بررسي تانن پوست درختان توسكا و بلوط به روش اسپكتروفتومتري

Spectrophotometrical Study on Barkʹs Tannin of Alder and Oak Trees

In this study, bark of alder (Alnus subcordata) and oak (Quercus castanifolia) were extracted by 1% alkali (1:10 w/v) at 90°C for one hour. Net yield of extractions were 21.44% for alder and 24.07% for oak. According to Stiasny number obtained for alder (90.28) and oak (70.02), the value of active polyphenolic compounds for the two species were estimated to be 19.35 and 16.85%, respectively. The amounts of condensed tannin were determined by column chromatography packed with sephadex LH-20 and found to be 6.3% and 4.2%, respectively. The results showed that condensed tannin in alder is 50% more than that in oak. The hydrolysable tannins (gallotannin and ellagitannin) were also estimated by spectrophotometry method. The high amount of ellagic acid in oak and alder extractives (respectively 43% and 35.3%), indicates that most of the tannin in these species are hydrolysable. In general, the bark of oak and alder contained 21% and 6.9% tannin, respectively.