Optimization of Microwave Assisted Extraction Conditions to Improve Phenolic Content and In Vitro Antioxidant and Anti-Microbial Activity in Quercus cerris Bark Extracts

Abstract

The species of the Quercus genus, including Quercus cerris L., are widely used and their wood represents a valuable material utilized for various purposes. The intense industrial processing of wood results in a considerable amount of poorly-used natural by-products, such as bark, and a loss of potentially useful raw materials. Thus, the aim of our study was to evaluate the phytochemical characteristics and potential biological activities of Quercus cerris bark extracts obtained by optimizing the parameters of microwave assisted extraction (MAE). The optimum conditions for MAE were determined using a design of experiments (DoE) model, which set the experimental variables (irradiation time and microwave power) and their values. Aqueous and hydroalcoholic extractions were performed and the optimum parameters of extraction were determined for both solvents. The total polyphenolic and tannin contents were determined. The biological activities representative of antioxidant capacity were determined using two free radical scavenging methods, the DPPH and ABTS methods, and the antibacterial activity was assessed with the microdilution method. The results showed different optimal extraction conditions for aqueous (30 min at 850 W) and hydroalcoholic (18 min at 650 W) extracts. A higher yield of total polyphenols was observed in the hydroalcoholic bark extract (403.73 ± 7.35 mg gallic acid equivalents/g dried weight); however a lower level of tannins was registered in comparison to the aqueous extract. In addition, both extracts exerted high antioxidant activities, with the aqueous extracts having a stronger inhibitory effect against the DPPH radical. Moreover, the extracts exhibited antibacterial activity against the tested bacterial strains, especially against the Gram-positive strains and Klebsiella pneumoniae, with the hydroalcoholic extracts being more efficient overall. To conclude, the optimized MAE was an efficient method to extract phytochemical compounds with potential biological effects from Quercus cerris bark.

Antimicrobial Properties of Bacterial Cellulose Films Enriched with Bioactive Herbal Extracts Obtained by Microwave-Assisted Extraction

“…This could be because more liposoluble compounds were extracted over a high concentration of ethanol. In addition, the antibacterial activity of the extracts may be associated with their chemical composition and active compounds [ 41 , 42 , 43 ].…”

“…Additionally, the influence of the ethanolic concentration on the antimicrobial activity of all tested herbs against S. aureus reached statistical significance (b = 0.045; p = <0.0001), showing that an increase in concentration caused an increase in antimicrobial activity. This could be because the extraction rate of active compounds, not necessarily phenols, seems to increase when ethanol concentration elevates [ 51 ], and thus increases the antibacterial activity, which is directly related to the active compounds [ 41 , 42 , 43 ]. Additionally, an increase of microwave power during extraction was shown to significantly decrease the efficiency of the extracts against S. aureus (b = −0.001; p = 0.005).…”

“…Although many studies have evaluated the effect of these parameters on the phenolic content and antioxidant activity of ethanolic extracts [ 41 , 42 , 43 ], to the best of our knowledge, there are no previous studies that assessed the influence of microwave-assisted extraction parameters on the antimicrobial activity of herbal extracts against the tested microbial strains. Therefore, we assume that this is the first study that intends to assess the influence of microwave-extraction parameters over the antimicrobial activity of rosemary, oregano, parsley, and lovage ethanolic extracts.…”

Updating the status quo on the extraction of bioactive compounds in agro-products using a two-pot multivariate design. A comprehensive review

“…Applications of d -optimal design in food chemistry have been employed, such as extracting phenolics from Quercus cerris bark extracts, 119 Thymus comosus , 120 γ-oryzanol from Oryza sativa L. bran, 121 and carotenoid from orange peel. 116…”

Potential Use of Quercus dalechampii Ten. and Q. frainetto Ten. Barks Extracts as Antimicrobial, Enzyme Inhibitory, Antioxidant and Cytotoxic Agents

“…Q. dalechampii has brown bark with deep fissures ( Figure 1 a). Further, bark fragments were supposed to drying procedure (artificial drying for 24 h at 50 °C using a Nahita 631 Plus drying oven—Auxilab S.L., Beriáin, Spain) followed by milling of dried plant material (Pulverisette 15 cutting mill—Fritsch GmbH, Idar-Oberstein, Germany) [ 23 , 24 ].…”