Evolution of the Levels of Free Radicals Generated on Wheat Flour and Wheat Bran by Electron Beam

This paper presents the experimental data regarding the levels of free radicals investigated by electron spin resonance (ESR) on wheat flour and wheat bran exposed to an electron beam. Samples were irradiated with an electron linear accelerator of 6 MeV and then stored at room temperature in air. ESR spectra of the samples indicated presence of free radicals induced by electron beam. Three types of free radicals have been detected in wheat flour, and signals typical for cellulose‐like radicals have been noticed for wheat bran, their concentration increasing with the irradiation dose. The postirradiation storage of both sample types caused radical decay with a two‐step pattern associated with fast decay of short‐life radicals followed by slow reduction of long‐life radicals. However, in the first step, the irradiated wheat bran exhibited more rapid decay of radicals than irradiated flour owing to their different complex matrixes, which led to paramagnetic structures of different origin after exposure to an electron beam. The ESR technique allows the detection of free radicals induced in wheat flour and bran by electron beam for a limited period after irradiation that could be shorter than the shelf life of the products.     

ESR法定量检测干果类辐照食品

以葵花籽、核桃、开心果和榛子为试验材料,研究在0、1.0、3.0、5.0和10.0kGy剂量范围内4种样品辐照剂量与信号强度的关系以及相关性.结果表明:4种样品在辐照前后ESR波谱有明显区别,其信号强度与辐照剂量均呈正相关.辐照后样品的ESR强度和谱形都发生变化,应用ESR法能够鉴定4种食品是否经过辐照.其中核桃和开心...     

Free radical scavenging properties of conjugated linoleic acids.

Conjugated linoleic acids (CLA) were investigated for free radical scavenging properties against the stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH.) by electron spin resonance (ESR) spectrometry and spectrophotometric methods. ESR results demonstrated that CLA directly reacted and quenched free DPPH radicals in benzene, while spectrophotometric analysis showed the radical scavenging capacity of CLA in ethanol. Dose and time effects of CLA-DPPH. reactions were observed in both tests. The ED(50) of CLA was 18 mg/mL under experimental conditions. CLA are much weaker radical scavengers as compared to vitamin E, vitamin C, and BHT. Kinetics of CLA-DPPH. reactions was different to that of linoleic acid (LA)-DPPH. reactions. CLA reacted and quenched DPPH radicals at all tested levels without a lag phase, while LA had a lag phase and showed no radical quenching activity at levels of 5-80 mg/mL in 30 min. These data indicated that CLA can provide immediate protection against free radicals, but LA cannot.     

Status of free radicals in Indian monsooned coffee beans gamma-irradiated for disinfestation

Free radicals in two cultivars of Indian monsooned coffee beans, gamma-irradiated for hygienic and quarantine purposes, were examined by entrapping the small amount of samples in potassium chloride powder in ESR quartz tubes. In contrast to a prominent free radical signal at g = 2.002, observed in spermoderm (silver skin) and cotyledon (whole seed without skin) parts of normal coffee beans, the same was not discernible in monsooned coffee bean parts of both cultivars. The ESR signal was found to be more prominent in the spermoderm than in the whole seed portion of the normal coffee beans. Common practices of roasting and powdering were found to generate quantitatively more free radicals in coffee beans than gamma-irradiation alone. Phenols, contributing maximally to observed free radical signals in coffee beans, were significantly different in normal and monsooned coffee beans. These observations on insignificant free radical population in irradiated monsooned coffee beans may be attributed to their inherent possession of high water activity, favoring decay of free radicals produced. Textural studies with monsooned coffee beans, before and after mild heat treatments, supported these findings.     

In vivo ESR spin trapping detection of carbon-centered alpha-Farnesene radicals

Lyophilisates of the ascomycetes Penicillium solitum and Aspergillus niger converted alpha-farnesene to 7-hydroxyfarnesene as the major product. The radical mechanism of this bioconversion was proven by electron spin resonance (ESR) and GC-MS using the spin trapping technique. Intermediate carbon-centered radicals of alpha-farnesene were captured using two spin traps, 2-methyl-2-nitrosopropane and alpha-(4-pyridyl-1-oxide)- N- tert-butylnitrone, respectively. The evaluation of the coupling constants and hyperfine couplings of the ESR spectra showed that tertiary carbon radicals were trapped. The radical position at C7 of alpha-farnesene was derived from EI and CI mass spectra of the corresponding MNP spin adduct. The present study demonstrates that the complementary application of ESR and MS spectrometric data allows the detailed evaluation of a radical mechanism of a fungal terpene transformation reaction.     

