Nature is a valuable source of anti-oxidants that have a health-promoting effect by inhibiting various undesirable changes leading to cell degradation and, consequently, potential disease ailments. One of them is gallic acid which has been used as a healing agent since ancient times. Currently, due to various beneficial properties, this compound is considered to be one of the main phenolic acids of great importance in numerous industries. It is commonly used as a substance protecting against the harmful effects of UV radiation, an astringent in cosmetic preparations, and a preservative in food products. Therefore, gallic acid is now deemed essential for both human health and industry. Increasingly better methods of its isolation and analysis are being developed, and new solutions are being sought to increase its production. This review, presenting a concise characterization of gallic acid, updates the knowledge about its various biological activities and methods used for its isolation and determination, including chromatographic and non-chromatographic methods.

Negative impact of radicals on humans and animals is responsible for growing research interest in antioxidant properties of substances, which protect living organisms from the damaging influence of these reactive species. Among numerous methods for antioxidant activity estimation, DPPH and ABTS are the most popular and commonly used ones due to their ease, speed, sensitivity and the usage of stabile radicals. The paper shows and discusses the antioxidant properties of a few compounds exhibiting different extinction of the wavelength used to monitor colored radical depletion in spectrophotometric measurements—e.g. 516 and 744 nm in DPPH and ABTS assays, respectively. As results from the presented data, the difference between true and spectrophotometrically estimated IC₅₀ values for colored antioxidants depends not only on extinction coefficient of the monitored wavelength by the antioxidant but also on its remaining concentration in the measuring system. The presented results seems to be helpful for the researches examining coloured antioxidants and plant extracts containing substances having spectra in Vis region.