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1.
Exploring antioxidative properties of xanthohumol and isoxanthohumol : an integrated experimental and computational approach with isoxanthohumol pKa determination
Jelena Tošović, Zala Kolenc, Gregor Hostnik, Urban Bren, 2025, original scientific article

Abstract: This study explores the antioxidative activities of xanthohumol (XN) and isoxanthohumol (IXN), prenylated flavonoids from Humulus lupulus (family Cannabaceae), utilizing the oxygen radical absorption capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays along with computational Density Functional Theory methods. Experimentally, XN demonstrated significantly higher antioxidative capacities than IXN. Moreover, we determined IXN pKa values using the UV/Vis spectrophotometric method for the first time, facilitating its accurate computational modeling under physiological conditions. Through a thermodynamic approach, XN was found to efficiently scavenge HOO• and CH3O• radicals via Hydrogen Atom Transfer (HAT) and Radical Adduct Formation (RAF) mechanisms, while CH3OO• scavenging was feasible only through the HAT pathway. IXN exhibited its best antioxidative activity against CH3O• via both HAT and RAF mechanisms and could also scavenge HOO• through RAF. Both Single Electron Transfer (SET) and Sequential Proton Loss-Electron Transfer (SPLET) mechanisms were thermodynamically unfavorable for all radicals and both compounds.
Keywords: antioxidative activity, bio-active membranes, xanthohumol, isoxanthohumol, ORAC and FRAP assays, pKa determination, density functional theory, DFT
Published in DKUM: 31.01.2025; Views: 0; Downloads: 0
.pdf Full text (2,80 MB)

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Antimicrobial properties of different hop (Humulus lupulus) genotypes
Zala Kolenc, Tomaž Langerholc, Gregor Hostnik, Miha Ocvirk, Sara Štumpf, Maša Pintarič, Iztok Jože Košir, Andreja Čerenak, Alenka Garmut, Urban Bren, 2023, original scientific article

Abstract: The antimicrobial activity of hop extracts obtained from different hop genotypes were investigated against Staphylococcus aureus and Lactobacillus acidophilus. In this study the pure xanthohumol, purified β-acids rich fraction, as well as α-acids with β-acids rich fraction were used to test antimicrobial activity against Staphylococcus aureus and Lactobacillus acidophilus; whereby, the antimicrobial activity of different hop extracts against Lactobacillus acidophilus was studied for the first time. Microbial susceptibility to purified hydroacetonic extracts from different hop varieties was investigated by the broth microdilution assay to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The hop hydroacetonic extracts were more effective against Staphylococcus aureus than against Lactobacillus acidophilus. Strong inverse correlations of MIC and MBC values were obtained with xanthohumol, cohumulone, n+adhumulone, colupulone and n+adlupulone contents, suggesting that the identified chemical hop compounds are directly responsible for antimicrobial effects. Moreover, the effect of the growth medium strength on the MIC values of hop extracts against Staphylococcus aureus was systematically investigated for the first time. The current study also reveals the effect of different hop extracts on Staphylococcus aureus, which responds to their presence by lag phase extension and generation time prolongation.
Keywords: hop extract, xanthohumol, Staphylococcus aureus, Lactobacillus acidophilus, minimum inhibitory concentration, minimum bactericidal concentration
Published in DKUM: 09.05.2024; Views: 203; Downloads: 18
.pdf Full text (2,03 MB)
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4.
Extraction and separation of active compounds by supercritical fluids extraction and preparative supercritical chromatography
Alejandro Bartolome Ortega, 2017, doctoral dissertation

Abstract: This doctoral dissertation is focused on the benefits of supercritical fluids technology in several industry processes. Although, supercritical CO2 is currently the most employed supercritical fluid at laboratory scale, its presence in the industry field is still limited, due to the necessity of high investment costs. Despite that fact, operations with supercritical CO2 are cheap, environmentally friendly and simple, which make it an excellent alternative to organic compounds. Extraction and separation of highly pure active compounds, such as xanthohumol or beta-sitosterol, are demanded for pharmaceutical or food industries, which create an excellent opportunity for supercritical CO2 operations, since they are solvent free. This manuscript is divided into three different parts. In the first part, conventional extraction processes and supercritical fluid process are theoretically compared and supercritical fluid extraction from saw palmetto berries is presented. In the second part, conventional chromatographic techniques and supercritical fluid chromatography are theoretically compared and separation of xanthohumol from hop extracts by supercritical fluid chromatography is presented. In the last part, different encapsulation and emulsification processes are listed and defined. These processes are very important for food and pharmaceutical companies, since several active compounds are not water soluble which create the necessity of different formulations in order to be solved in an appropriate media. Regarding the experimental part, extractions from saw palmetto berries were performed at various pressures and temperatures, which were higher than the ones that were applied in previous studies, in order to estimate and calculate different parameters (solubility, extraction kinetic curves, composition,…), and to compare different studies. Separation of xanthohumol was carried out in a homemade supercritical chromatography, which manageable variables were temperature, pressure, mass flow-rate, modifier, and stationary phase. The results were compared with those ones which were obtained using conventional techniques, in order to prove the suitability and the improvement of this technique against others tecniques.
Keywords: supercritical CO2, supercritical fluid extraction, supercritical fluid chromatography, xanthohumol, saw palmetto berries, Beta-Sitosterol, encapsulation
Published in DKUM: 13.07.2017; Views: 2243; Downloads: 251
.pdf Full text (3,20 MB)

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