Does UV-irradiation increase or reduce the level of phenolic compounds like flavonoids and alkaloids in a plant extract?
Products as quercetin and resveratrol are largely increased, but I suppose that the effect is not general. It will depend on the particular compound and plant
Indeed it depends on the class of compounds and the plant metabolic response (type of plant, plant health, organ sampled). In grapes UV irradiation has been shown to increase flavonoids/stilbenes etc.. (some are genotypic development responses, some are environmental e.g. GxE responses) -- however over-irradiation will lead to damage or in grape berries over-ripening results in colour bleaching and phenolic losses. Alkaloids I suspect, not certain, are more responsive to herbivory, wounding etc.. -- as they are generally toxic protectants. Best wishes.
UV radiation might be reduced some of the antioxidant present in medicinal plants. Thus in many publication authors suggest to dry the plant materials in shed in absence of Sun light, might be because it reduces the potential of active ingredient.
Your question is not absolutely clear. Will you irradiate the plant organ/tissue or the extract itself? If the purpose is irradiating the organ/tissue, the most likely to occur is an increase in the bioactive compounds, since most of the methabolic processes are still active. If you are considering irradiating a plant extract, the bioactive compounds are expected to decrease (unless the extract contain polymeric components, such as tannins, which are commonly found in lignified tissues).
The question is not clear. In general, and with regard the bioactive compounds I agree with Dr Barreira. If you dry plant material better do it in shed.
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