INTRODUCTION
Antioxidants are the main regulators of free radical transformations in the body. Therefore, antioxidant activity is currently one of the most important and sought-after characteristics of substances. Our research consists in its determination by optical spectrophotometry based on the reaction with diphenylpicrylhydrazyl (DPPH). The main object of our research are extracts from natural raw materials, namely tree bark extracts.

In the process of metabolism, reactive oxygen species (ROS) are formed and accumulated in the cell. They play a dual role in the human body. On the one hand, being signal molecules, they serve to build and renew the structural elements of cell membranes. On the other hand, an excessive amount of ROS, which are radicals in nature, can lead to the oxidation of important organic molecules in the body and cause cell and gene mutation. Thus, ROS cause destructive reactions in the body, contributing to the emergence of many diseases and accelerating the aging process of the body.

The regulation of oxidation processes and the level of ROS accumulating in the cells of the body is carried out by the antioxidant system. Oxidative stress develops when the human body is exposed to adverse environmental factors, increased physical and emotional stress, as well as long-term illnesses and aging. The antioxidant system ceases to cope with its function as a regulator of the content of oxidants, cannot completely suppress excessive oxidation reactions, therefore, it becomes necessary to introduce additional substances with antioxidant properties into the human body.

To do this, it is necessary to have information both about the state of the antioxidant system of the body and about the antioxidant activity (AOA) of the drugs taken, dietary supplements, food and drinks. Therefore, the study of plant extracts as natural sources of antioxidants is an urgent task today.

There are a number of methods for determining antioxidant activity. To date, optical, electrochemical and chromatographic methods of research are most widely used. Among the existing methods for studying AOA, optical methods should be noted as the most simple and informative.

MATERIALS AND METHODS

The object of the study are extracts from natural raw materials produced by ARAL LLC in the Sverdlovsk region: extracts of larch (lat. larix), pine (lat. pinus) and cedar bark (lat. cedrus), chaga extract (lat. inonotus obliquus), as well as a mixture of pine bark extract and chaga extract. The state standard sample of quercetin was used as the reference drug; In order to more visually display the results of the study, a comparison was also made with rosehip extract, which is widely used in nutrition. The study of AOA was carried out by a spectrophotometric method based on the reaction with diphenylpicrylhydrazyl (DPPH).

Stock solutions of the studied extracts were prepared by diluting 100 mg of the extract in 100 ml of hot non-boiling water. The concentration of the resulting solution is 1 mg/ml. Working solutions of the extracts were obtained by diluting the stock solution. The final concentrations of the studied extracts were 10, 20, 50, 100, and 200 μg/mL. In the case of rose hips, final concentrations are 10, 50, 100, 200, 500 and 800 µg/ml.

A solution of quercetin was prepared by diluting 2 mg (exactly weighed) of quercetin in 20 ml of 95% ethanol. The concentration of the resulting solution is 0.01 mg/ml. Working solutions of quercetin were prepared by diluting the stock solution; final concentrations were 0.2, 0.5, 1, 2, 5, and 10 μg/mL.

A solution of DPPH was prepared by diluting 2 mg (accurately weighed) of DPPH in 50 ml of 95% ethanol, the tube was wrapped in aluminum foil and removed in a dark place. The concentration of the resulting solution is 0.04 mg/ml.

The analyzed samples consisted of 0.5 ml of the working solution of the corresponding extract or quercetin, 1.5 ml of the ethanol solution of DPPH (concentration 0.04 mmol in 95% ethanol) and 1.5 ml of 95% ethanol.

The control sample for the study of extracts consisted of 0.5 ml of filtered boiled water, 1.5 ml of DPHG ethanol solution and 1.5 ml of 95% ethanol. To determine the AOA of quercetin, the control sample consisted of 1.5 ml of an ethanol solution of DFPG and 2 ml of 95% ethanol. The samples were kept for 30 minutes in a dark place, after which the optical density was measured on a PE-5400UF spectrophotometer (Ekohim LLC, St. Petersburg) at a wavelength of 517 nm. Based on the obtained values of the optical density of the analyzed samples, the percentage of DPH inhibition was calculated. The value of inhibition of the DPH radical (in %) was calculated as the ratio of the difference in the optical density of the control and analyzed samples to the optical density of the control sample.

The AOA of the release of extracts and reference drugs (quercetin) is evaluated by IC50, the goal is to use the substance (μg / ml), at which 50% reduction of the DPPH radical occurs. This value was found by calculating a trend line that approximates our results.