Testing the effects of drying methods on willow flavonoids, tannins, and salicylates

In this study, we compared the effects of several preservation methods on t he secondary phenolics of the mature leaves of purple willow (Salix purpure a L., Salicaceae) with results obtained with fresh leaf analyses. Conventio nal freeze-drying, in which the leaves were first frozen with liquid nitrog en and then placed in a freeze-dryer, produced substantial qualitative and quantitative changes in purple willow flavonoids and salicylates. Modified freeze-drying, in which leaves were put into a freeze-dryer without being p refrozen, gave concentrations that, for most secondary components, were com parable with those found in fresh leaves. Reducing the freeze-dryer chamber temperature hindered the decomposition of phenolics in prefrozen leaves an d in leaves dried without prefreezing. Heat drying induced substantial chan ges in the composition of all phenolics, except for apigenin-7-glucoside. V acuum drying at room temperature gave the highest concentrations for nearly all phenolics, while room-drying with desiccation gave results that were c omparable with those obtained by fresh leaf analyses.