Tannin compounds were determined according to Makkar,
Blummel, Borowy, and Becker (2006). Two hundred microliters of
extract was mixed with 20 mg of insoluble polyvinylpolypyrrolidone.
After 15 min of incubation at 4 C, the tubes
were centrifuged for 10 min at 15,000 g. Then, 0.05 mL of supernatant
was used to determinate tannin content by the same
procedure used for total phenolic content. The tannin content was
the difference between the total and non-absorbed phenolics. The
results are expressed as milligrams of GAE per gram of extract (dw).