Processes for the separation and purification of polyphenol trans-resveratrol and/or anthraquinone emodin from Polygonum cuspidatum and/or Rumex acetosa, by means of solvent selective extraction. Products obtained by this process present high level of purity; being therefore useful in the preparation of nutraceutical (pharmaceutical and/or food) compositions with antioxidant, anti-inflammatory, antiviral, cardioprotective, neuroprotective, chemoprotective activities, besides protecting against infections and ischemia, treating type 1 and 2 diabetes, reducing obesity and preventing aging. Useful phytomedicines for the same therapeutic activity and prepared from the roots and/or rhizomes of Rumex acetosa or from their fractions are also provided.