Presence Of Phenolic Antioxidants Research Articles

Antifungal and Zearalenone Inhibitory Activity of Pediococcus pentosaceus Isolated from Dairy Products on Fusarium graminearum.

The present study was aimed to evaluate the bio-control efficacy of Pediococcus pentosaceus isolated from traditional fermented dairy products originated from India, against the growth and zearalenone (ZEA) production of Fusarium graminearum. The cell-free supernatants of P. pentosaceus (PPCS) were prepared and chemical profiling was carried out by GC-MS and MALDI-TOF analysis. Chemical profiling of PPCS evidenced that, the presence of phenolic antioxidants, which are responsible for the antifungal activity. Another hand, MALDI-TOF analysis also indicated the presence of antimicrobial peptides. To know the antioxidant potential of PPCS, DPPH free radical scavenging assay was carried out and IC50 value was determined as 32 ± 1.89 μL/mL. The antifungal activity of P. pentosaceus was determined by dual culture overlay technique and zone of inhibition was recorded as 47 ± 2.81%, and antifungal activity of PPCS on F. graminearum was determined by micro-well dilution and scanning electron microscopic techniques. The minimum inhibitory concentration (MIC) of PPCS was determined as 66 ± 2.18 μL/mL in the present study. Also a clear variation in the micromorphology of mycelia treated with MIC value of PPCS compared to untreated control was documented. Further, the mechanism of growth inhibition was revealed by ergosterol analysis and determination of reactive oxygen species (ROS) in PPCS treated samples. The effects of PPCS on mycelial biomass and ZEA production were observed in a dose-dependent manner. The mechanism behind the suppression of ZEA production was studied by reverse transcriptase qPCR analysis of ZEA metabolic pathway genes (PKS4 and PKS13), and results showed that there is a dose dependent down-regulation of target gene expression in PPCS treated samples. The results of the present study were collectively proved that, the antifungal and ZEA inhibitory activity of PPCS against F. graminearum and it may find a potential application in agriculture and food industry as a natural bio-controlling agent.

Study on propylene polymerization in the presence of phenolic antioxidant (Irganox 1076) and characterization of stabilized polymers

The aim of this study was to investigate different concentrations of Irganox 1076 on Ziegler–Natta catalyst performance during propylene polymerization. Antioxidant masking was conducted by addition of different molar ratio of triethylaluminum (TEAL). Proton nuclear magnetic resonance and Fourier transform infrared spectroscopy spectra confirmed the complete conversion of antioxidant to aluminum aryloxide form. The different concentrations of masked antioxidant with different molar ratio of TEAL were used during polymerization and the catalyst activity was evaluated. Morphology, particle size distribution, melt temperature, crystallization temperature, degree of crystallinity, oxidative induction time, and isotacticity of products in the presence of masked antioxidant were evaluated. Results showed that incomplete masking of OH phenolic antioxidant led to significant catalyst activity reduction. J. VINYL ADDIT. TECHNOL., 21:285–289, 2015. © 2014 Society of Plastics Engineers

Differentiation between phenol- and amino-substances in voltammetry determination of synthetic antioxidants in oils

Abstract The paper describes a method of voltammetric determination of antioxidants in lubricating oils developed with the use of Linear Sweep Voltammetry (LSV) and Fast Scan Differential Pulse Voltammetry (FSDPV). Experimental conditions have been found for simultaneous determination of phenol-based antioxidants and amino-antioxidants: the phenols can be electrochemically oxidized using the polarisation of gold disc electrode (AuDE) in the potential range of 0–1400 mV in 0.2 M H2SO4 in the presence of ethanol and acetonitrile at the ratio of 3:1. Secondary aromatic amines can be determined directly in this supporting electrolyte; the presence of phenolic antioxidants does not interfere with this analysis. On the other hand, secondary aromatic amines interfere with the determination of phenolic substances; therefore, the amines present have to be eliminated in a suitable way. A procedure for masking the aromatic amines using their reaction with nitrous acid has been suggested and optimised. The nitrosamines thus formed can be used for sensitive and selective determination of amino-antioxidants by means of cathodic reduction on the hanging mercury drop electrode (HMDE) using Fast Scan Differential Pulse Voltammetry. The method was applied in analysis of real samples of lubricating oils.

