Extracts from the June collection of aerial parts of Helianthus salicifolius A. Dietr and Helianthus tuberosus L. were obtained using carbon dioxide supercritical fluid extraction with water as co-solvent. The antimicrobial effect in vitro of these extracts was then determined against reference species of bacteria, as well as against fungi (represented by Candida spp.). Both extracts were found to possess antimicrobial activity, with MIC = 0.62–5 mg mL⁻¹ for bacteria and MIC = 5–10 mg mL⁻¹ for yeasts, and both extracts demonstrated suitable bactericidal and fungicidal effect. The highest activity was observed against S. aureus ATCC 29213 (MIC = 0.62 mg mL⁻¹ for H. salicifolius extract; MIC = 2.5 mg mL⁻¹ for H. tuberosus extract) as confirmed by time–kill assay. Higher antioxidant activity was found for H. tuberosus extract (EC₅₀ = 0.332 mg mL⁻¹) as compared to that of H. salicifolius (EC₅₀ = 0.609 mg mL⁻¹). The total polyphenol content (TPC) expressed as gallic acid equivalents (GAE) was 13.75 ± 0.50 mg GAE g⁻¹ of H. salicifolius extract and 33.06 ± 0.80 mg GAE g⁻¹ of H. tuberosus extract. There was a relationship between the antioxidant potential of both extracts and TPC, but not between antistaphylococcal activity and TPC. The ATIR–FTIR spectra of both extracts showed similar main vibrations of the functional groups typical for phytoconstituents possessing bioactivity. The obtained data suggest potential application of these extracts as natural antioxidants and preparations with biocidal activity. Additionally, both extracts may be regarded as potential natural conservants in cosmetics, as well as natural preservatives in food.

In the bio-based economy concept, any biomass should not be used directly for energy purposes without considering the possibility of using it for bioproducts with higher added value. Extractable phytochemicals found in lignocellulosic biomass of perennial industrial crops (PIC) are used in the pharmaceutical, cosmetics, chemical, food and feed industries. Therefore, these compounds should be obtained first, and only the so-called PIC extraction biomass should be used, for example, for the production of bioenergy. An efficient low-energy and environmentally friendly method of extracting phytochemicals from the plant biomass is supercritical carbon dioxide (scCO₂) extraction. The aim of the study was to assess the thermophysical properties and chemical composition of 19 types of PIC biomass previously subjected to two types of scCO₂extraction compared to the biomass before extraction. The biomass after pure scCO₂and scCO₂/H₂O (1 wt%) extraction contained less ash (by 4.9 and 11.3%), carbon (by 3.1 and 7.8%), hydrogen (by 5.8 and 8.9%), nitrogen (by 4.5 and 6.8%), sulfur (by 3.8 and 3.8%), lignin (by 5.4 and 1.1%), hemicellulose (by 14.4%) and more chlorine (by 4.7 and 15.3%) compared to the biomass before extraction. In addition, the biomass after extraction with pure scCO₂contained more cellulose and was characterized by lower moisture content and higher heating value and lower heating value. However, the biomass after scCO₂/H₂O extraction contained more substances soluble in cold and hot water. Generally, the bark of four short-rotation coppice (SRC) species was characterized by a high content of nitrogen, sulfur, substances soluble in cold and hot water, other soluble substances and at the same time low cellulose content (26–28% d.m.). In turn, the wood of all SRC species was characterized by a high cellulose content (51–56% d.m.). However, all herbaceous crops and grasses contained more chlorine, hemicellulose and generally less lignin compared to the SRC biomass. To assess the practical suitability of the PIC biomass extraction for the production of bioenergy (solid, liquid or gaseous biofuels), further research is needed.