Oxidative stress is a well-known phenomenon arising from physiological and nonphysiological factors, defined by the balance between antioxidants and pro-oxidants. While the presence and uptake of antioxidants are crucial, the pro-oxidant effects have not received sufficient research attention. Several methods for assessing pro-oxidant activity, utilizing various mechanisms, have been published. In this paper, we introduce a methodology for the simultaneous determination of antioxidant and pro-oxidant activity on a single microplate in situ, assuming that the FRAP method can measure both antioxidant and pro-oxidant activity due to the generation of pro-oxidant Fe²⁺ ions in the Fenton reaction. Systematic research using this rapid screening method may help to distinguish between compounds with dominant antioxidant efficacy and those with dominant pro-oxidant effects. Our preliminary study has revealed a dominant pro-oxidant effect for compounds with a higher number of oxygen heteroatoms, especially sp2 hybridized compounds (such as those containing keto groups), such as flavonoids and plant extracts rich in these structural types. Conversely, catechins, carotenoids, and surprisingly, extracts from birch leaves and chestnut leaves have demonstrated dominant antioxidant activity over pro-oxidant. These initial findings have sparked significant interest in the systematic evaluation of a more extensive collection of compounds and plant extracts using the developed method.

Salvia is a widely used herb that also contains essential oils and other valuable compounds. In this work, the hydrolates of five Salvia sp. were evaluated for their potential antimicrobial and antioxidant activity against four bacterial strains. The hydrolates were obtained from fresh leaves by microwave-assisted extraction. Chemical composition analysis by gas chromatography and mass spectrometry revealed that their major constituents were isopulegol (38.2–57.1%), 1,8-cineole (4.7–19.6%), and thujone (5.6–14.1%). The minimum inhibitory concentration (MIC) of the plant hydrolates was tested by the microdilution method at concentrations ranging from 1.0 to 512 μg/mL. The hydrolates prepared from Salvia officinalis and S. sclarea showed inhibitory activity on the tested Gram-positive and Gram-negative bacteria, taxon Salvia nemorosa showed inhibitory activity only partially. The hydrolate of S. divinorum had practically no antibacterial effect. Enterobacter asburiae was the only bacterium for which we found sensitivity to the hydrolate of S. aethiopis, with a MIC50 value of 216.59 µL/mL. The antioxidant activity of the hydrolates was low, ranging from 6.4 to 23.3%. Therefore, salvia hydrolates could be used as antimicrobial agents in medicine, cosmetics, and food preservation.

Euglena gracilis is a flagellate photosynthetic microalga that, thanks to its metabolic adaptability, can grow under both autotrophic and heterotrophic conditions. This adaptability makes euglena an interesting species for applied biotechnology. We focused on the proteome of E. gracilis cultivated in Cramer-Myers medium (supplemented with ethanol) in dark and light conditions. Cultures grown in the light showed a characteristic green coloration, while cultures incubated in the dark were bright yellow. When cultured in the dark, microalga showed reduced concentration of chlorophylls (a, b, and total) and carotenoids compared to cells cultured in the light. Conversely, there was an increase in proline content in the dark compared to light cultivation. Using proteomic approach, we revealed 162 differentially accumulated proteins in light- and dark-grown cells classified into 12 functional groups. Notably, alterations in the metabolism of fatty acids and amino acids, secondary metabolism, and accumulation of stress- and detoxification-related proteins in microalgal cells cultivated in darkness with ethanol as a carbon source may help euglena adapt to these conditions. Based on our results and literature, we hypothesize that vitamin B12 potentially plays an important role in light/dark metabolic switch, similarly as in bacteria.

Oxidative stress reflects an imbalance between pro-oxidants and antioxidants arising from physiological or environmental factors. Here, we applied our previously developed in situ microplate method for the simultaneous determination of antioxidant and pro-oxidant activities to compounds produced by plant cell cultures in vitro. The primary aim was to evaluate the added value of these compounds, which are widely used as additives in food, cosmetic, and pharmaceutical products. The secondary aim was to assess whether a predominance of pro-oxidant activity could limit their biotechnological production. Thirty-three compounds known to be produced by in vitro cultures (polyphenolic acids, flavonoids, quinones, alkaloids, etc.) were tested, and the pro-oxidant–antioxidant balance index (PABI) was calculated. Sixteen compounds showed measurable activities with DPPH₅₀/FRAP₅₀ values below 2 mM. Within this set, rosmarinic acid exhibited pronounced pro-oxidant behavior, whereas gallic acid, chlorogenic acid, and the anthocyanin cyanidin showed higher antioxidant potency and favorable PABI values. Such compounds may deliver added benefits when incorporated into food or cosmetic products and are unlikely to limit production in cell culture.