Search

The bark resulted as a by-product after different Quercus sp. processing is a valuable alternative source of phenolic compounds (mainly tannins). Hence, the focus of the present work was to obtain eight extracts from the rhytidome of the less-studied Q. dalechampii and Q. frainetto and characterize them in terms of chemical and bioactive profiles. Ultrasound and microwave-assisted extraction methods were used for the preparation of the extracts. Total phenolic and tannin contents were assessed through classic spectrophotometric methods, while several individual phenolic compounds were identified and quantified using UPLC-PDA. Antioxidant, enzyme-inhibitory, antibacterial, and cytotoxic activities were tested using in vitro assays; additionally being evaluated was the ability of the extracts to inhibit the adherence of MRSA to suture wires. The UPLC analysis confirmed the presence of gallic acid, catechin, taxifolin, vanillic acid, epicatechin, and caffeic acid. The results showed that tested extracts were able to exert cytotoxic effects, at 6% and 3% concentrations, on confluent cells. The tested solutions inhibit α-glucosidase activity and the antibacterial potential suggested a mild to moderate effect against the Gram-positive strains. Overall, the obtained results revealed rich phenolic and tannin contents for the extracts obtained from both species through microwave-assisted extraction, probably responsible for their mild antibacterial and cytotoxic effects. [ABSTRACT FROM AUTHOR]

Quercus wood (oak wood) is a valuable resource, which has led to the intense processing of oak trees by the forestry industry. As a result, large amounts of forestry by-products (bark and leaves) are left in the woods, considered valueless. Thus, the aim of this study was to evaluate and compare the phytochemical profile and potential biological activities of Q. petreaea Matt. and Q. pubescens Willd. bark extracts. The extracts were obtained by microwave (MAE) and ultrasound-assisted extraction (UAE) with water (100%) and ethanol:water (70:30). These extracts were then characterized in terms of the total polyphenolic and tannin contents using the Folin–Ciocâlteu method. Their antioxidant properties were determined by observing the neutralizing effects of the extracts against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radicals. The antimicrobial effect was tested on Gram-positive and Gram-negative bacterial strains and three fungi from the Candida genus. Cellular counts were measured to determine the cytotoxic effects of the extracts on HEK 293T cell lines. Moreover, spectrophotometrical assays were performed to assess the inhibitory effects of the extracts against the enzymatic activity of α-glucosidase, tyrosinase, and acetylcholinesterase. The MAE resulted in higher yields of polyphenolic compounds and tannins compared to the UAE bark extracts. All of the experimental variants exhibited free-radical-neutralizing properties, especially Q. petraea extracts. Q. petraea extracts also had a more efficient antibacterial effect, especially against Gram-positive bacteria and K. pneumoniae. Antifungal activity was highlighted against C. krusei. Cell counts indicated a cytotoxic effect of the tested extracts against HEK 293T cells. The tested extracts inhibited the activity of α-glucosidase, tyrosinase, and acetylcholinesterase, indicating the potential use of these extracts as antidiabetic, neuroprotective, and skin-protecting agents. These findings highlight the untapped therapeutic potential of the bioactive compounds found in the bark of Q. petraea and Q. pubescens. [ABSTRACT FROM AUTHOR]

The northern red oak (Quercus rubra L.) is an ornamental oak species native to eastern America, being an invasive species in Europe, with increasing coverage. The aim of this work was to evaluate the biological potential of red oak bark extracts. Aqueous and ethanolic preparations were obtained by two extraction methods: ultrasonic-assisted extraction (UAE) and microwave assisted extraction (MAE). The total phenolic and tannin contents were measured using spectrophotometric methods. The antioxidant activity was evaluated by two complementary methods (DPPH and ABTS). Antimicrobial potential was tested against five bacteria and three Candida species, and the effect on biofilm formation and synergism with gentamicin was also evaluated. Finally, enzyme inhibitory properties were assessed for α-glucosidase, tyrosinase, and acetylcholinesterase. The results indicated a higher phenolic content for the extracts obtained through MAE, while UAE bark extracts were rich in tannins. All the extracts exhibited antioxidant, anti-glucosidase, and anti-tyrosinase activity, while the antibacterial potential was mostly observed for the MAE extracts, especially against S. aureus, C. parapsilopsis, and C. krusei; inhibition of biofilm formation was observed only for MRSA. These findings show that the red oak bark might be an important source of bioactive compounds with antioxidant and antimicrobial properties. [ABSTRACT FROM AUTHOR]

Recent studies highlight the great potential of the plants from the Quercus genus to comprise high contents of bioactive compounds with beneficial effects on human health. The aim of our work is to screen the potential biological effects of the bark of two oak species, namely Quercus petraea and Q. pubescens.The vegetal material was extracted using two different solvents (water and ethanol solution) and extraction methods, namely ultrasonic assisted extraction (UAE) and microwave assisted extraction (MAE). The total polyphenolic and tannin contents were quantified using the Folin-Ciocâlteu method. The antioxidant capacity of the extracts was tested using two complementary methods based on the 1,1-diphenyl-2-picrylhydrazyl -- DPPH and 2,2'-azino-bis(3- ethylbenzothiazoline)-6-sulfonic acid -- ABTS reagents. The antimicrobial activity was evaluated on five different bacterial strains (Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) and three fungi from the Candida genus (C. albicans, C. parapsilosis, C. krusei). Moreover, three enzymes were tested to evaluate the potential inhibitory effects of the extracts (α-glucosidase, tyrosinase and acetylcholinesterase). Higher total polyphenols and tannin yields were observed in the extracts obtained by MAE, compared to the UAE bark extracts. Also, the ethanolic solution was the better solvent for the extraction of bioactive compounds. Antioxidant activities were highlighted for all the tested extracts. A better antibacterial activity was observed against the Gram positive bacterial strains and Klebsiella pneumoniae, extracts from the bark of Quercus petraea being more efficient. The antifungal activity was highlighted against C. krusei. The tested extracts inhibited the activity of α-glucosidase, tyrosinase and acetylcholinesterase. These results highlight biological effects of the bioactive compounds found in the oak bark, that may be used in future pharmaceutical formulations, due to their beneficial effects on human health. [ABSTRACT FROM AUTHOR]