The pH of the sample was adjusted to 2.0
with HCl (1 mol/L). Subsequently, the material was stored for
24 h at 5 C, protected from light. After this period, the material
was filtered and the extract was centrifuged at 2000 rpm for
10 min. The supernatant was filtered on Whatman paper # 1 and
the resulting extract was neutralized to pH 7.0 with NaOH
2.5 mol/L.