PRESERVING LEAVES FOR TANNIN AND PHENOLIC GLYCOSIDE ANALYSES - A COMPARISON OF METHODS USING 3 WILLOW TAXA

Members of the Salicaceae often produce phenolic glycosides and conden sed tannins. There is much debate on the best method for the preservat ion of leaf material prior to chemical analysis. Published results ind icate freeze-drying, a method commonly used for tannin analysis, may b e inappropriate for phenolic glycosides, unless done in a manner to pr event thawing during the drying process. Another commonly employed met hod, air-drying, is appropriate for phenolic glycosides but inappropri ate for condensed tannins. I present evidence using willow leaves that demonstrates that: (1) leaves freeze-dried in external flasks without temperature control contain lower concentrations of phenolic glycosid es (salicortin and 2'-cinnamoylsalicortin), (2) air-dried leaves have reduced concentrations of condensed tannins, while (3) vacuum-dried fr esh leaves have high concentrations of both phenolic glycosides and co ndensed tannins. Freeze-drying caused salicortin and 2'-cinnamoyl sali cortin concentrations to drop by 20 mg/g and 4 mg/g, respectively. Sal icin, a product of salicortin and 2'-cinnamoyl salicortin degradation, is absent in vacuum-dried leaves, present in air-dried leaves and ver y high in freeze-dried leaves. Thus, the presence of salicin in this s ystem is an artifact of the preservation technique. Condensed tannin c oncentrations dropped nearly 20 mg/g when leaves were air-dried. Thus, vacuum-drying fresh leaves allows researchers to quantify phenolic gl ycosides and condensed tannins from the same leaf material.