In-reactor stabilization of polypropene

Propene was polymerized with a high activity, high stereospecific supported Ziegler–Natta catalyst in presence of phenolic antioxidants (AO), phosphite processing stabilizers (PS) or sterically hindered amine stabilizers (HAS). PS and some HAS grades did not influence propene polymerization, but AO and most commercial HAS could interfere with the catalyst and reduce catalyst activity.

Horseradish peroxidase degrades lipid hydroperoxides and suppresses lipid peroxidation of polyunsaturated fatty acids in the presence of phenolic antioxidants

Linoleic acid hydroperoxide (LAOOH) was effectively degraded by horseradish peroxidase (HRP) in the presence of quercetin. Several natural phenolic antioxidants, such as quercetin, capsaicin, and alpha-tocopherol, acted as good hydrogen donors in the peroxidase reaction that occurs during lipid hydroperoxide degradation. However, glutathione, which is a non-phenolic antioxidant that acts as a hydrogen donor for glutathione peroxidase, could not suppress lipid peroxidation in the presence of HRP. Lipid hydroperoxides generated from eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were also degraded with HRP in the presence of quercetin, and oxidative decomposition of DHA was suppressed by this reaction.

Antioxidant activity of the extracts from Dillenia indica fruits

There has been growing interest in the beneficial health effects of consuming fruits and vegetables. Mainly, the presence of phenolic antioxidants is believed to have the protective mechanisms. In the present study the fruit of Dillenia indica was extracted with ethyl acetate, methanol and water. The total phenolic content of the extracts was determined by Folin–Ciocalteu method and antioxidant activity of the extracts was assayed through some in vitro models such as antioxidant capacity by phosphomolybdenum method, β-carotene-linoleate model system, and radical scavenging activity using α,α-diphenyl-β-picrylhydrazyl (DPPH) method. The total phenolic contents of the fruit extracts as tannic acid equivalents were found to be highest in methanol extract (34.1%) followed by ethyl acetate extract (9.3%) and water extract (1.4%). Antioxidant capacity of the extracts as equivalent to ascorbic acid (μmole/g of the extract) was in the order of methanol extract > ethyl acetate extract > water extract. In comparison with butylated hydroxyanisole (BHA), at 100 ppm of concentration, the antioxidant and free radical scavenging activities of the extracts assayed through β-carotene-linoleate model system, and DPPH method were also found to be highest with methanol extract followed by ethyl acetate and water extracts. The results indicated that the extent of antioxidant activity of the extract is in accordance with the amount of phenolics present in that extract and the fruit of D. indica is rich in phenolics may provide a good source of antioxidant.

