Effects of structure on radical-scavenging abilities and antioxidative activities of tea polyphenols: NMR analytical approach using 1,1-diphenyl-2-picrylhydrazyl radicals

Tea (Camellia sinensis) leaves contain various antioxidants such as ascorbic acid (1) and polyphenols. This study tries to clarify the molecular mechanisms underlying the antioxidative and radical-scavenging activities of these antioxidants, and the reactivities of each antioxidant have been compared against that of the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH, 2) using nuclear magnetic resonance (NMR) analysis. Catechol (3) and (+)-taxifolin (4) were oxidized to o-quinone by 2. However, ethyl protocatechuate (5) and quercetin (6) were not oxidized to o-quinone, even though they possess a catechol structure. The radical-scavenging ability of o-dihydroxyl phenolic compounds with a conjugated olefinic double bond (e.g., 6) was superior to that of compounds without this bond (e.g., 4), whereas the ability of o-dihydroxyl phenolic compounds possessing a conjugated carbonyl bond (5) was inferior to that of compounds lacking this bond (3). Vicinal trihydroxyl phenolic compounds with a conjugated olefinic double bond [e.g., myricetin (7)] had an inferior scavenging ability as compared with compounds lacking this bond [e.g., pyrogallol (8)], but 7 was a better scavenger than compounds with a conjugated carbonyl double bond [e.g., ethyl gallate (9)]. In addition, vicinal trihydroxyl phenolic compounds (e.g., 9) were superior to o-dihydroxyl phenolic compounds (e.g., 6). Finally, 1 scavenged radicals more quickly than 8.     

Aging of whiskey increases 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity

1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of Japanese whiskey after various aging periods in oak barrels was measured to evaluate the antioxidative effects of whiskey. The activity of the whiskey increased with the aging period with high correlation. The activity of various types of whiskey was measured and shown to be correlated to the potentiation of the GABAA receptor response measured in a previous paper. However, the fragrant compounds in the whiskey which potentiated the GABAA receptor response had low DPPH radical scavenging activity, while phenol derivatives had high radical scavenging activity. The whiskey was extracted by pentane. The aqueous part showed the scavenging activity, whereas the pentane part did not. Thus, both the DPPH radical scavenging activity and the potentiation of the GABAA receptor response increased during whiskey aging in oak barrels, but were due to different components. The whiskey protected the H2O2-induced death of E. coli more than ethanol at the same concentration as that of the whiskey. The changes that occurred in the whiskey during aging may be the reason aged whiskies are so highly valued.     

Inhibitory effects of citrus essential oils and their components on the formation of N-nitrosodimethylamine

Twenty-eight kinds of citrus essential oils and their components were studied for inhibitory effects on the formation of N-nitrosodimethylamine (NDMA). The reaction mixture consisted of dimethylamine and sodium nitrite adjusted at pH 3.6, in addition to essential oils and an emulsifying agent. The quantification was determined by high-performance liquid chromatography monitored at 220 nm. All of the essential oils inhibited the formation of NDMA in the range of 20-85%. The oils of ujukitsu (Citrus ujukitsu Hort. ex Shirai), yuzu (C. junos Tanaka), mochiyu (C. inflata Hort. ex Tanaka), and ponkan (C. reticulata Blanco cv. F-2426) inhibited the formation of NDMA much more effectively than other citrus oils. The inhibitory proportions of components of citrus essential oils such as myrcene, alpha-terpinene, and terpinolene were as high as 80%.     

