Free Radical Scavenging and Cellular Antioxidant Properties of Astaxanthin

Astaxanthin is a coloring agent which is used as a feed additive in aquaculture nutrition. Recently, potential health benefits of astaxanthin have been discussed which may be partly related to its free radical scavenging and antioxidant properties. Our electron spin resonance (ESR) and spin trapping data suggest that synthetic astaxanthin is a potent free radical scavenger in terms of diphenylpicryl-hydrazyl (DPPH) and galvinoxyl free radicals. Furthermore, astaxanthin dose-dependently quenched singlet oxygen as determined by photon counting. In addition to free radical scavenging and singlet oxygen quenching properties, astaxanthin induced the antioxidant enzyme paroxoanase-1, enhanced glutathione concentrations and prevented lipid peroxidation in cultured hepatocytes. Present results suggest that, beyond its coloring properties, synthetic astaxanthin exhibits free radical scavenging, singlet oxygen quenching, and antioxidant activities which could probably positively affect animal and human health.     

Antioxidant properties of phenolic compounds in macadamia nuts

Phenolic compounds in macadamia nuts and shells were identified, and their antioxidant activities were evaluated in refined macadamia nut oil. Thin-layer chromatography of oil extracted from macadamia nut kernels and shells indicated the possible presence of catechol, phrogallol, and 3,4,5-trihydroxy phenolic compounds. Four phenolic compounds were tentatively identified as 2,6-dihydroxybenzoic acid, 2′-hydroxy-4′-methoxyacetophenone, 3′,5′-dimethoxy-4′-hydroxyacetophenone, and 3,5-dimethoxy-4-hydroxycinnamic acid. Adding 0.01% of 2′-hydroxy-4′-methoxyacetophenone, 3′,5′-dimethoxy-4′-hydroxyacetophenone, or 3,5-dimethoxy-4-hydroxycinnamic acid to the oil significantly increased the Rancimat induction time against the control (P<0.0001). At this concentration, 3′,5′-dimethoxy-4′-hydroxyacetophenone was the most effective compound added. Although induction times of oils with 0.01%, 2,6-dihydroxybenzoic acid were not significantly different from the control, at 0.1% there was a significant difference from the control (P<0.0001). The activity was the same as that of 2′-hydroxy-4′-methoxyacetophenone at 0.1%.     

Identification of phenolic compounds and antioxidant activity of guava dehydrated by different drying methods

Abstract

The influence of different drying techniques on guava was investigated, including phenolic components and antioxidant activities. Through drying processes, total phenolic content (TPC) increased and formation of small molecular phenolic acids (multi-methoxy benzoic acid and sinapic acid) was promoted. UPLC-ESI-QTOF-MS determination showed flavanol compounds, hydrolyzable tannins, ellagic acid conjugates and cinnamic acid derivatives were four predominant phenolics of guava. Drying treatments caused degradation of catechin and its derivatives. Contrarily, drying treatments contributed to higher contents of procyanidin trimers. Moreover, thermal drying treatments led to degradation of macromolecular tannins and formation of smaller molecular tannins and ellagic acid conjugates, while simultaneously reduced the stabilities of most intrinsic ellagic acid conjugates. Furthermore, drying processes increased the yield of cinnamic acid dihexose, probably generating from lignin or phenolics–carbohydrate complex. Freeze drying and hot air drying showed better performance on retention of TPC and enhancement of antioxidant activity (AA).     

Antioxidant activity of tocopherols and phenolic compounds of virgin olive oil

The antioxidant effects of hydrophilic phenols and tocopherols on the oxidative stability in virgin olive oils and in purified olive oil have been evaluated. Total hydrophilic phenols and the oleosidic forms of 3,4-dihydroxyphenolethanol (3,4-DHPEA) were correlated (r=0.97) with the oxidative stability of virgin olive oil. On the contrary, tocopherols showed low correlation (r=0.05). Purified olive oil with the dialdehydic form of elenolic acid linked to 3,4-DHPEA, an isomer of oleuropeine aglycon, and 3,4-DHPEA had good oxidative stability. A synergistic effect was observed in the mixture of 3,4-DHPEA and its oleosidic forms with α-tocopherol in purified olive oil by the Rancimat method at 120°C.     