Conjugated linoleic acid isomers differ in their free radical scavenging properties

Conjugated linoleic acid (CLA) isomers were investigated for free radical scavenging properties against the stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH(*)) by electron spin resonance (ESR) spectrometry and spectrophotometric methods. ESR measurements confirmed that both c9,t11-CLA and t10,c12-CLA directly reacted with and quenched DPPH radicals, whereas spectrophotometric analysis demonstrated that c9,t11-CLA and t10,c12-CLA differed in their kinetic and thermodynamic properties in reacting with DPPH radicals. t10,c12-CLA was shown to exhibit a greater initial velocity in CLA-DPPH radical reactions at levels of 2.5-80 mg/mL, and c9,t11-CLA scavenged more DPPH radicals at steady state. Similar dose and time relationships were observed for both isomers. In addition, a mixture of c9,t11- and t10,c12-CLA isomers demonstrated a greater initial velocity in quenching DPPH radicals than either isomer alone on the same concentration basis, suggesting that a synergistic effect between CLA isomers existed in their reactions with DPPH radicals. These results support the conclusion that individual CLA isomers differ in their biological actions and indicate that interaction(s) between isomers may contribute to their beneficial effects.     

Analysis of gamma-irradiated melon, pumpkin, and sunflower seeds by electron paramagnetic resonance spectroscopy and gas chromatography-mass spectrometry

Seeds of melon (Citrullus lanatus var. sp.), pumpkin (Cucurbita moschata), and sunflower (Heliantus annus) were gamma-irradiated at 1, 3, 5, and 10 kGy and analyzed by electron paramagnetic resonance (EPR) and gas chromatography-mass spectrometry (GC-MS) according to EN1787:2000 and EN1785:2003, respectively. Distinguishable triplet signals due to the presence of induced cellulose radicals were found at 2.0010-2.0047 g in the EPR spectra. The gamma-irradiated radiolytic markers of 2-dodecylcyclobutanone (2-DCB) and 2-tetradecylcyclobutanone (2-TCB) were identified in all irradiated seed samples. Both the free radicals and the alkylcyclobutanones were found to increase with irradiation dose. In general, linear relationships between the amount of radicals and irradiation dosage could be established. Studies at an ambient temperature (20-25 degrees C) in a humidity-controlled environment showed a complete disappearance of the cellulosic peaks for irradiated samples upon 60 days of storage. Such instability behavior was considered to render the usefulness of using EPR alone in the determination of irradiated seed samples. On the other hand, 2-DCB and 2-TCB were also found to decompose rapidly (>85% loss after 120 days of storage), but the radiolytic markers remained quantifiable after 120 days of postirradiation storage. These results suggest that GC-MS is a versatile and complimentary technique for the confirmation of irradiation treatment to seeds.     

EPR studies on gamma-irradiated barley seeds: identification of trapped electrons.

Electron paramagnetic resonance (EPR) studies were conducted on barley seeds exposed to normal (H(2)O) and deuterated (D(2)O) moisture, irradiated with 750 Gy at 77 K. Reported here, for the first time, are the trapped electrons formed on gamma-irradiation of seeds at 77 K. Electrons are stabilized/solvated with an increase in the moisture content (H(2)O/D(2)O) of seeds. The recombination of the trapped electron with radical cation gave intense thermoluminescence emission at 110 K. With the increase in temperature and the destruction of singlet, unmasking of an underlying heterogeneous population of free radicals was observed. These free radicals emanate mainly from the endosperm (approximately 95% by wt of the seed), whereas irradiated embryos show a broad multiplet of comparatively low amplitude. Radiolysis of carbohydrate, proteins (approximately 95% of endosperm), and lipids could possibly be responsible for the heterogeneous population of free radicals. Peroxyl radicals were also observed on annealing.     