NMR analytical approach to clarify the molecular mechanisms of the antioxidative and radical-scavenging activities of antioxidants in tea using 1,1-diphenyl-2-picrylhydrazyl

(+)-catechin, ethyl gallate, ascorbic acid, and alpha-tocopherol were reacted with 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the reaction mixtures were subjected to 13C-nuclear magnetic resonance (NMR) analyses to clarify the molecular mechanisms of the antioxidative and radical-scavenging activities of each antioxidant. When ascorbic acid was reacted with DPPH, it was oxidized to dehydroascorbic acid by DPPH. When a mixture of ascorbic acid and (+)-catechin was reacted with DPPH, ascorbic acid scavenged DPPH radical faster than (+)-catechin. Ascorbic acid also scavenged DPPH radical faster than ethyl gallate and alpha-tocopherol. When (+)-catechin was reacted with DPPH, the B-ring of (+)-catechin changed to an o-quinone structure. However, it was reduced to (+)-catechin by ethyl gallate or alpha-tocopherol. alpha-Tocopherol and ethyl gallate had almost identical antioxidative activities. Therefore, the order of radical-scavenging ability (speed) suggested by our 13C NMR study was as follows: ascorbic acid > alpha-tocopherol = ethyl gallate > (+)-catechin.     

Lipolytic effects of citrus peel oils and their components

This study was conducted to determine the lipolytic effects of eight kinds of citrus peel oils and their components. All of the citrus peel oils revealed lipolytic effects on olive oil model solution ranging from 10.9 to 73.8%. Hakyul (Citrus natsudaidai Hayata) showed the highest lipolytic effect (73.8%), followed by yuza (Citrus junos Sieb. ex Tanaka, 68.1%) and lemon (Citrus limonium, 63.4%), and their effects were comparable with or stronger than that of 5 mM raspberry ketone (p < 0.05). Among 17 authentic compounds relating to citrus peel oils, octanal (78.6%) showed the highest lipolytic effect, followed by gamma-terpinene (76.3%), limonene (75%), terpinen-4-ol (70.7%), nerol (69.9%), p-cymene (67.7%), and geranyl acetate (67.2%), and their effects were stronger than that of 5 mM raspberry ketone (p < 0.05). Ethyl acetate, alpha-pinene, myrcene, citronellal, linallyl acetate, and citronellol exhibited poor lipolytic effect in the model solution. Lipolytic effect was found to be high when the oils included a higher content of gamma-terpinene and p-cymene. Limonene showed potential lipolytic effect, and its effect is likely to be enhanced by the presence of gamma-terpinene and p-cymene. It is considered that monoterpene hydrocarbons consisting of one or two double bonds would have stronger lipolytic effect than those having three double bonds.     

Tyrosinase inhibitory activity of citrus essential oils

Thirteen kinds of citrus essential oils and their volatile flavor constituents were investigated for tyrosinase inhibitory activity. Eureka lemon, Lisbon lemon, Keraji, and Kiyookadaidai significantly inhibited the oxidation of L-dihydroxy phenylalanine (L-DOPA) by mushroom tyrosinase. Citral and myrcene among volatile flavor constituents of citrus essential oils exhibited tyrosinase inhibitory activities with Ki values of 0.318 and 2.38 mM, respectively. The inhibition kinetics analyzed by a Lineweaver-Burk plot indicated that citral is a noncompetitive inhibitor and myrcene is a competitive inhibitor. These results indicated that citral and myrcene are responsible for the tyrosinase inhibitory activity of citrus essential oils.     

Characterization of the total free radical scavenger capacity of vegetable oils and oil fractions using 2,2-diphenyl-1-picrylhydrazyl radical

The total free radical scavenger capacity (RSC) of 57 edible oils from different sources was studied: olive (24 brands of oils), sunflower (6), safflower (2), rapeseed (3), soybean (3), linseed (2), corn (3), hazelnut (2), walnut (2), sesame (2), almond (2), mixture of oils for salad (2), "dietetic" oil (2), and peanut (2). Olive oils were also studied according to their geographical origins (France, Greece, Italy, Morocco, Spain, and Turkey). RSC was determined spectrophotometrically by measuring the disappearance of the radical 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(*)) at 515 nm. The disappearance of the radical followed a double-exponential equation in the presence of oils and oil fractions, which suggested the presence of two (fast and slow) groups of antioxidants. RSC was studied for the methanol-soluble phase ("methanolic fraction", MF) of the oil, the fraction nonsoluble in methanol ("lipidic fraction", LF), and the nonfractionated oil ("total oil"; TF = MF + LF). Only olive, linseed, rapeseed, safflower, sesame, and walnut oils showed significant RSC in the MF due to the presence of phenolic compounds. No significant differences were found in the RSC of olive oils from different geographical origins. Upon heating at 180 degrees C the apparent constant for the disappearance of RSC (k(T)) and the half-life (t1/2) of RSC for MF, LF, and TF were calculated. The second-order rate constants (k2) for the antiradical activity of some phenolic compounds present in oils are also reported.     