Photooxidation of styrene–ethylene–butadiene–styrene (SEBS) block copolymer

The photooxidation of hydrogenated poly[styrene- b–butadiene- b–styrene] or poly[styrene- b–(ethylene–co-butylene)- b–styrene] (SEBS), has been studied using a variety of analytical and spectroscopic methods including yellowness, luminescence and FTIR spectroscopy coupled with crosslinking and hydroperoxide analysis in order to understand the nature of the processes involved. FTIR and luminescence analysis show complex oxidation processes with distinct features associated with each phase. Rates of photooxidation measured by carbonyl growth and discolouration show that low molecular weight samples are more photostable than those with high molecular weight. Oxidation primarily due to the aliphatic part occurs with a predominant absorption associated with terminal carboxylic acid groups at 1712 cm −1. Anhydrides, ketones, aldehydes, esters and α,β-unsaturated carbonyl species are also formed in this matrix. Unlike thermal oxidation there is no evidence for crosslinking. Thus, end group oxidation is a predominant process at the interphase boundary of the soft aliphatic and hard aromatic segments with the immediate autocatalytic formation of high concentrations of primary hydroperoxides during the early stages of oxidation. These species are unstable and breakdown rapidly leaving a steady-state concentration of more stable hydroperoxides. The luminescence confirms a rapid initial disruption of the polystyrene excimers coupled with the formation of long wavelength emitting polyconjugated chromophores, possibly, stilbene type in nature giving rise to weak colour formation. Phosphorescence analysis also indicated the presence of initial acetophenone chromophores, which are associated with polystyrene end-groups formed by chain breakage at the aliphatic links. These species can act as initial active sensitive sites for further breakdown, possibly via a thermally induced hydrogen atom abstraction process to give benzaldehyde and benzoic acid. These active end-groups show a typical autocatalytic growth and decay process. The end-chain aliphatic radicals then become the sites for initial rapid hydroperoxidation as well as attack of the butene-1 tertiary groups. The presence of phenolic antioxidants and phosphites appear to exhibit a synergistic effect in inhibiting the discolouration and oxidation processes. This is evident through thermal analysis (OIT) and luminescence. In the latter case the consumption of excimer is impaired by the presence of stabilisers while the initial acetophenone end-groups in SEBS are destroyed. This is in complete contrast to the effects observed in control unstabilised SEBS material. Mechanisms are proposed and discussed for each phase oxidation.

Thermolysis of polyethylene hydroperoxides in the melt 4. Effect of phenolic antioxidants and temperature on oxidation product formation

Phenolic antioxidants mostly lead to reduction of the oxidation product formation rate. This is similar to the effect of the phenols on the rate of thermolysis of polyethylene hydroperoxides in the melt. The most distinctive feature between the different products of hydroperoxide decomposition pertains to the maximum amount formed. For alcohol groups this maximum amount is lower in the presence of phenolic antioxidants than in their absence. For carbonyl groups it is the opposite. Formation of γ-lactones seems least affected by the presence of the antioxidants. Formation of trans-vinylene groups is most affected as the maximum amount formed is approximately doubled in the presence of phenolic antioxidants. Vinyl groups can be measured only in the presence of phenolic antioxidants. The effect of temperature on product formation has been determined mainly with the “initial linear” rates, the rates calculated according to the first-order rate equation showing too much scattering. The activation energy for alcohol group formation is practically the same in the absence and presence of phenolic antioxidants. It is comparable to the activation energy of pseudo-monomolecular hydroperoxide decomposition in polyethylene melts. The situation is different for carbonyl groups. In fact, the activation energy is depending heavily on the initial hydroperoxide concentration, much more than on the presence of phenolic antioxidants. It increases from 21 to 27 kcal/mol (88 to 113 kJ/mol) if polyethylene processing in air at 150 °C has been performed for 60 min instead of only 30 min. The activation energy for γ-lactone formation does not depend on the presence of phenols. For trans-vinylene groups, the activation energy seems to increase with the initial hydroperoxide concentration in the absence of phenols. This effect is much less pronounced in the presence of phenols. The most reliable value for the activation energy of vinyl group formation is close to 26 kcal/mol (109 kJ/mol).

Thermolysis of polyethylene hydroperoxides in the melt6. Mechanisms and formal kinetics of product formation in the presence of phenolic antioxidants

The presence of phenols does not affect the nature of thermolysis products. However, the relative amount of the various oxidation products can change significantly. These changes are important from a fundamental point of view. They lead to better understanding of the thermolysis mechanisms. The reduced yield of alcohol groups in the presence of phenols suggests transformation of part of the alkoxy radicals into products other than alcohols. It is attributed to disproportionation between macro-alkoxy and phenoxy radicals yielding a ketone and the original phenol. There is considerable increase of trans-vinylene group formation in the presence of phenols. The explanation is based on another disproportionation reaction involving macro-alkyl and phenoxy radicals to give a double bond and the original phenol molecule. The vinyl groups that can be measured in the presence of phenols are formed on intramolecular hydroperoxide decomposition. The reaction seems to proceed with the tertiary hydroperoxides formed in low-density polyethylene rather than with the normal secondary hydroperoxides. The formation of γ-lactones results from direct decomposition of α,γ-keto-hydroperoxides in 4-position to alcohol groups initially present and also from decomposition of such structures formed on thermolysis. These data allow for an estimation of intramolecular hydrogen abstraction by peroxy radicals in polyethylene. It is found that the last can reach close to 30%.

