► 4-Vinyl derivatives were prepared by thermal decarboxylation of hydroxycinnamic acids. ► Their antioxidant properties were determined under various conditions for the first time. ► Decarboxylation ...lowered reducing and radical-scavenging capacities of phenolic acids. ► In emulsion derivatives were better antioxidants than phenolic acids. ► Antioxidant activity of compounds in emulsion is mostly defined by their partition.
The compounds 4-vinylphenol (4-VP), 4-vinylguaiacol (4-VG), 4-vinylsyringol (4-VS) and 4-vinylcatechol (4-VC) were prepared by thermal decarboxylation of the corresponding hydroxycinnamic acids p-coumaric, ferulic, sinapic and caffeic acid, respectively. For confirmation of the synthesised products LC–MS followed by NMR analysis was used. To evaluate their antioxidant potential, their reducing power and efficiency in scavenging the alkylperoxyl radical generated in an emulsion system, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and the superoxide anion radical (O2-) were determined. All tested 4-vinyl derivatives revealed weaker antioxidant activity in a homogeneous polar medium than the corresponding phenolic acids. In the emulsion system the activity for 4-vinyl derivatives was higher than was the activity of their corresponding phenolic acids, with 4-VG as the most active among the tested phenolic compounds.
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 at temperatures from 293.15 to 323.15 K. The dependence of these dielectric parameters on basic oil quality indices was investigated. Adding oleic acids to sunflower oil resulted in lower dielectric constants and conductivities and higher quality factors. 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, whereas conductivities followed the Arrhenius law.
To increase the stability of bioactive compounds and to protect them from adverse environmental conditions, they can be encapsulated in lipids and/or polymeric matrices. Here, pantothenic acid was ...encapsulated in liposomes and in different hydrogel microcapsules that consisted of alginate or alginate–pectin mixtures. With liposomes, an encapsulation efficiency of 0.75 ± 0.02 was achieved, and for alginate microparticles, 0.60 ± 0.02. The release of pantothenic acid from liposomes and from the different alginate–pectin microparticles loaded with liposomes followed first-order kinetics. For alginate microparticles and alginate microparticles loaded with liposomes, pantothenic acid release followed Higuchi kinetics, which suggests that this pantothenic acid release was mainly driven by a diffusion-controlled mechanism. To the best of our knowledge, this is the first report of the encapsulation of pantothenic acid.
•Pantothenic acid was encapsulated in liposomes and different hydrogel microcapsules.•Release from the liposomes followed first-order kinetics.•Release from alginate microparticles was driven by a diffusion-controlled mechanism.
The complex admittance and dielectric spectra of whipping creams were determined in the frequency range of 200 Hz to 2 MHz, and dielectric properties also of 0.2 GHz to 8.5 GHz at 298.15 K. The ...admittance spectra were fitted with appropriate equivalent circuits, subtracting dielectric constant and direct current conductivity. The electrical and dielectric properties are discussed in terms of the macro-component content of whipping cream (i.e., water, lipid, protein, carbohydrate).
•The dielectric dispersion ε′ of whipping creams decreased with increasing frequency.•The dielectric loss ε" of whipping creams had the minimum at ~1 GHz.•At 10 kHz < f < 2 MHz the electrical conductivity was independent of frequency.•The protein and carbohydrate impacted on ε′ and ε", as did the water and butterfat.
The dielectric properties of six refined edible oils with different fatty-acid compositions were determined for oils incubated at 180 °C up to 40 h. The oil degradation was evaluated by the ...dielectric dispersion and dielectric loss in the frequency range from 40 Hz to 2 MHz at 25 °C, refractive index, density, saponification number, and specific absorption coefficient at 232 and 268 nm. The dependence of the dielectric properties on frequency has been evaluated with Corach, Cole–Cole, and the universal power law models, giving the novel strategies for the interpretation of the dielectric spectra of thermally treated oils. The derived parameters—the dielectric constant, the electrical conductivity, the relaxation time τ and the exponents α, p, and n—are discussed with respect to the increased oxidation evidenced by specific absorption coefficients and polar products, as measured by the dielectric constant of the thermally treated oils. The specific refraction, specific polarization, orientation polarization, and dipole moment were determined using Lorenz–Lorentz, Debye and Onsager relationship. All above parameters obtained increased during the thermal treatment, except specific refraction, the electrical conductivity and the relaxation time. The dielectric constant-macroscopic parameter was compared with microscopic parameter polarization and dipole moment; the linear dependence was found to be R 2 = 0.971 .