Contamination of Italian citrus essential oils: presence of chloroparaffin

In this study, the contamination by chloroparaffin of Sicilian and Calabrian citrus essential oils, produced in the crop years 1994-1996, was investigated. The analyses were carried out on 102 lemon oils, 98 orange oils, and 96 mandarin oils, using a dual-channel GC-ECD. It was found that 53% of lemon oil, 33% of orange oil, and 38% of mandarin oil samples were contaminated. The mean contamination levels were 7.1 ppm (lemon), 2.5 ppm (orange), and 5.3 ppm (mandarin). The highest concentration of chloroparaffin found was 60 ppm in a lemon oil sample.     

Improved in vitro assays of superoxide anion and 1,1-diphenyl- 2-picrylhydrazyl (DPPH) radical-scavenging activity of isoflavones and isoflavone metabolites

Free radical-scavenging activity of isoflavones and some isoflavone metabolites have been described previously, but the results are inconsistent. The objective of the present study was to find out the pivotal factors that influence an accurate detection of both superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity. We here showed for the first time that organic solvents, including methanol, ethanol and acetone, were of strong superoxide radical-scavenging activity at concentrations down to 0.1% (v/v), however, no such activity was observed with acetonitrile at concentrations up to 2.0% (v/v). In DPPH assay, we found that the DPPH radical-scavenging ratio increased together with the extended reaction time. Based on our findings, improved in vitro assays for the detection of radical-scavenging activity of both isoflavones (daidzein and genistein) and isoflavone metabolites, including dihydrodaidzein (DHD), dihydrogenistein (DHG), and O-desmethylangolensin (O-Dma), were established.     

Continuous hot pressurized solvent extraction of 1,1-diphenyl-2-picrylhydrazyl free radical scavenging compounds from Taiwan yams (Dioscorea alata)

This study investigates a semicontinuous hot pressurized fluid extraction process and the scavenging activity on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical of the extract from Taiwan yams (Dioscorea alata). Liquid-liquid extractions were preliminarily employed to generate six fractions, initially extracted by ethanol. Then, the aqueous solution of dried crude ethanol extract was sequentially fractionated by hexane, chloroform, ethyl acetate, and n-butanol. The EC50 value was defined as the UV absorption of DPPH concentrations sufficiently decreased to 50% of the original value. It was found that all peel portions have a better effect on scavenging of the DPPH free radical than meat portions, especially for the ethyl acetate partition of the peel portion of Tainung #2 yam. Its EC50 value (14.5 microg mL(-1)) was even lower than that of ascorbic acid (21.4 microg mL(-1)). Furthermore, semicontinuous hot pressurized ethanol was superior to hot pressurized water in extracting the compound scavenging the DPPH radical from the Purpurea-Roxb peel. The recovery of four unknown compounds corresponded to the scavenging ratio of DPPH free radical in the hot pressurized ethanol extract. Finally, three-level and four-factor experimental design revealed that ethanol ratio and temperature were the most effective factors in order. Conditions of 80% of aqueous ethanol, 20.0 kg/kg solid ratio, 180 psig (1.342 MPa), and 100 degrees C were preferred to extract those antioxidants from the yam peel.     