Thermolysis of polyethylene hydroperoxides in the melt: 1. Experimental kinetics of hydroperoxide decomposition

Polyethylene hydroperoxides have been generated in an open mixer at 150°C. Their thermolysis has been examined in the temperature range 150 to 200°C. The overall kinetics of decomposition could be easily explained by primary thermolysis reactions combined with auto-accelerated decomposition involving the alcohol groups resulting from hydroperoxide decomposition. However, these kinetics do not allow distinguishing between primary first-order and second-order decomposition. Both mechanisms yield the same good fit for the experimental data. The difficulties encountered with the integral approach showed the necessity for different attempts to thermolysis data analysis. The methods consisted in the determination of the rate constants through use of the data for the first stages only of hydroperoxide decomposition. One of these methods consisted in plotting the reciprocal polyethylene hydroperoxide concentration as a function of thermolysis time. Another method consisted in the determination of the first-order decomposition rate constant for the initial stages of hydroperoxide decomposition. These procedures allowed eliminating to a large extent the contribution from auto-accelerated hydroperoxide decomposition. Nonetheless, even with these precautions, the calculated first-order rate constant was increasing with the initial hydroperoxide concentration. Furthermore, a similar increase with the initial hydroperoxide concentration, although on a lower level, occurred if the experiments were carried out in the presence of phenolic antioxidants. This behavior is attributed to hydroperoxide decomposition induced by the free radicals arising from the primary hydroperoxide decomposition reaction. Linear extrapolation of the initial first-order rate constants to zero initial hydroperoxide concentration yields the true first-order rate constant for hydroperoxide thermolysis. The activation energy deduced from the variation of the extrapolated rate constants with temperature is close to 109 kJ mol −1. This value is much too small for monomolecular hydroperoxide decomposition. Hence, primary thermolysis of polyethylene hydroperoxides in the polymer melt is a pseudo-first-order reaction involving the interaction of the hydroperoxide group with a segment of the polymer. Although the data have been generated in the temperature range 150 to 200°C, the reaction is estimated to be dominant over true first-order decomposition up to 300°C. The rate constants for monomolecular decomposition of polyethylene hydroperoxide found in the literature are discussed.

Degradation and stabilisation of styrene–ethylene–butadiene–styrene (SEBS) block copolymer

The degradation of hydrogenated poly[styrene- b-butadiene- b-styrene] or poly[styrene- b-(ethylene-co-butylene)- b-styrene], (SEBS) has been studied using a variety of analytical and spectroscopic methods including thermal analysis, UV, luminescence and FTIR spectroscopy coupled with crosslinking and hydroperoxide analysis in order to understand the nature of the processes involved. High temperature oxidation of non-commercial unstabilised material results in chain scission and severe crosslinking giving rise to extensive discolouration. FTIR analysis shows complex degradation processes with distinct features associated with each phase. There is a solvent soluble clear phase showing oxidation due primarily to the aliphatic part with a predominant absorption associated with terminal carboxylic acid groups at 1713 cm −1. Anhydrides and α,β-unsaturated carbonyl species are also formed in this matrix. There is also a solvent insoluble phase, which is predominantly crosslinked aliphatic material due to the formation of hydroperoxides and peracids/peresters. Vinyl groups are also evident in this phase. Thus, end group oxidation is a predominant process with the immediate autocatalytic formation of high concentrations of primary hydroperoxides during the early stages of oxidation. These species are unstable and breakdown rapidly leaving a steady-state concentration of more stable hydroperoxides. The luminescence also shows a rapid initial disruption of the polystyrene excimers coupled with the formation of long wavelength emitting polyconjugated chromophores, possibly, stilbene type in nature. Colour is evident is both crosslinked and uncrosslinked phases. The former shows evidence for the presence of unsaturated carbonyl products and vinyl absorption. Phosphorescence analysis also indicated the presence of initial acetophenone chromophores, which are associated with polystyrene end groups formed by chain breakage at the aliphatic links. These species can act as initial active sensitive sites for further breakdown, possibly via a thermally induced hydrogen atom abstraction process. The end-chain aliphatic radicals are the sites for initial rapid hydroperoxidation. The presence of phenolic antioxidants and phosphites appear to exhibit a powerful effect in synergistically inhibiting the discolouration and oxidation processes. This is evident through thermal analysis (OIT) and luminescence. In the latter case the consumption of excimer is impaired by the presence of stabilisers while the initial acetophenone end-groups in SEBS are destroyed. This is in complete contrast to the effects observed in control unstabilised SEBS material. Mechanisms are proposed and discussed for each phase oxidation.

