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Introduction: Prunus spinosa L. (blackthorn, sloe) is a com- mon species in the wild flora of Europe. Marmalade, syrup, and alcoholic beverages have been prepared from fruits. In folk medicine they'are used due to the astringent effect. However there are few studies on these indigenous fruits. According to the literature they contain tannins, anthocyanins, sugars, vitamin C etc., Methods: Our objective is to determine the antioxidant activity as related to their phenolic composition. For this purpose we prepared extracts using methanol, methanol-water (1: 1) and water. The antioxidant activity was determined by DPPH method and by photochemiluminescens (PCL) method. The total polyphenols, total anthocyanins and flavonoids were determined by colorimetric methods. Individual polyphenols were identified by a RP-HPLC-UVIVIS method., Results: The antioxidant activity decreased in the extracts as follows: methanol > methanol-water > water (IC₅₀= 1.33 mg/ml for DPPH; 11.94 μmol AAEIml for PCL > IC₅₀ = 1.87 mg/ml for DPPH; 10.35 μmol AAElml for PCL > IC₅₀ = 15.29 mg/ml for DPPH, 1.89 μmol AAElml for PCL) which is cor- related with the total polyphenol content (369 mg/100g > 244 mg1100g > 101 mg1100g) and total anthocyanin content (37.11 mg/100 g > 16.33 mg/100g > 7.76 mg/100g). The fla- vonoid content is similar in the three extracts (between 35.82 - 37.32 mg1100 g). The HPLC analysis shows high chloro- genic and neochlorogenic acid levels, followed by glycosides of quercetin., Conclusions: Our results demonstrated that blackthorn fruits are a rich source of phenolic compounds, with anti- oxidant activity, which are best extracted with methanol or methanol-water.

In the past years great importance has been attributed to antioxidant therapy in the prevention and treatment of disorders developed in connection with oxidative stress. After initial success, undesirable effects, toxicities, and prooxidant effects of antioxidants were reported [CARET, ATBC study]. In addition, metaanalyses failed to confirm the role of antioxidant supplementation in the primary and secondary prevention. The authors review the prooxidant effects of antioxidants, and their role in cell signalling and cell process modulation. Finally, the authors summarize possible explanations why combined use of antiooxidants is more favourable.

Medical science alongside with other sciences, aiming to preserve health and combat diseases, has evolved significantly since the late 1930s. It has reached incredible results and opened up unpredicted perspectives for future generations to come. From the 1980s significant results also emerged from researching natural plant active ingredients for the prevention of damage from free radicals which were discovered in different symptoms. One of the important areas of research is the recognition of significant bioactive molecules from the aspects of food consumption, alongside the detection of their effect in the context of their structure. It is also important that by possessing these data it is possible to develop correct food consumption habits, especially for people who are suffering from diseases. Through the decades we came a long way from folk medicine observations to molecular, biological justification of effect mechanisms.