The leaves of the hop plant (Humulus lupulus L.) are an agricultural by-product that is not exploited. Like hop cones, hop leaves could also be used as a source of phenolic compounds. This study compared two hop cultivars from four different hop-growing regions (Žalec, Slovenia; Leutschach (Kranach), Austria; Hüll, Germany; Žatec, Czech Republic): cv. ‘Aurora’ and cv. ‘Hallertauer Magnum’. Leaves and cones of these two cultivars were collected and their total phenolics and the antioxidative and antimicrobial activities of their ethanol extracts were determined. Samples were collected three years in succession (2008-2010). The leaves had 3-fold to 30-fold less total phenolics than the cones, they were less efective antioxidants y (?5-fold less). Their IC50 with DPPH radicals was much higher, than the cones’ extracts regardless of the year and of the growing location. The best antioxidant was the extract from the Aurora leaves collected in the Czech Republic in 2010. Concerning antimicrobial activity, it was extraordinary for all hop cones extracts against gram positive Staphylococcus aureus (minimal inhibitory concentrations, MICs ( 0.003 mg/mL), but with a similar, moderate antimicrobial activity (MICs)0.16 mg/mL) for hop cones and leaves extracts against gram negative Escherichia coli O157:H7. The results of a profile HPLC analyses showed a big difference between the leaves and cones for an unidentified peak with tr =35.1 min. The cones had no peak with such retention time. Our conclusion is that hop leaves from both of the cultivars investigated here can be used as antioxidants, but not as antimicrobials against the microorganisms tested.
COBISS.SI-ID: 4453496
For vegetable oils with extremely different structure, oxidized, saturated and hydrolyzed, various electrical parameters, dielectric constant, dielectric loss factor and electrical conductivity and theirs’ temperature dependence were determined. Thus the frame of values characteristic for electrical properties for vegetable oils was evaluated. Model vegetable oil mixtures with significantly different basic oil quality indices (free fatty acid, iodine and Totox values) were prepared by adding oleic acids, synthetic saturated triglycerides, or oxidized safflower oil (Carthamus tinctorius) to the oleic type of sunflower oil. Dielectric constants, dielectric loss factors, quality factors, and electrical conductivities of model lipids were determined at frequencies from 50 Hz to 2 MHz and temperatures from 293.15 to 323.15 K. Dependence of these dielectric parameters on basic oil quality indices was investigated. Adding oleic acids to sunflower oil resulted in a lower dielectric constant and conductivities and higher quality factor. Reduced iodine values resulted in increased dielectric constants and quality factors, and decreased conductivities. Higher Totox values resulted in higher dielectric constants and conductivities at high frequencies, and lower quality factors. Dielectric constants decreased linearly with temperature, while conductivities followed Arrhenius’ law.
COBISS.SI-ID: 4329080
Solvent composition has a large influence on measured antioxidant potential (AOP) of model polyphenols and red wines with DPPH. We have shown that incorporation of aqueous buffer in the assay medium results in higher reactivity and more complete oxidation of catechin and caftaric acid, that are among major polyphenolic constituents of wines. Consequently AOPs of red wines determined in buffered methanol are 1.5- to 1.6-fold of values determined in pure methanol that is usually the solvent of choice. Parameters of DPPH assay should be standardized as minor differences in experimental procedures can account for large variations in determined AOP with DPPH for same samples.
COBISS.SI-ID: 4186488
This mini review focuses on advances in biophysical techniques to study polyphenol interactions with proteins. Polyphenols have many beneficial pharmacological properties, as a result of which they have been the subject of intensive studies. The most conventional techniques described here can be divided into three groups: (i) methods used for screening (in-situ methods); (ii) methods used to gain insight into the mechanisms of polyphenol–protein interactions; and (iii) methods used to study protein aggregation and precipitation. All of these methods used to study polyphenol–protein interactions are based on modifications to the physicochemical properties of the polyphenols or proteins after binding/ complex formation in solution. To date, numerous review articles have been published in the field of polyphenols. This review will give a brif insight in computational metods and biosensors and cell-based methods, spectroscopic methods including fluorescence emission, UV-vis adsorption, circular dichroism, Fourier transform infrared and mass spectrometry, nuclear magnetic resonance, X-ray diffraction, and light scattering techniqes including small-angle X-ray scattering and small-angle neutron scattering), and calorimetric techniques (isothermal titration calorimetry and differentiall scanning calorimetry), microscopy, the techniques which have been successfully used for polyphenol-protein interactions. At the end the new methods based on single molecule detection with high potential to study polyphenol-protein interactions will be presented. The advantages and disadvantages of each technique will be discussed as well as the thermodynamic, kinetic or structural parameters, which can be obtained. The other relevant biophysical experimental techniques that have proven to be valuable, such electrochemical methods, hydrodynamic techniques and chromatographic techniques are described here.