Antibacterial activities of plant essential oils and their components against Escherichia coli O157:H7 and Salmonella enterica in apple juice

We evaluated 17 plant essential oils and nine oil compounds for antibacterial activity against the foodborne pathogens Escherichia coli O157:H7 and Salmonella enterica in apple juices in a bactericidal assay in terms of % of the sample that resulted in a 50% decrease in the number of bacteria (BA(50)). The 10 compounds most active against E. coli (60 min BA(50) range in clear juice, 0.018-0.093%) were carvacrol, oregano oil, geraniol, eugenol, cinnamon leaf oil, citral, clove bud oil, lemongrass oil, cinnamon bark oil, and lemon oil. The corresponding compounds against S. enterica (BA(50) range, 0.0044-0.011%) were Melissa oil, carvacrol, oregano oil, terpeineol, geraniol, lemon oil, citral, lemongrass oil, cinnamon leaf oil, and linalool. The activity (i) was greater for S. enterica than for E. coli, (ii) increased with incubation temperature and storage time, and (iii) was not affected by the acidity of the juices. The antibacterial agents could be divided into two classes: fast-acting and slow-acting. High-performance liquid chromatography analysis showed that the bactericidal results are related to the composition of the oils. These studies provide information about new ways to protect apple juice and other foods against human pathogens.     

Contamination of Italian citrus essential oils: presence of phthalate esters.

Contamination by phthalate esters of Sicilian and Calabrian citrus essential oils, produced in the crop years 1994-1996, was investigated using a GC-MS system with direct injection of the samples. A total of 35 lemon oils, 31 orange oils, and 21 mandarin oils were analyzed. Diisobutyl phthalate and/or bis(2-ethylhexyl) phthalate were found in almost all samples, while di-n-butyl phthalate was present in 8. Concentrations up to a maximum of 62 ppm were found for diisobutyl phthalate and up to a maximum of 29.9 ppm for bis(2-ethylhexyl) phthalate.     

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.     

Comparison of fast and conventional GC analysis for citrus essential oils

This investigation concerns the application of fast GC in the analysis of essential oils. These are complex matrixes that usually undergo GC separation with conventional methods involving long columns, slow programmed temperature rates, and consequently, a high cost in terms of time. Fast GC techniques are based on the use of narrow bore capillary columns that allow the achievement of high-speed separations on complex samples while maintaining excellent resolution. This work saw the application of two methods on five different citrus essential oils and the comparison of all the results obtained.     

Production process contamination of citrus essential oils by plastic materials

Twelve samples of plastic materials employed in the industrial extraction of citrus essential oils were analyzed for the presence of phosphorated plasticizers, chloroparaffins, and phthalate esters. The samples tested were found to release these contaminants into the essential oils during the production process. Contamination tests were carried out using dichloromethane and uncontaminated samples of citrus essential oils as extractants. The extracts were analyzed by HRGC/FPD, ECD, and MS. Only one sample of plastic material was found to release triaryl phosphates, 5 samples released chloroparaffins, 6 released diisobutyl phthalate, and 8 released bis(2-ethylhexyl) phthalate. Significantly larger quantities of contaminants were released by new plastic parts than by used plastic parts.     

Antioxidant activities and volatile constituents of various essential oils

Thirteen essential oils were examined for their antioxidant activity using three different assay systems. Jasmine, parsley seed, rose, and ylang-ylang oils inhibited hexanal oxidation by over 95% after 40 days at a level of 500 microg/mL in the aldehyde/carboxylic acid assay. Scavenging abilities of the oils for the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical ranged from 39% for angelica seed oil to 90% for jasmine oil at a level of 200 microg/mL. The greatest inhibitory activity toward malonaldehyde (MA) formation from squalene upon UV-irradiation was obtained from parsley seed oil (inhibitory effect, 67%), followed by rose oil (46%), and celery seed oil (23%) at the level of 500 microg/mL. The main compounds of oils showing high antioxidant activity were limonene (composition, 74.6%) in celery seed, benzyl acetate (22.9%) in jasmine, alpha-pinene (33.7%) in juniper berry, myristicin (44%) in parsley seed, patchouli alcohol (28.8%) in patchouli, citronellol (34.2%) in rose, and germacrene (19.1%) in ylang-ylang.     