Antioxidant activity of brazilian vegetables and its relation with phenolic composition

Vegetables are widely consumed in Brazil and exported to several countries. This study was performed to evaluate the phenolic content and antioxidant activity of vegetables commonly consumed in Brazil using five different methods, namely DPPH and ABTS free radical, β-carotene bleaching, reduction of Fe³⁺ (FRAP), oxidative stability in Rancimat, and the chemical composition using gas chromatography-mass spectrometry (GC-MS). The content of phenolic compounds ranged from 1.2 mg GA/g (carrot) to 16.9 mg GA/g (lettuce). Vegetables presenting the highest antioxidant activity were lettuce (77.2 μmol Trolox/g DPPH^•; 447.1 μmol F²⁺/g FRAP), turmeric (118.6 μmol Trolox/g ABTS^•+; 92.8% β-carotene), watercress and broccoli (protective factor 1.29—Rancimat method). Artichoke, spinach, broccoli, and asparagus also showed considerable antioxidant activity. The most frequent phenolic compounds identified by GC-MS were ferulic, caffeic, p-coumaric, 2-dihydroxybenzoic, 2,5-dihydroxybenzoic acids, and quercetin. We observed antioxidant activity in several vegetables and our results point out their importance in the diet.     

Antioxidant activity of phenolic compounds in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose

The aim of this work was to study the evolution of oxidation and the efficiency of phenolic antioxidants in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose (Cas‐Lac) or stabilized by Tween‐20 (T‐20). Two groups of phenolic antioxidants which are structurally similar were tested, i.e. (1) α‐tocopherol and its water‐soluble analogue, Trolox; and (2) gallic acid and its ester derivatives propyl gallate and dodecyl gallate. Emulsion samples were oxidized at 40 °C and the progress of oxidation was followed through quantitation of oxidized triacylglycerol monomers, dimers and oligomers. Results showed that Cas‐Lac emulsions were more stable to oxidation than T‐20 emulsions. In both types of emulsions, the most protective antioxidants were the compounds of lower polarity, namely, α‐tocopherol and dodecyl gallate. It was also found that substantial amounts of α‐tocopherol coexisted with significant polymerization, which was indicative of the heterogeneity of oxidation, i.e. differences of oxidation rate in oil droplets.     

Inhibition of lipid peroxidation by anthocyanins,anthocyanidins and their phenolic degradation products

Food components that delay or prevent biomolecule oxidation may be relevant in shelf life extension as well as disease prevention. Anthocyanins are a potentially important group of compounds, but they are prone to degradation both in vitro and in vivo, producing simple phenols. In this study, eight structurally related (poly)phenols [anthocyan(id)ins and phenolic acids] were examined for their ability to inhibit lipid oxidation at physiologically relevant concentrations (100–1000 nM) using the Cu²⁺‐mediated low‐density lipoprotein oxidation model. Interaction between each (poly)phenol and Cu²⁺ ions was also investigated. (Poly)phenols with an ortho‐dihydroxy group arrangement, i.e. cyanidin‐3‐glucoside, cyanidin and protocatechuic acid, were the most effective within their class, extending the lag phase to oxidation by 137, 255 and 402%, respectively (at 1000 nM). At the same concentration, trihydroxy‐substituted compounds (delphinidin and gallic acid) were of intermediate efficacy, extending the lag phase by 175 and 38%, respectively. Compounds with the 4'‐hydroxy‐3',5'‐methoxy arrangement (i.e. malvidin‐3‐glucoside and malvidin) were the least effective (3 and 58% extension, respectively), while syringic acid (4‐hydroxy‐3,5‐dihydroxy benzoic acid) was pro‐oxidant (lag phase shortened by 31%). (Poly)phenols with the ortho‐dihydroxy arrangement chelated Cu²⁺ ions, which in part explains their greater efficacy over the other (poly)phenols in this model oxidation system. However, differences in their hydrogen‐donating properties and their partitioning between lipid and hydrophilic phases are also relevant in explaining these structure‐activity relationships.     

Antioxidant activity and active sites of phospholipids as antioxidants

Various compounds, representative of the major functional groups in phospholipids, phosphatidylethanolamine and phosphatidylcholine, were tested for antioxidant activity (AA) in a sardine oil system to determine the relationship between molecular structure and the AA of these compounds. AA was found to be attributable not only to the side-chain amino groups but also to the cooperative effect of the hydroxy group in the side chain. Choline and ethanolamine, side-chain moieties of phospholipids, strongly inhibited increases in peroxide values in a sardine oil mixture during storage; however, phosphatidic acid derivatives and glycerol, also major functional groups of phospholipids, did not show AA. Choline and ethanolamine have hydroxy amines as functional groups; therefore, several model reagents that contained amines and alcohols were assayed to compare the activity of the amino group with that of the hydroxy group. All basic alkylamines examined had AA as decomposers of hydroperoxides. The intramolecular hydroxy group in these amines complemented AA of the amino group. Only intramolecular alcohol, which can donate a proton, showed strong synergistic activity with AAof the basic amines, while protected groups, such as methyl ether and phosphate ester, did not show this effect.     

