S. M. Glidewell

Free radical reactions involving coffee

Abstract Instant coffee solutions were shown by electron paramagnetic resonance (EPR) spectroscopy to act as proxidants by enhancing the production of ascorbyl radicals from ascorbic acid. The coffee solutions were also shown to act as scavengers of superoxide radicals in competition with a spin trap. The radical scavenging capabilities of several components of coffee were similarly investigated. There was little difference between the radical scavenging abilities of regular and decaffeinated coffee solutions.

Seed mass variation potentially masks a single critical water content in recalcitrant seeds

For recalcitrant seeds, mortality curves of germination versus water content typically imply a wide range of desiccation sensitivities within a seed population. However, seed to seed differences in water content, during desiccation, may confound our interpretation of these mortality plots. Here, we illustrate this problem for two batches of Vitellaria paradoxa ( Sapotaceae ) seeds collected in 1996 and 2002. Whole seeds were desiccated to various target water contents (TWCs) using silica gel. During desiccation, smaller seeds in the population dried most rapidly. Consequently, there was a significant linear relationship between whole-seed water content and seed mass during the drying process. In addition, following desiccation to low TWCs, only the largest seeds in the population retained viability. Taken together, this suggests that the larger seeds survived, not as a consequence of great relative desiccation tolerance, but as a result of taking longer to desiccate. Subsequently, the critical water content (CWC) for viability loss was calculated, based on the assumptions that in the seed population whole-seed water content during desiccation was normally distributed and the smallest, and hence driest, seeds were killed first. Using this approach, the driest seeds in the population that were killed, at each TWC, were always below a single CWC ( c . 20% and 26% in 1996 and 2002, respectively). In subsequent experiments the effect of seed size variation on the response to desiccation was confirmed by conducting desiccation screens on seeds sorted into two discrete size classes, i.e. the seed-lot heterogeneity in mass was reduced. Using this approach, the mortality curves had a steeper slope. Furthermore, data for 24 tropical tree species from the Database of Tropical Tree Seed Research (DABATTS) revealed that seed lots with less variability in mass had steeper mortality curves. Thus, taken together, the data suggest that, at least for whole seeds, the wide range of desiccation sensitivities typically inferred is an artefact of seed to seed variation in mass, and hence water contents, during drying.

An NMR microscopic study of grape (Vitis vinifera L.)

SummaryMature healthy grape berries and berries wound-inoculated with the fungusBotrytis cinerea were examined by1H NMR microimaging using 2D and 3D spin echo and gradient echo procedures. These NMR images were compared with representations obtained by conventional histology, where possible using the same specimens. 3D imaging datasets from excised seeds were reconstructed by surface rendering and maximum intensity projection to allow interpretation of their internal structure. T2-weighted spin echo images revealed the major features of the pericarp, septum and loculi of whole berries. T1-weighted images were less discriminatory of parenchyma tissues in the fruit but revealed the endosperm in seeds as a chemically shifted feature. A non-invasive study by T1-weighted spin echo NMR imaging of infection byB. cinerea over a 6-day period showed that the disease spread throughout the exocarp but failed to spread in the mesocarp, a result confirmed by histological examination of the same specimen. Surface rendering of 3D datasets of excised seeds revealed the two ruminations of the endosperm and the distal location of the chalaza. The position of the embryonic axis was revealed in T2-weighted maximum intensity projections. This noninvasive study revealed the need to apply a range of imaging techniques and parameters to visualise the structural features of the different parts of the grape berry.

In situ measurement of free radical formation during the thermal decomposition of grape seed oil using spin trapping and electron paramagnetic resonance spectroscopy

ZusammenfassungDie Erzeugung von freien Radikalen als Resultat des oxidativen Abbaues von Lipidmolekülen während des Erhitzens von Traubenkernöl wurde durch die Kombination von „spin trapping“ und elektronenparamagnetischer-Resonanz-(EPR)-Spektroskopie gezeigt. Die Auswirkungen der Temperatur auf die Geschwindigkeit des Entstehens und des Abbaus des Addukts mit der “spin trap”N-t-butyl-α-phenylnitron (PBN) wurde im Bereich von 105–180°C untersucht. Die Ergebnisse zeigen, daß für das Studium von Prozessen mit freien Radikalen in Ölen in situ im Hohlraum des Spektrometers bei Temperaturen bis zu 180°C PBN geeignet ist.AbstractThe generation of free radical intermediates as a result of the oxidative degradation of lipid molecules during the heating of grape seed oil has been established by a combination of “spin trapping” and electron paramagnetic resonance spectroscopy. The effects of temperature on the rates of formation and decomposition of the adduct with the spin trapN-t-butyl-α-phenylnitrone (PBN) have been investigated over the temperature range 105–180°C. The results show that PBN can be used for studies of free radical processes in oils in situ in the spectrometer cavity at temperatures up to 180°C.

The involvement of oxygen-derived free radicals in the resistant response of potato tubers toErwinia carotovora

SummaryThe absolute requirement of oxygen for a potato tuber (cv. Pentland Crown) to display a resistant response toErwinia carotovora has been demonstrated in EPR measurements. These show that a relatively stable free radical is formed in inoculated hosts only after exposure to air. In an attempt to isolate and identify unstable free radical precursors, experiments have been conducted in which the chemical spin trap α-(4-pyridyl 1-oxide)-N-tert-butyl-nitrone (POBN) was incorporated into the tissue either at the time of inoculation or upon exposure to air. A single radical adduct was observed with spectral parameters that resemble those of a lipid-derived radical.

Use of EPR and ENDOR spectroscopy in conjunction with the spin trapping technique to study the high-temperature oxidative degradation of fatty acid methyl esters†

Free radicals produced during the autoxidation of unsaturated edible oils are extremely short-lived, but are able to react with spin traps to produce adducts with sufficient stability for spectroscopic characterisation at (near) cooking temperatures (353–443 K). EPR spectra have shown that the model esters methyl oleate, linoleate and linolenate each formed three distinct radical adducts with N-tert-butyl-α-phenylnitrone (PBN). These adducts have been further characterised by obtaining spectra under conditions of limited oxygen availability and in the presence of α-tocopherol; two of these adducts corresponded to peroxyl and alkyl radical adducts of PBN, whereas the other was an alkyl adduct of 2-methyl-2-nitrosopropane (MNP), which was formed as a result of decomposition of the PBN peroxyl radical adduct. The origins of the various 1H hyperfine splittings have been determined by using selectively and fully deuterated PBN and selectively deuterated oleate and some of their magnitudes have been confirmed by ENDOR spectroscopy. The results obtained clearly confirm the high temperature oxidation of fatty acid esters to proceed via a different mechanism from that observed at low temperature, and point to significant differences in oxidation mechanisms of monounsaturated fatty acid esters relative to polyunsaturated.

Are free radical generation and phytoalexin biosynthesis coupled

The induction of plant defence mechanisms has been extensively studied in recent years and there appear to be three interdependent roles for free radicals in the host response (Sutherland 1991) viz ; oxidation of specific host components, which may include lipid peroxidation (Rogers et al . 1988) and cell wall lignification (Bolwell et al . 1985), direct injury to the pathogen, and signal transduction upon infection. A potential messenger role has been proposed for the short-lived hydroxyl radical, HO˙ (Epperlein et al . 1986) and the superoxide radical anion, O 2 − ˙ (Doke 1983; Doke et al . 1991). The present study has utilised EPR spectroscopy and spin trapping with α-(4-pyridyl l-oxide)-N- tert -butylnitrone (POBN) to investigate the free radical chemistry of soybean cotyledons during incompatible infection, abiotic elicitation and wounding.