Degradation of ethylene-propylene copolymer in the presence of phenolic antioxidants

Degradation of ethylene-propylene copolymer in the presence of phenolic antioxidants

Role of indoles in the oxidative degradation of unstable diesel fuels. The ferric and cupric ion catalyzed oxidation of 1,2,3,4-tetrahydrocarbazole as a model compound study

Alkylindoles have been implicated in the formation of insolubles and color during ambient storage of diesel fuels containing light cycle oil. Oxidatively reactive diesel fuels are characterized by the inability of hindered phenol antioxidants to significantly suppress oxidative insoluble formation. Similarly, the Fe(acac) 3 and Cu(O 2 CC 9 H 17 ) 2 catalyzed oxidation of tetrahydrocarbazole (THC) occurs even in the presence of a high concentration of a hindered phenol antioxidant. A reasonable mechanism is proposed for the Cu 2+ catalyzed oxidation of THC in the presence of phenolic antioxidants. The significance of the proposed mechanism in enhancing our understanding of the chemistry involved in the oxidative degradation of unstable diesel fuels is discussed

Mechanisms and kinetics of photostabilization of polyolefins with N-methylated HALS

The present work concerns the mechanisms and kinetics of photostabilization with N-methyl HALS. It is found that the efficiency of this HALS type in polypropylene and polyethylene is often comparable to that of the corresponding unsubstituted HALS. This is attributed to very fast transformation of the N-methyl HALS into the formic acid salt of the corresponding NH-HALS. Such a transformation has been found previously and ascribed to free radical attack of the labile hydrogen atoms of the N-methyl group. Although free radical attack can account for corresponding findings on oven aging of polyethylene, it does not explain the findings on photooxidation of polyethylene. As a matter of fact, the rate of transformation of the N-methyl HALS is hardly affected by the presence of phenolic antioxidants. Furthermore, a benzoate-type UV stabilizer protecting mainly by free radical scavenging does not affect significantly the rate of transformation. To account for the effect observed with solid polyethylene, a photooxidative mechanism is envisaged. It is based on the formation of an exciplex oxygen-polymer. This exciplex is able to migrate in the polymer and is rather long lived. It is only when it involves a hydrogen atom that is sufficiently labile that there is reaction. The hydrogen atoms of the N-methyl group of HALS are reactive enough, so that reaction and transformation of the methyl group results, as found experimentally. Mechanism and kinetics of the reaction are discussed.

Effect of atomic oxygen on polymers

AbstractA stream of atomic oxygen, produced by passing oxygen at low pressure through a radio‐frequency coil, was allowed to impinge on films prepared from several dozen different polymers. The flow of oxygen radicals was regulated so that the reaction temperatures were between 40 and 70°C. The rapid reactions which occurred at the polymer film–oxygen radical interface were essentially unaffected by the presence of phenolic antioxidants over a wide range of concentrations but rate of reaction was greatly affected by the structure of the polymer. Bulk properties of the polymers were unchanged because the attack by atomic oxygen is limited to the surface of the polymer. In many instances a simple ablation of the surface was observed, but in some cases, especially polyethylene and polypropylene, a highly oxidized surface layer was created. These oxidized surface layers had remarkably low contact angles with water and should be of great interest in improving adhesion and other surface‐dependent properties of polymers.