Extracts of phenolic compounds from seeds of three wild grapevines-comparison of their antioxidant activities and the content of phenolic compounds

Phenolic compounds were extracted from three wild grapevine species: Vitis californica, V. riparia and V. amurensis seeds using 80% methanol or 80% acetone. The total content of phenolic compounds was determined utilizing the Folin-Ciocalteu’s phenol reagent while the content of tannins was assayed with the vanillin and BSA precipitation methods. Additionally, the DPPH free radical scavenging activity and the reduction power of the extracts were measured. The RP-HPLC method was applied to identify the phenolic compounds in the extracts, such as phenolic acids and catechins. The seeds contained large amounts of tannins, catechins and gallic acid and observable quantities of p-coumaric acid. The total content of phenolic compounds and tannins was similar in the extracts from V. californica and V. riparia seeds. However, the total content of total phenolic compounds and tannins in the extracts from V. californica and V. riperia seeds were about two-fold higher than that in the extracts from V. amurensis seeds. Extracts from seeds of the American species (V. californica and V. riparia) contained similarly high concentrations of tannins, whereas extracts from seeds of V. amurensis had approximately half that amount of these compounds. The content of catechin and epicatechin was similar in all extracts. The highest DPPH^• anti-radical scavenging activity was observed in the acetonic and methanolic extracts of V. californica and V. riparia seeds— while the acetonic extract from the V. californica seeds was the strongest reducing agent.     

Peroxyl and hydroxyl radical scavenging activity of some natural phenolic antioxidants

The autoxidation of linoleic acid dispersed in an aqueous media and the antioxidant effect of hydroxytyrosol, oleuropein, caffeic acid and tyrosol were studied. Linoleic acid autoxidation rate was estimated by the increase of conjugated diene level and by the decrease of linoleic acid content in the samples. The phenolic compounds exhibited an antioxidant activity which increased in the order: tyrosol < caffeic acid < oleuropein < hydroxytyrosol. The analysis of the hydroperoxide isomers pointed out that hydroxytyrosol, oleuropein and caffeic acid at a concentration of 10⁻⁴M inhibited the formation oftrans- trans isomers in the increasing order: caffeic acid < oleuropein < hydroxytyrosol. This inhibition could be related to the ability of phenolic compounds to scavenge peroxyl radical. Tyrosol did not inhibit the formation oftranstrans isomers. Phenolic compounds were degraded as a consequence of their antioxidant activity and their degradation rate was positively correlated to their antioxidant efficacy. These phenolic compounds, at a concentration of 6 × 10⁻³M, also scavenged hydroxyl radical, with an efficiency which increased in the order: tyrosol < hydroxytyrosol < oleuropein < caffeic acid. Polar substituents at the para position, such as in caffeic acid and oleuropein, were correlated with higher hydroxyl radical quenching ability.     

Applications of protecting groups in the synthesis of surfactants, lipids, and related compounds

Several types of alkyl ether lipids were prepared in high yield and high purity using protecting groups such as 1,3-dioxolane compounds or allyl ethers. We also succeeded in the industrial production of alkyl glyceryl ethers using the reaction of alkyl glycidyl ethers with acetone to give 1,3-dioxolane compounds, from which the desired alkyl glyceryl ethers were obtained in high quantities. 1,3-Dioxolane (ketal) compounds based on acetone were used in the enzymatic preparation of monoglyceride on an industrial scale. On the basis of these protecting groups, we extended our studies concerning both the preparations and properties of novel polyol ether compounds, beginning with alkyl glycidyl ethers. Another typical property of surfactants containing 1,3-dioxolane units and acetal is degradability under acidic conditions. Several types of destructible/cleavable surfactants based on polyols, such as carbohydrates and polyethyleneglycol, were prepared. As for natural products containing polyol skeletons, much attention has been paid to their molecular design, in which protecting groups such as 1,3-dioxolane compounds or allyl ether have contributed to synthetic strategies.     