Electron paramagnetic resonance in humic substances

Electron spin resonance (ESR) measurements of soil and its fractions (humic acids, fulvic acids, post-extraction residues and bitumens) were performed and particular attention given to free radicals of organic origin. For such radicals in soil, two lines with g factors 2.004 and 2.002 were observed. For all four fractions one line was observed. To obtain more information on the radical structure, the samples were carbonized. This allowed the different chemical structures of each of the two organic radicals to be differentiated. However, it was not possible to ascribe any definite structure to these radicals. Heat-treatment measurements indicated that the humification process shows some similarity to the process of carbonization at low temperature.     

Identification of irradiated cashew nut by electron paramagnetic resonance spectroscopy

Cashew nut samples were irradiated at gamma-radiation doses of 0.25, 0.5, 0.75, and 1 kGy, the permissible dose range for insect disinfestation of food commodities. A weak and short-lived triplet (g = 2.004 and hfcc = 30 G) along with an anisotropic signal (g perpendicular = 2.0069 and g parallel = 2.000) were produced immediately after irradiation. These signals were assigned to that of cellulose and CO 2 (-) radicals. However, the irradiated samples showed a dose-dependent increase of the central line (g = 2.0045 +/- 0.0002). The nature of the free radicals formed during conventional processing such as thermal treatment was investigated and showed an increase in intensity of the central line (g = 2.0045) similar to that of irradiation. Characteristics of the free radicals were studied by their relaxation and thermal behaviors. The present work explores the possibility to identify irradiated cashew nuts from nonirradiated ones by the thermal behaviors of the radicals beyond the period, when the characteristic electron paramagnetic resonance spectral lines of the cellulose free radicals have essentially disappeared. In addition, this study for the first time reports that relaxation behavior of the radicals could be a useful tool to distinguish between roasted and irradiated cashew nuts.     

茶树特异成分对辐照诱导自由基的作用

研究了茶树体内特异成分对辐照诱导自由基的作用。结果表明，辐照茶籽内自由基的增长趋势表现为乔木型大叶品种大于灌木型中、小叶品种，１０个品种茶籽内自由基的耗照剂量效应模型为ｙ＝ａｅ（－ｂ／ｘ）。茶树体内儿茶素、茶多酚、黄酮苷、咖啡碱等特异成分与其辐射敏感性及自由基含量变化密切相关。影响辐照茶树体内自由基消长的主要因子是儿茶素，其中（－）－没食子儿茶素没食子酸酯（ＥＧＣＧ）与自由基反应有浓度效应，在低浓度条件下，具有诱发产生自由基的作用，而在高浓度条件下，则有消除自由基的作用     

辐照对透明质酸抗氧化性及结构特性的影响

用0、1、3、5、8、10、20和40kGy剂量的60Co γ射线对透明质酸溶液进行辐照,研究了辐照对透明质酸分子量、黏度特性及抗氧化性的影响.结果表明:辐照后透明质酸的分子量和黏度特性随剂量的增加而降低;透明质酸对羟自由基(OH·)和超氧阴离子自由基(O2·)的清除率随剂量的增大逐渐减弱,对DPPH·自由基清除作用和...     

ESR波谱法及其他物理法检测淀粉类辐照食品

研究了ESR波谱技术检测淀粉类辐照食品的方法。测定不同剂量辐照处理的玉米粉、小麦粉和糯米粉的电子自旋共振（ESR）波谱。结果表明：未辐照和辐照样品的ESR波谱有明显区别,ESR信号强度随着样品辐照吸收剂量的增加而增强。利用ESR试验结果与电镜图像进行比较。利用ESR波谱技术能够鉴别出含淀粉类辐照食品（玉米粉、小麦粉和糯米粉）是否经过辐照。     

