Organic Radical Concentration Research Articles

Development and Correlation between the Organic Radical Concentration in Different Malt Types and Oxidative Beer Stability

An optimized version of the patented electron spin resonance spectroscopy method, using a novel internal standard (52Cr: MgO), was used to monitor the development of organic radicals during the malting process and the radical content in different commercial specialty malts. The temperature during the withering and kilning steps in malt production had a direct influence on the generation of stable organic radicals in the finished malt, whereby higher temperatures resulted in greater radical concentrations. The majority of organic radicals in pilsner malt were bound in the husk and, therefore, did not significantly transfer into the wort and subsequent beer. In roasted malts, the organic radicals were distributed more uniformly throughout the kernel. Furthermore, depending on the organic radical content and Maillard reaction products present in the endosperm of crystal and roasted malts, more oxidation reactions took place during the mashing, and there was higher radical formation during the wort boiling process. Consequently, the endogenous antioxidant potential value and sulfur dioxide content in the final beer were reduced. These results indicate that there is a direct link between organic radicals in the endosperm generated by the kilning temperature during the malting process and color as an indicator of Maillard reaction products and the oxidative stability of the resultant beer.

Nature and Abundance of Organic Radicals in Natural Organic Matter: Effect of pH and Irradiation

Dissolved natural organic matter (NOM) plays an essential role in freshwater geochemical and biochemical processes. A major property, its redox behavior, can be attributed to the chinone building blocks, which can form stable radicals. However, electron paramagnetic resonance (EPR) data indicating free radicals on solid NOM are sparse. Here we present EPR spectra of 23 NOM from European surface waters isolated by reverse osmosis. The organic radical concentrations of NOM ranged from 5 x 10(15) to 1.84 x 10(17) spins g(-1), and g values ranged from 2.0031 to 2.0045. Number and type of organic radicals in solid NOM are significantly influenced by the pH of raw water. EPR experiments indicate the presence of semiquinone-type radicals in coexistence with carbon-centered "aromatic" radicals, with the semiquinone-type radicals dominating at alkaline pH. Basically these processes are reversible. Organic radical concentrations in NOM adjusted to pH 6.5 before freeze-drying correlate with iron and aluminum contents. UV- and VIS-irradiation of solid NOM can lead to more than a 10-fold increase of the concentration of organic radicals. These radicals were long-lived and had the same g value as the original radical. Similar effects were not observed with isolated humic and fulvic acids, demonstrating the limited reflection of environmental properties of organic carbon by the classical isolation procedure.

Oxidation of Dihydroxybenzenes in Aerated Aqueous Suspensions of Birnessite

AbstractThe oxidation of 1,2- and 1,4-dihydroxybenzenes (1,2-DHB and 1,4-DHB) by unbuffered aerated suspensions of synthetic bimessite was studied by continuously monitoring the H+, Mn2+, dissolved O2, and organic radical concentration of the aqueous phase during the reaction. The reaction rapidly generated a very high pH, attributed to oxide dissolution, and the alkaline conditions prevented Mn2+ release into solution over the entire reaction period. Semiquinone radical anions accumulated early in the reaction and then diminished. A secondary radical product appeared in solution during the reaction of the oxide with 1,2-DHB, and was tentatively identified as an hydroxylated semiquinone. The oxide/DHB ratio controlled the maximum concentration and persistence of these radicals in solution as well as the degree to which O2 was consumed as an electron donor. In general, low oxide/DHB ratios promoted O2 uptake by the system, consistent with the subordinate role of O2 as a competing electron acceptor in the presence of excess Mn oxide. Soluble phosphate suppressed O2 consumption, but the mechanism by which it interacted with the reaction system was not determined.

High temperature, high pressure ESR study of molybdenum-containing catalysts

The reduction of molybdenum in molybdenum trioxide over various supports was studied using high-temperature, high-pressure ESR techniques. The support materials have a great influence on the reduction behaviour of the catalysts at high temperatures under a high pressure of hydrogen. The ease of reduction of molybdenum in the order MoO3/SnO2 > MoO3/ZrO2 > MoO3/TiO2 > MoO3/Al2O3 > MoO3/SiO2 > MoO3/MgO.To clarify the interaction between catalysts and reactants, the molybdenum-containing catalyst-9-methylanthracene system was monitored. An electron-transfer reaction from 9-methylanthracene to catalysts occurred and both organic radicals and Mo(V) species were observed at the same time. It was found that the behaviours of organic radicals and Mo(V) species depend on the support materials, i.e. the organic radical concentration increases with increasing Mo(V) concentration for the MoO3-Al2O3-9-methylanthracene system in the temperature range 381 – 558 K. On the other hand, the organic radical concentration is inversely proportional to Mo(V) concentration for the MoO3-ZrO2-9-methylanthracene system in the range 399 – 493 K.