Dielectric spectroscopy at low frequencies was applied to analyze vegetable oils, in particular roasted pumpkin seed oils (RPO). Large differences were observed for electrical conductivity not ...previously applied as a tool in the analysis of crude vegetable oils. RPO have two orders of magnitude higher conductivity than refined sunflower oils and extra virgin olive oils. Differences in dielectric constant were small and influenced by fatty acid composition and presence of minor components. The conductivity of pumpkin seed oils is highly correlated to phospholipid and metal contents. Phospholipids, magnesium, potassium and sodium are present at mmol/kg concentrations as determined by ICP-MS. We have shown that measurement of electrical conductivity can be used as a cost efficient method to detect adulteration of RPO with refined oils, even for those with similar fatty acid composition. Low background conductivity of triacylglycerols allows that even trace amounts of metals and phospholipids are detected in vegetable oils.
•Roasted pumpkin seed oils (RPO) have high electrical conductivity (κ).•κ of vegetable oils is highly correlated to metal ions and phospholipids.•Minerals and phospholipids in RPO are present at mmol/kg concentrations.•Measurement of κ can be used to detect adulteration of pumpkin seed oils.
The rate of reaction of phenolic antioxidants with DPPH depends on solvent composition. The rate constants can differ by more than two orders of magnitude for the same phenolic compound. Reactions ...are faster in alcohols than in ethyl acetate that is used routinely for the analysis of antioxidant potential (AOP) of nonpolar samples such as vegetable oils. Incorporation of an acid base pair into the assay solvent buffers the system against acid impurities such as free fatty acids and CO2 from the air. This is shown to increase the rate of oxidation and number of electrons of phenolic compounds exchanged with DPPH. Typically, DPPH assays are performed for predetermined time intervals at which phenolic compounds are not fully oxidized and therefore higher reaction rates result in higher values of AOP. More than twofold AOP was obtained for oleuropein, sesamol, sinapic acid, caffeic acid and protocatechuic acid in buffered alcohols than in ethyl acetate. The AOP of sesame, pumpkin seed and extra virgin olive oil is accordingly higher when determined in buffered alcohols. DPPH assays in ethyl acetate result in underestimation of AOP of unrefined vegetable oils.
•Antioxidant potential of unrefined oils is underestimated when analyzed in nonpolar solvent.•Antioxidants react with DPPH more than 100-fold faster in alcohols than in ethyl acetate.•Incorporation of a buffer into the solvent further increases the reactivity of antioxidants.•Antioxidant potential of unrefined oils is more correctly determined in buffered alcohols.
The electrical conductivities of aqueous solutions of quinic acid and its sodium salt were measured from 293.15 to 328.15 K in steps of 5 K. The molar conductivities of the sodium salt were treated ...by the Lee–Wheaton equation, in the form of Pethybridge and Taba, and the Kohlrausch equations. The limiting molar conductivities of the quinate anion were estimated, as well as the corresponding ionic association constants and standard thermodynamic functions of the ionic association reaction. The hydrodynamic radius of the quinate anion was calculated from the Walden rule and compared with the van der Waals radius. The dissociation constant of quinic acid was evaluated from the known value of the limiting molar conductivity of quinic acid using the conductivity equation of Pethybridge and Taba. The standard thermodynamic functions of the dissociation process, i.e., the Gibbs energy, enthalpy, entropy and heat capacity, were obtained using the non-empirical procedure given by Clarke and Glew. The standard thermodynamic functions of dissociation of quinic acid are discussed in terms of solute–solvent interactions and stabilization of the quinate anion due to hydrogen bonding of the α-hydroxyl group to the carboxyl group.
The apparent molar volume of quinic acid and its sodium salt were determined from the density data of aqueous solutions up to molality of 0.4 mol kg
−1
and in the temperature range from 293.15 to ...328.15 K. The apparent molar volume of sodium quinate comprises the ionic and the associated ion-pair contributions. From the apparent molar volumes of quinic acid and the quinate ion, the molecular contributions to that of quinic acid are derived. At 298.15 K, the limiting apparent molar volume of quinic acid is 119.8 ± 0.5 cm
3
mol
−1
, and that of the quinic ion is 111.6 ± 0.3 cm
3
mol
−1
. Similarly, at 298.15 K, the limiting apparent molar expansibility of sodium quinate is 0.198 ± 0.003 cm
3
mol
−1
K
−1
, and that of quinic acid is 0.142 ± 0.003 cm
3
mol
−1
K
−1
. From these limiting ionic and molecular apparent molar volumes, the limiting volume change caused by ionization of quinic acid was calculated as −8.2 cm
3
mol
−1
at 298.15 K. The coefficients of thermal expansion of these solutions were calculated from the density data, and from these the apparent molar expansibilities of quinic acid and its sodium salt were derived.
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