Free radical scavenging properties of wheat extracts

Three hard winter wheat varieties (Akron, Trego, and Platte) were examined and compared for their free radical scavenging properties and total phenolic contents (TPC). Free radical scavenging properties of wheat grain extracts were evaluated by spectrophotometric and electron spin resonance (ESR) spectrometry methods against stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH*) and radical cation ABTS*+ (2,2'-azino-di[3-ethylbenzthiazoline sulfonate]). The results showed that the three wheat extracts differed in their capacities to quench or inhibit DPPH* and ABTS*+. Akron showed the greatest activity to quench DPPH radicals, while Platte had the highest capacity against ABTS*+. The ED50 values of wheat extracts against DPPH radicals were 0.60 mg/mL for Akron, 7.1 mg/mL for Trego, and 0.95 mg/mL for Platte under the experimental conditions. The trolox equivalents against ABTS*+ were 1.31 +/- 0.44, 1.08 +/- 0.05, and 1.91 +/- 0.06 micromol/g of grain for Akron, Trego, and Platte wheat, respectively. ESR results confirmed that wheat extracts directly reacted with and quenched free radicals. The TPC were 487.9 +/- 927.8 microg gallic acid equivalents/g of grain. No correlation was observed between TPC and radical scavenging capacities for DPPH* and ABTS*+ (p = 0.15 and p > 0.5, respectively).     

Role of hydroxyl radicals and singlet oxygen in the formation of primary radicals in unsaturated lipids: a solid state electron paramagnetic resonance study

Primary radicals were generated by UV photolysis of samples of trilinolein, at 77 K and under a controlled atmosphere. The resulting EPR spectra clearly show that the amount of radicals is dependent on the purity of the lipid, the exposure to visible light in the presence of a photosensitizer and oxygen, and, finally, the presence of an antioxidant. These solid state EPR experiments indicate that if all of the elements for the production of singlet oxygen (Rose Bengal, molecular oxygen, and visible light) are not present, primary radicals are practically not generated. They also point out the various steps of the oxidation mechanism: formation of singlet oxygen, which reacts with the lipid to form a hydroperoxide; and photolytic formation of the hydroxyl radical, which reacts with the frozen lipid to generate primary lipidic radicals. This constitutes a new method for investigating lipid oxidation and studying the influence of photosensitizers and molecules that are likely to react with singlet oxygen.     

Elemental,functional infrared and free radical characterization of humic acid-type fungal polymers (melanins)

Summary Humic acid-type polymers (melanins) synthesized in culture media by the fungi Aspergillus glaucus, Eurotium echinulatum, Hendersonula toruloidea, Stachybotrys atra and Aspergillus sydowi were analysed for elemental composition, functional group content, infrared (IR) and electron spin resonance (ESR) properties. Results were discussed in comparison with range values referred for soil humic acids. The fungal polymers showed significant differences in carboxyl and nitrogen content and C/H atomic ratios, reflecting a different degree of condensation (aromaticity) among the various samples. IR analysis gave evidence of: (a) the predominant aromatic character of melanins from A. glaucus, E. echinulatum and H. toruloidea; (b) the high content of aliphatic and olefinic components of S. atra melanin; (c) the typical presence of amide bonds in the nitrogen-richest melanins from A. sydowi and H. toruloidea; and (d) the generally low amount of free carboxyl groups, which often appeared involved in hydrogen bonds. ESR spectra showed that all the melanins studied contained appreciable concentrations of organic free radicals of prevailing semiquinonic nature and of the same order of magnitude commonly measured in humic acids from soil and other sources. The free electron concentration was shown to be directly related to the C/H atomic ratio and to the degree of aromaticity shown by IR analysis. This indicated that the highest free radical content in the melanins from E. echinulatum and A. glaucus was associated with the highest presence of condensed aromatic structures. Humic acid-type polymers synthesized by soil fungi may, therefore, contribute to the total free radical content of soil humic substances and play important roles in all reactions involving free radicals in soils and related environments.     

Green tea polyphenols react with 1,1-diphenyl-2-picrylhydrazyl free radicals in the bilayer of liposomes: direct evidence from electron spin resonance studies

Free radical scavenging reactions of green tea polyphenols (GTP) were investigated with electron spin resonance (ESR) spectroscopy in the phospholipid bilayer of liposomes, using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical as a model. The results showed that (1) GTP reacts with DPPH radicals in the bilayer of liposomes of both 1-hexadecanoyl-2-[(cis,cis,cis,cis,cis,cis)-4,7,10, 13,16,19-docosahexaenoyl]-sn-glycero-3-phosphocholine (DHAPC) and 1, 2-di[cis-9-hexadecenoyl]-sn-glycero-3-phosphocholine) (DPPC); and (2) GTP protects DHAPC liposomes effectively from the oxidation initiated by DPPH radicals. These results provide direct evidence that GTP reacts with free radicals in the model membrane and support the hypothesis that GTP protects unsaturated phospholipids from oxidation by reacting directly with the radicals.     

