Determination of tannin content—The tannin
content of the TSCEs was examined by measuring
their adsorption on standard hide powder. Briefly,
the amount of total phenol content (A1) in TSCEs
was determined using Folin-Ciocalteu method as
previously described and the amount of phenol not
adsorbed by the hide powder was measured (A2). The
pyrogallol was used as standard (A3) and the
percentage of tannin content expressed as pyrogallol
was calculated by the following equation: