Characterisation of bioactive compounds obtained from forest trimmings by microwave assisted extraction (MAE) using Deep Eutectic Solvents (DES)

Today, forest cutting residues are seen as having an important potential to meet the raw material needs of many products. In addition to the positive effects of leaving them in nature, the most important drawback is that a great deal of potential remains idle, and the high amount of biomass they will form when they dry out increases the risk of fire. Although there are studies on the extractive components and characterization of annual shoots and branches of forest trees, with the recent development of new environmentally friendly, energy-, cost-, and time-effective solvents and extraction methods, the need to investigate how the composition of biomass will change qualitatively and quantitatively and the effects of different solvents on this change has emerged. In this study, characterization and antimicrobial activities of extracts and essential oils obtained from forest-cutting wastes consisting of needles, leaves, and shoots of larch (Pinus nigra), oak (Quercus robur), fir (Abies nordmanniana), and beech (Fagus orientalis) trees were carried out by the Microwave-Assisted Extraction Method (MAE) using Deep Eutectic Solvents (DES) and organic solvents. Volatile components were analyzed by GS-MS-SPME, and non-volatile components were analyzed by LC-MS/MS. The sugar and organic acid content of each extract were determined by HPLC analysis. The leaf surfaces of the trees used before and after extraction with each solvent were imaged by SEM (Scanning Electron Microscopy). The total phenolic, flavonoid, and anthocyanidin contents of the extracts were determined by methods. DPPH, ABTS, and CUPRAC analyses were performed to determine the antioxidant activities of the extracts and essential oils, and scavenging, trolox, and IC50 values were calculated. In addition, by disk diffusion method, the extracts and essential oils were determined to have antimicrobial activities against Staphylococcus aureus, Escherichia coli, Candida albicans, Pseudomonas aeruginosa, and Bacillus cereus strains. As a result of the extraction process, the yields of the extracts using deep eutectic solvents were in the range of 29,56-72,57%. In the leafy annual shoots of larch, oak, fir, and beech trees, 1R-α pinene was found in the volatile component analysis with the highest percentages of 14,19%, 14,42%, 17,76%, and 25,80%, respectively. Among the 23 components detected in the extracts by LC-MS/MS analysis, shikimic acid and catechin components gave the highest results. Ethanol+Kç gave the highest value with 263,203 µg/L for shikimic acid, and ethanol+M samples gave the highest result with 11,495 µg/L for catechin. The döç-3+K sample had the highest sugar content among the extracts, with 195,948 g/L of turanose and 82,393 g/L of maltose. In terms of total phenolic content, the extracts obtained from methanol and ethanol solvents had the highest content, with values in the range of 77,238–237,637 mg/L and 183,316–242,436 mg/L, respectively. Similarly, the highest results in terms of total flavonoid content were obtained from the extracts obtained from methanol and ethanol solvents, which gave values in the range of 68,072–192,517 mg/L and 153,628–222,114 mg/L, respectively. Acetone+M and methanol+M had the highest total anthocyanidin content, with 1,920 mg/L and 0,818 mg/L, respectively. According to IC50 values, acetone+K and ethanol+M gave values of 5,18 mg/L and 7,72 mg/L, respectively, in DPPH analysis; döç-1+K and purified water+G extracts, which gave results of 1,79 mg/L and 8,82 mg/L, respectively, in ABTS analysis, showed the highest antioxidant activity. In CUPRAC analysis, ethanol+K and methanol+M extracts showed the highest antioxidant activity, with the highest trolox result of 116,077 mg/L and 111,311 mg/L, respectively. ethanol+G extract showed the highest antibacterial activity among all samples, forming a 15 mm zone against B. cereus. Consequently, high yield extracts, obtained from deep eutectic solvents, were found to have a high sugar content due to the degradation of the main components of wood. Although extracts obtained from organic solvents showed lower yields than from deep eutectic solvents that they are thought to have a better ability to dissolve phenolic components in the plant due to their high polarity. The extracts rich in phenolic compounds were found to have high antioxidant, antibacterial, and antifungal activities. It is suggested that the extracts obtained from the leafy annual shoots of larch, oak, fir, and beech trees, widely used in the industrial production, can be used in pharmacology, the cosmetics industry, and as food supplements in terms of antioxidant, antibacterial, and antifungal activities. In this way, it is suggested that by utilizing industrial forest trimming residues, especially in the health sector, both an important factor that poses a great risk for fires can be eliminated by recycling forest felling residues and value-added products can be produced to meet the demand of society for the use of natural and organic-based products.