The present study described the optimization of the extraction process with carbon dioxide in supercritical state for obtaining extractives, especially polyphenols from softwood bark, Norway spruce (Picea abies (L.) Karst.). Using a full 23 factorial design of experiments, the effect of varying the working parameters on the yield of extractives was studied for the following ranges: temperature 40–100 °C, pressure 1050–9000 psi (7.2–62 MPa), and concentration of EtOH/water co-solvent mixture 40–96.6%. In addition, total phenolics content and the antioxidant capacity of the spruce bark extract were determined. The optimum operating conditions for the yield of extractives were identified as 73 °C, 6465 psi (44.5 MPa), and 58% EtOH/water cosolvent concentration for a yield of 8.92%. The optimum conditions for achieving a total phenolics content of 13.89 mg gallic acid equivalent (GAE)/g dry extract were determined as: 45 °C, 1050 psi (7.2 MPa), and 96.6% EtOH/water mixture.

Extracts from spruce bark obtained using different deep eutectic solvents were screened for their total phenolic content (TPC) and antioxidant activities. Water containing choline chloride-based deep eutectic solvents (DESs) with lactic acid and 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol, with different molar ratios, were used as extractants. Basic characteristics of the DESs (density, viscosity, conductivity, and refractive index) were determined. All the DESs used behave as Newtonian liquids. The extractions were performed for 2 h at 60 °C under continuous stirring. TPC was determined spectrophotometrically, using the Folin-Ciocalteu reagent, and expressed as gallic acid equivalent (GAE). The antioxidant activity was determined spectrophotometrically by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The TPC varied from 233.6 to 596.2 mg GAE/100 g dry bark; radical scavenging activity (RSA) ranged between 81.4% and 95%. This study demonstrated that deep eutectic solvents are suitable solvents for extracting phenolic compounds from spruce bark.

Closed-system microwave-assisted extraction was applied to extract total phenolics from spruce (Picea abies) bark, using 96.6% ethanol as an extractant. The influence of particle size (0.3; 1.0; 2.5 mm), time (3 to 20 min), and temperature (60; 80; 100 °C) on polyphenol recovery was also studied. Higher extraction temperature and smaller particle size resulted in a higher yield of extracted polyphenols. However, the effect of extraction time on yield was more complicated. The effect of all three factors is tentatively explained.

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This article presents the results obtained in the extraction of birch bark with a green solvent. A low transition temperature mixture (LTTM) consisting of choline chloride (ChCl) and lactic acid in a molar ratio of 1:1 was used as the solvent. Extraction was performed at 60°C and 80°C. At both temperatures, the effect of extraction time on the yield of the extracted substances was monitored. The yields reached were compared with those obtained in studies using common solvents such as ethanol, methanol, d-limonene, ethyl acetate, and others. The extract was quantitatively analyzed by HPLC-UV to determine betulin and betulinic acid (0.491–1.788 mg/g dry bark and 0.106–0.316 mg/g dry bark, respectively). Total phenolic content was determined spectrometrically using Folin–Ciocalteu reagent and expressed as Gallic acid equivalents (GAE; 18.6–56.8 mg GAE/g dry bark). This study has shown that extraction with a green solvent composed of ChCl and lactic acid can be an effective method for extracting polyphenolic compounds from birch bark. The process for extracting triterpenes (betulin and betulinic acid) is less suitable compared to conventional methods using the mentioned organic extractants.

In recent years, significant progress has been achieved in developing natural drugs derived from medicinal plants. Multiple in-vitro screening studies reported that some naturally occurring compounds could possess inhibitory activity against various human viruses. The presented work describes significant biological activities of the main class of secondary metabolites such as phenolic compounds and terpenes located in industrially important tree species Norway spruce (Picea Abies) and Scots pine (Pinus Sylvestris). Phytochemicals show promising in vitro antiviral and cytotoxic activities, making them an attractive starting material for new development in various pharmaceutical products. They have the potential to effectively protect human health against cardiovascular diseases, diabetes mellitus, and as therapeutic agents against the SARS-CoV-2 virus.

In this study, the effect of extraction conditions on the total phenolic content of clove buds was investigated. Clove buds were extracted using a deep eutectic solvents like mixtures choline chloride: lactic acid in the 1:2 molar ratio. Additionally, the HPLC-DAD method was used to determine the main components of the clove extracts, including eugenol, eugenol acetate, and β-caryophyllene. The conditions used in the extraction with choline chloride: lactic acid (molar ratio 1:2) included extraction temperature (t = 40 – 80°C), water addition (5.6 – 40%), and extraction time (30 – 90 min). Determination of the phenolic compounds was done by the Folin-Ciocalteu method. The optimum operating conditions for the total phenolic content were identified at 77°C, 30 min, and a water addition of 40%. Based on the results, the highest amount of eugenol (307.26 ± 8,44 mg/g dry raw material) was determined in clove extracts which were extracted under condition of 60°C, 22.8%, and 30 min.

The antioxidant potential of extracts from spruce bark was studied after Soxhlet extraction with ethanol and n-hexane. Ethanol spruce bark extracts were pre-extracted with a mixture of ethanol and n-hexane in a ratio of 1:5. Residues of the extracts and pre-extracts were added to lard (200 mg/kg) to examine its influence on oxidation stability of lard. The composition of the bark extractives was analyzed by GC/MS. The highest antioxidant activity was observed in the original ethanol extracts (15.0 mmol/mg), which had greater antioxidant activity than alpha-tocopherol (13.9 mmol/mg). The n-hexane extract from the spruce bark had 70% less antioxidant activity than the ethanol extract. The high antioxidant activity of the ethanol extract was due to the presence of resin acids (35%) and stilbenes (12%). These antioxidant-active substances increased the oxidation stability of the lard by 5 h, while the n-hexane extract increased the oxidation stability by only 0.5 h. The spruce bark was found to be an alternative feedstock of compounds with potential for use in foodstuffs as antioxidant.