Free radical scavenging activities measured by electron spin resonance spectroscopy and B16 cell antiproliferative behaviors of seven plants.

In an effort to discover new antioxidant natural compounds, seven plants that grow in France (most of them in the Limousin countryside) were screened. Among these plants, was the extensively studied Vitis vinifera as reference. For each plant, sequential percolation was realized with five solvents of increasing polarities (hexane, chloroform, ethyl acetate, methanol, and water). Free radical scavenging activities were examined in different systems using electron spin resonance (ESR) spectroscopy. These assays were based on the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), the hydroxyl radicals generated by a Fenton reaction, and the superoxide radicals generated by the X/XO system. Antiproliferative behavior was studied on B16 melanoma cells. ESR results showed that three plants (Castanea sativa, Filipendula ulmaria, and Betula pendula) possessed, for the most polar fractions (presence of phenolic compounds), high antioxidant activities in comparison with the Vitis vinifera reference. Gentiana lutea was the only one that presented a hydroxyl scavenging activity for the ethyl acetate and chloroform fractions. The antiproliferative test results showed that the same three plants are the most effective, but for the apolar fractions (chloroform and hexane).     

Catechin transformation as influenced by aluminum

Polyphenols (catechins) are vital biomolecules in tea plants (Camellia sinensis), which are well-known as typical Al accumulators. However, the interaction between Al and catechin remains obscured. The objective of the present study was to investigate the effect of Al on the transformation of (+)-catechin. Solutions with OH/Al molar ratios of 2.5 (pH 5.5) and 3.0 (pH 7.0) prepared at Al/catechin molar ratios (R) of 0, 0.2, 0.4, 0.6, 0.8, and 1.0 were aged for 7 and 30 days, respectively. The precipitates were collected and examined by wet chemistry, X-ray diffraction, transmission electron microscopy, electron spin resonance (ESR), cross-polarization magic angle (CPMAS) 13C nuclear magnetic resonance (13C NMR) analyses, and Fourier transformation infrared absorption spectrometry (FT-IR). The weight of the precipitates increased with increasing Al/catechin molar ratios and with prolonged aging. The molar ratios of Al/catechin in the precipitates increased with increasing initial Al/catechin molar ratios and were close to the initial solution Al/catechin molar ratios. The chemical analysis and spectroscopic studies indicated that Al was bonded with catechin, forming a 1:1 type complex. The reaction of crystalline catechin with Al resulted in the formation of X-ray noncrystalline precipitates. The solid-state CPMAS 13C NMR spectra of the precipitates show the change in chemical shifts of catechin as a result of catechin complexation with Al. The FT-IR spectra of the Al-catechin precipitates also show the loss of absorption bands of several functional groups compared with catechin. The FT-IR data substantiate this reasoning. The ESR spectra of the precipitates show a single symmetrical line devoid of any fine splitting, indicating the presence of free radicals of semiquinones, which are commonly present in humified materials.     

Degradation of the coffee flavor compound furfuryl mercaptan in model Fenton-type reaction systems

The stability of the coffee flavor compound furfuryl mercaptan has been investigated in aqueous solutions under Fenton-type reaction conditions. The impact of hydrogen peroxide, iron, ascorbic acid, and ethylenediaminetetraacetic acid was studied in various combinations of reagents and temperature. Furfuryl mercaptan reacts readily under Fenton-type reaction conditions, leading to up to 90% degradation within 1 h at 37 degrees C. The losses were lower when one or more of the reagents was omitted or the temperature decreased to 22 degrees C. Volatile reaction products identified were mainly dimers of furfuryl mercaptan, difurfuryl disulfide being the major compound. In addition, a large number of nonvolatile compounds was observed with molecular masses in the range of 92-510 Da. The formation of hydroxyl and carbon-centered radicals was indicated by electron paramagnetic resonance spectra using alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide as spin traps. Whereas *OH was generated by Fenton-type reactions, the C-centered radical is probably a secondary product of the reaction of *OH with various organic molecules, the reaction with furfuryl mercaptan appearing to be the most important. No evidence for S-centered radicals was seen in the spin-trapping experiments, but a sulfur-containing radical was detected when measurements were made at 77 K in the absence of spin traps.