R. Julkunen-tiitto et S. Sorsa, Testing the effects of drying methods on willow flavonoids, tannins, and salicylates, J CHEM ECOL, 27(4), 2001, pp. 779-789
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.