The UP consisted essentially of ACN-soluble compounds including non-polar or less-polar compounds. As expected, the IP and LP contained the most part of proteins (about 1.09 ± 0.19 mg and 3.29 ± 0.26 mg of proteins per gram of dried extract, respectively), where very low protein content was detectable in UP fraction (about 0.35 ± 0.03 mg/g of dry weight, DW, of extract). Phenol compounds were detected in all the three fractions, the most part being in the LP (about 520 μg of gallic ac. equivalents/g of dried extract) compared to UP and IP fractions (245 μg/g DW and 221 μg/g DW of extract, respectively). All the three fractions showed considerable antioxidant activity correspondent to 865, 1433 and 6294 nmol of Trolox equivalents (TE) per gram of dried sample in UP, IP and LP, respectively. The most antioxidant activity appeared related to the LP, since its value remained higher compared to the other fractions also when normalized to proteins or total phenols content (Figure 4C1–C3). Since the LP showed the highest content of both proteins and phenols, the nature of the antioxidant compound(s) cannot be identified at this level of analysis.
The absorbance spectra of the three fractions measured in the visible and far-red region (Figure 5) showed that the absorption properties of the UP correspond to the characteristic absorption spectra of the photosynthetic pigments (chlorophylls and carotenoids) and pigment-protein-complexes recognized in polar organic solvent [45,101]. The fractions showed high absorbance from 215 to 280 nm where peptide bonds in proteins and free amino acids have maximum absorption