| Abstract [eng] |
Hops (Humulus lupulus L.) are valued in the brewing industry for providing bitterness, aroma and taste to beers and in pharmacognosy for their antioxidant, antimicrobial, sedative and estrogenic effects. Hop extracts obtained through sustainable green processes contain valuable bioactives such as bitter acids, essential oils and polyphenols. Emerging novel applications of hop extracts are fuelled by the research on the ever-widening range of beneficial health effects of hop phytochemicals. This work aimed to develop effective supercritical carbon dioxide extraction (SFE-CO2) and pressurized liquid extraction with ethanol (PLE-EtOH) for the production of non-polar and polar extracts from dual-purpose Ella hops with high yield, strong antioxidant potential and high content of selected phytochemicals. After evaluation of commercial one-stage SFE-CO2 process at 10-15 MPa and 40°C of ground Ella hop pellets, response surface methodology (RSM) with central composite design (CCD) was applied to optimize the SFE-CO2 process at 25-45 MPa for high yield and in vitro oxygen radical absorbance capacity (TEACORAC assay). Through optimized SFE-CO2 (37 MPa, 43 °C, 80 min) conditions ~3-fold higher extraction yield, antioxidant and bitter acid recovery was achieved under significantly shorter extraction time compared to one-stage SFE-CO2 at 10-15 MPa and 40 ℃. The spectrophotometrical analysis of carotenoids and chlorophylls showed a negligible amount (<0.04%). The major volatiles identified through SPME-GC×GC-TOF-MS analysis, β-pinene, β-myrcene, β-humulene, α-humulene, α-selinene and methyl-4-decanoate attributed fruity, herbal, spicy and woody odour to the extracts. The impact of SFE-CO2 parameters on the bitter acid content was evaluated and optimized by RSM-CCD for maximum recovery. The optimal conditions (36 MPa, 40 °C, 90 min) produced a similar yield and higher total bitter acid content as the recovery of α-acids increased compared to the previous SFE-CO2 extract (37 MPa, 43 °C, 80 min). The antimicrobial effect of the SFE-CO2 extract (36 MPa, 40 °C, 90 min) was determined through agar well diffusion assays and confirmed against a strain of S. aureus and E. coli. The effect of the extract was also tested on the viability of skin cancer, healthy keratinocyte and fibroblast cells. Under the biorefinery concept, the residue of bitter acid optimized SFE-CO2 (HR) was further utilized for the extraction of polar compounds. PLE-EtOH process was optimized by RSM-CCD for high yield, antioxidant activity (measured by TPC and ORAC assays) and recovery of xanthohumol, a bioactive prenylflavonoid (analysed by HPLC-DAD). Optimal conditions were separated, maximized yield coupled with strong antioxidant potential (85 °C, 18 min), and maximized xanthohumol content (40 °C, 15 min). The PLE-EtOH extracts proved to have antimicrobial effects against a S. aureus strain in an agar well diffusion assay. |
