## 1 Introduction  
The enormous interest in natural sources of phytochemicals, which have potential benefits for improving health and combating some socially significant diseases, is noticeable. Horse chestnut (_Aesculus hippocampus_ L.) from the family Hippocastanaceae, which is a native to Europe is known to have various medicinal and health benefits obtained from the numerous phytoconstituents present in its seed [1]. _Hippocamp_ L. has been widely used for centuries in traditional medicines as a cure for several diseases and disorders, such as chronic venous insufficiency, hemorrhhod disease, traumatic edema, etc. [2, 3]. Its extracts, whose main bioactive components are saponins, flavonoids, tannins, alkaloids,glycosides, triterpenoids, steroids, and phenolic substances, have various beneficial effects, including anti-inflammatory, venotonic, and vascular protective effects, as well as immunotherapy, anticarcinogenic, antibacterial and antioxidant activity [2; 3; 4; 5]. The biological activity of horse chestnut allows its widespread use in the pharmaceutical and cosmetic industry. Moreover, the horse chestnut finds various applications as a valuable resource in industry [2; 5]. Some studies evaluated the biochemical composition and the biological activity of horse chestnut from different areas. _Hippocampatanum_ L. seeds are natural products whose chemical composition is very complex, since they contain a lot of different molecules. The majority of them are polysaccharides (both starches and non-starches), lipids, proteins, and essential mineral elements, such as nitrogen, phosphorus, calcium, copper, iron, zinc, etc., and many minor components among others [2; 6]. According to the literature, significant differences in the phytochemical composition and antioxidant activity of extracts obtained from different organs of the plant (bark, fruits, leaves, flowers, seeds), and also between separate parts of the seed-coat and endosperm were observed. The data obtained on the content of polyphenols are the following: in horse chestnuts leaves (7.81-24.48 mg/g FW), seeds (24.24-70.40 mg/g FW), flowers (8.17 mg/g), and bark (363.58 mg/g FW) [7]. Previously published data indicated relatively strong antioxidant properties of horse chestnut seed coat extracts and significant absorbance in the ultraviolet range, suggesting their potential utility against UVB-induced DNA damage [8; 9]. On the other hand, in order to prevent natural products from developing pathogenic microorganisms and thus prolonging their shelf-life time, they require disinfection. In the past, the fresh chestnut fruits were fumigated with methyl bromide after harvest to comply with the international phytosanitary regulations for pest quarantine [10]. But its use has been prohibited in Europe (following a 239 European Scientific Journal December 2013/SPECIAL/edition vol.3 ISSN: 1857-7881). The treatment of chestnut by gamma rays could be a feasible alternative for disinfection, since the technology has proven itself to be in practice easy, fast, cheap, reliable, and reducing spoilage losses and it was approved by international organizations of food (FAO--Food and Agriculture Organization) and health (WHO--World Health Organization). The increasing application of gamma treatment to natural products in order to improve their hygienic qualities requires study of the impact of high-energy radiation on their chemical composition and bioactivity. Previous studies of plant-based products established a correlation between gamma treatment, chemical composition, and antioxidant capacity [11; 12]. It is known that as a result of the irradiation various radical structures are formed in the substances. Some radicals quickly recombine, but others are relatively stable because of the trapping in the solid phase of substances. These radicals and their decay could be detected and analyzed by EPR spectroscopy, which is a highly sensitive technique for the detection of paramagnetic organic and inorganic substances.