COBISS.SI-ID: 4537208
The influence of deodorization parameters (temperature, steam flow, time) on the phenolic content and radical scavenging effectiveness (RSE) of methanolic extracts of camelina oil was investigated and analysed by response-surface methodology (RSM). The phenolic content can be considered to be a linear function of all three parameters. A positive linear relationship between the content of phenolic compounds in deodorized oils and RSE was observed. Deodorization at 210 °C with a steam flow of 2.67 mL/h for 90 min resulted in the best preservation of phenolics, amounting to 29.9 mg/kg. The lowest reduction from RSE of 12.4 µM Trolox equivalents (TE)/g oil for the crude oil was observed for oil treated at 195 °C and 18 mL/h for 60 min with RSE of 10.1 µM TE/g oil. The lack of correlation between RSE or total phenolic content with oxidative stability of the deodorized oils suggests that antioxidants in scavenging radicals react by different mechanisms, depending on radical type and reaction medium.
COBISS.SI-ID: 4278136
The coating on the oral surface plays a significant role in mouthfeel perception, which is an important attribute governing perception of reduced-fat or low-fat food products. The aim of this work was to develop efficient methods to quantify the coating of the lipids covering the oral surface after ingestion of fatty foods. Three different approaches were assessed to investigate the in-mouth behavior of fluid foods in a subject. A first approach determined the mass of lipids retained in the oral cavity by rinsing it out. A second approach evaluated the thickness of the lipid coating on the tongue by fluorescence measurement using a dye incorporated in oil. Finally, a third approach measured local lipid thickness by adsorption of the lipids on a filter paper. All applied methods showed results in the same range. The thickness of the lipid coating was on average between 5 and 32 µm. The total lipid recoveries obtained by controlled rinses from the oral cavity were approximately 96 and 50% for single filter paper. A fast, simple, and quantitative method was developed to measure the thickness of the lipid coating on an oral surface after ingestion of fatty foods. This work presents the potential of the method to investigate in-mouth distribution and residues of lipids and establishes new avenues to study in-mouth behavior of food components and its influence on the sensory perception.
COBISS.SI-ID: 3414136
We programmed an interactive application as a tool in aid of educating all personnel involved with delivering electroporation-based treatments in applications of electroporation. In example, in electrochemotherapy, as well as in other applications of electroporation, good coverage of the target tissue area with a sufficiently strong electric field is of paramount importance. In addition to plate electrodes, needle electrodes are often used in order to apply electric pulses and are used instead of parallel plate electrodes. The electric field generated by needle electrodes in tissue is highly inhomogeneous. The application described in this paper was thus programmed so as to allow the student to move and re-position from one up to six pairs of needle electrodes within an area depicting heterogeneous tissue, where the objective is to achieve the highest coverage of target tissue area with an electric field of sufficient strength while trying to preserve as much of tissue as possible from exposure to excessively high fields. The on-line version of the application is a part of the practical laboratory exercise within the scope of international School and post-graduate course EBTT (Electroporation-Based Technologies and Treatments) that is annually organised at the University of Ljubljana, Faculty of Electrical Engineering. The application uses an extremely fast algorithm based on an analytical solution for field strength that was developed specifically for this application.
COBISS.SI-ID: 9515092
A new folding intermediate of Oxytricha nova telomeric Oxy-1.5 G-quadruplex was characterized in aqueous solution using NMR spectroscopy, native gel electrophoresis, thermal differential spectra (TDS), CD spectroscopy, and differential scanning calorimetry (DSC). This study provides evidence that G-rich DNA sequences in absence of metal cations can self-assemble into specific pre-organized DNA structures that are predisposed to fold into G-quadruplex when interacting with cations such as potassium ions. The knowledge used to describe kinetically driven structure transitions can be also applied to food systems. Because many food processing methods involve thermal treatment (heating, cooling, freezing) of the materials, processing parameters such as cooling rate, crystallization temperature, agitation rate and the use of additives can influence physicochemical and crystallization properties during storage and in the final texture.
COBISS.SI-ID: 1701423
We have shown that unfolding of model telomeric human DNA (Tel22) in the presence of K+ ions may be described as a monomolecular equilibrium three-state process that involves thermodynamically distinguishable folded (F), intermediate (I), and unfolded (U) state. Our results represent the first experimental support of the suggested unfolding/folding mechanism of Tel22 transitions can because observed changes in thermodynamic parameters can be reasonably explained only if the intermediate state I is considered to be a triplex structural conformation. Approaches and techniques used to study interactions between salt and biological macromolecules could be applied to study interactions between starch, proteins, lipids and different additives in the presence of water in food products. Since these components form complex matrix ,understanding their interactions could help improve functionality and quality of food products.
COBISS.SI-ID: 36015365
Resveratrol-loaded alginate submicron particles were prepared by emulsification followed by external gelation. Scanning electron microscopy analysis of the air-dried and freeze-dried submicron particles demonstrated their spherical shape, from 100 nm to 600 nm in size. The encapsulation efficiency and loading for resveratrol were 24.5% (±1.6%) and 0.3% (±0.05%), respectively. The interactions between the encapsulated resveratrol and alginate were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. The release from the alginate submicron particles was successfully described by the linear superimposition model, which allowed concluding that resveratrol transport is governed by Fick’s diffusion. The alginate submicron particles were prepared from materials that are considered as generally recognized as safe, and thus have good potential for use as a resveratrol delivery system in food products.
COBISS.SI-ID: 4530296