催化臭氧化处理酚类化合物的研究进展与机理解析

催化臭氧化技术具有操作简单、氧化效率高、二次污染小等特点,在水中酚类化合物的去除方面具有较大的技术优势。本文以酚类化合物的催化臭氧化处理为切入点,介绍了均相催化臭氧化（二价铁离子）和非均相催化臭氧化（金属型、硅基负载型、碳基负载型、铝基负载型）处理不同浓度梯度酚类化合物的研究进展。然后,基于上述研究进展,根据污染物氧化过程的探针实验结果、催化剂表征特性和有机物转化规律,阐述了苯酚等酚类化合物的催化臭氧化机理。最后,从新型催化剂的再开发、酚类化合物的广谱催化和催化氧化机理的进一步探讨方面对催化臭氧化处理酚类化合物进行了展望。     

Acoustic emission and e.s.r. studies of polymers under stress

A nearly noise-free apparatus for the stressing of polymers is described. It has been used, in conjunction with a sensitive piezo-electric transducer and associated apparatus for the generation, detection and collection of acoustic emissions, from stressed polymers. It is shown that detectable levels of acoustic energy are released from several polymers and composites, and that the distribution of acoustic events varies with material examined. Parallel experiments have been carried out in which free radicals are generated by stressing bulk polymer in the cavity of an e.s.r. spectrometer. There is some correlation between stress and both acoustic emissions and free radical generation.     

测氧法研究受阻酚抗氧剂的抗氧化活性及反应动力学

采用测氧法考察了4种市售受阻酚抗氧剂的抗氧化活性,同时对其清除ROO·反应进行了动力学分析。结果表明:4种受阻酚抗氧剂对ROO·均具有良好的清除作用,并且抗氧化活性随着酚羟基浓度增加而增大。在同等的酚羟基浓度下,抗氧剂的抑制速率常数kinh值从大到小的顺序为抗氧剂1098、抗氧剂BHT、抗氧剂1010、抗氧剂1076。抗氧剂的抗氧化活性与功能基团的个数和对位取代基的供电性密切相关,酚胺复合型抗氧剂体现出更高的抗氧化活性。     

菜芙蓉花体外抗氧化活性部位的研究

采用连续提取法对菜芙蓉花乙醇提取物进行分离,得到石油醚相、乙酸乙酯相、正丁醇相和萃余水溶物4个不同极性部位。以还原力和清除羟自由基(·OH)、超氧阴离子自由基(O_2~-·)、DPPH自由基(DPPH·)能力为评价指标筛选其活性部位,并对活性最强部位进行体外小鼠红细胞溶血、肝组织匀浆和肝线粒体丙二醛(malondialdehyde,MDA)生成量及其肿胀度的研究。结果表明:菜芙蓉花提取物不同极性部位对自由基的清除能力表现为DPPH·O_2~-··OH,其中乙酸乙酯部位(Ethyl acetate Extract,EA)对三者清除能力最强,半清除浓度EC50分别为3.52、44.96、376.87μg/m L。在体外脂质过氧化抑制作用研究中,EA能够显著抑制小鼠红细胞溶血(p0.05),在50~500μg/m L范围内能抑制肝组织匀浆和肝线粒体MDA的生成,并有效抑制小鼠肝线粒体的肿胀,具有量效关系。     

虎杖中抗氧化成分的提取分离及其活性研究

提取了虎杖中具有抗氧化活性的总蒽醌(TA),并从总蒽醌中依次分离出强酸成分(SAP)、中酸成分(MAP)和弱酸成分(WAP)。然后采用二苯代苦味酰自由基(DPPH)法对不同质量浓度的TA、SAP、MAP和WAP进行了抗氧化活性测定。TA、SAP、MAP和WAP质量浓度分别为0.2 g/L、0.5 g/L、0.8 g/L、1.2 g/L时,对自由基的最大清除率依次分别为:29.5%、67.1%、85.7%、87.5%;34.0%、74.2%、86.5%、95.4%;9.8%、24.0%、35.2%、47.3%;6.5%、11.1%、19.6%、19.9%。TA、SAP、MAP和WAP对自由基均有程度不同的清除作用,其中SAP的效果最佳,当其质量浓度为1.2 g/L时,最大清除率可高达95.4%。     

受阻酚类抗氧剂结构与其抗氧化性能的影响关系

选取了3种酚羟基个数不同的受阻酚类抗氧剂为研究对象,通过性能测试、氧化诱导温度测试以及羰基指数测试等对添加抗氧剂后合成的聚乙烯进行对比分析,考察抗氧剂结构对聚乙烯性能的影响。结果表明,虽然受阻酚类抗氧剂中酚羟基的个数增多可以提高抗氧剂的抗氧化效果,但耐老化性能变弱,因此优选适宜的酚羟基个数对于提升受阻酚类抗氧剂的抗氧化性能十分必要。