGE analysis showed a molecular mass of 22.1 7 0.6 kDa that could be related to a polypeptide
found by Alche´ [4] and derived from the precursor of 41 kDa. This
peak was present in 18 of the 20 analyzed varieties although its
abundance was very low (only 4.4%). The peak with a molecular
mass of 307 1 kDa could be attributed to a polypeptide of 30.0 kDa
[4,20]. The last two peaks had the worst resolution and could be
assigned to the same protein, an oleosin of 50 kDa reported by Ross
[9] and Esteve [20]. The rest of peaks were never observed using
SDS-PAGE with traditional extraction methodologies. Only a recent
work of the group using protein extraction with peptide ligand
libraries [15] enabled the detection of more SDS-PAGE bands that
could be correlated with the additional three signals observed in this
work by SDS-CGE. Finally, the last peak appearing at 17.7 min
presented the highest area (35.0%). Fig. 2 shows, as example, the
electropherogram corresponding to the olive variety ‘Alamen˜o de
Cabra’, presenting all common peaks, compared with the size
standards used to determine the different molecular masses.