Determination of some heavy metals and selenium in Sicilian and Calabrian citrus essential oils using derivative stripping chronopotentiometry

This paper aims to bring some novelty about the concentration of some heavy metals and selenium in biological citrus essential oils (CEO) produced in Sicily and Calabria in different crop years. Derivative stripping chronopotentiometry has been used as an accurate, sensitive, and rapid technique for the determination of Cd, Cu, Mn, Ni, Pb, Zn, and Se in hydrochloric acid extracts of CEO; in the optimized electrochemical conditions, detection limits of <1 microg kg(-1) were obtained for all of the studied metals. In particular, the concentrations of metals were determined in biological bergamot essential oils produced in Calabria in 1999 and 2000 and in biological CEO produced in Sicily in 2003 and 2004. The obtained results provided evidence that Mn was the most abundant metal in all of the studied CEO followed by Zn, Ni, Cu, Pb, and Se; Cd concentrations were always lower than the limit of detection (0.6 microg kg(-1)).     

In vivo antioxidant activities of essential oils and their constituents from leaves of the Taiwanese Cinnamomum osmophloeum

Cinnamomum osmophloeum Kaneh is an indigenous tree species in Taiwan. In this study, phytochemical characteristics and antioxidant activities of the essential oils and key constituents from the leaves of two C. osmophloeum clones were investigated. The two trees possess two chemotypes, which were classified as the cinnamaldehyde type and camphor type. We demonstrated that the essential oils from C. osmophloeum leaves exerted in vivo antioxidant activities in Caenorhabditis elegans. In addition, trans-cinnamaldehyde and D-(+)-camphor, which respectively represent the major compounds in the cinnamaldehyde-type and camphor-type trees, exerted significant in vivo antioxidant activities against juglone-induced oxidative stress in C. elegans. Moreover, expressions of antioxidative-related genes, including superoxide dismutase (SOD) and glutathione S-transferase (GST), were significantly induced by trans-cinnamaldehyde and D-(+)-camphor from C. osmophloeum leaves. Our results showed that the essential oils from C. osmophloeum leaves and their major compounds might have good potential for further development as nutraceuticals or antioxidant remedies.     

Composition of the essential oils of Thymus and Origanum species from Algeria and their antioxidant and antimicrobial activities

The composition of the essential oils of Origanum and Thymus species restricted to Algeria and the North Africa region was determined. Antioxidant and antibacterial activities of the isolated essential oils were also determined. The oils of oregano plants were strongly characterized by p-cymene (16.8-24.9%), gamma-terpinene (16.8-24.9%), thymol (8.4-36.0%), and carvacrol (1.1-29.7%), a thymol chemotype for Origanum floribundum and a alpha-terpineol chemotype for Thymus numidicus being described for the first time. The strains of Listeria monocytogenes tested were relatively resistant to the action of essential oils of either Origanum or Thymus species. All essential oils possessed antioxidant activity, but this was dependent on the specific chemical composition and the method employed to determine such activity.     

Antitermitic activity of leaf essential oils and components from Cinnamomum osmophleum

The antitermitic activities of the essential oils from the leaves of two Cinnamomum osmophloeumclones (A and B) and their chemical ingredients against Coptotermes formosanus Shiraki were investigated according to direct contact application. Results from this experiment have demonstrated that the indigenous cinnamon B leaf essential oil has a more effective antitermitic activity than indigenous cinnamon A leaf essential oil. Furthermore, when cinnamaldehyde, eugenol, and alpha-terpineol are extracted from indigenous cinnamon leaf essential oil and used at the strength of 1 mg/g, their antitermitic effectiveness is much higher than that using indigenous cinnamon leaf essential oil. Among the congeners of cinnamaldehyde examined, cinnamaldehyde has exhibited the strongest termiticidal property.