PRESERVATION OF SALICACEAE LEAVES FOR PHYTOCHEMICAL ANALYSES - FURTHER ASSESSMENT

The chemistry of the plant family Salicaceae has been of interest to r esearchers as diverse as chemical ecologists, chemosystematists, and p aper chemists. Continuing the debate on proper methods for preservatio n of plant material prior to analysis, vacuum-drying was recently advo cated, because freeze-drying may cause degradation of phenolic glycosi des. This study was conducted to clarify the consequences of freeze-dr ying for foliar secondary chemicals and to evaluate the consequences o f vacuum-drying for primary compounds (protein and carbohydrates). Lea ves of quaking aspen (Populus tremuloides) were Bash-frozen in liquid nitrogen and freeze-dried or vacuum-dried at room temperature. We then analyzed samples for levels of salicortin and tremulacin (phenolic gl ycosides), condensed tannins, nitrogen, soluble protein, sugars, and s tarch. Freeze-drying did not alter the concentrations of phenolic glyc osides or tannins, relative to vacuum-drying. Freeze-drying did cause a small and inexplicable decline in nitrogen and soluble protein. Vacu um-drying, however, reduced starch concentrations by 38%. We suggest t hat the vacuum-drying method be used in studies in which carbohydrates are of no interest. For studies measuring carbohydrates, however, fre eze-drying is a better alternative, and should effect no changes in le vels of secondary compounds if samples are not allowed to thaw during the drying process.