Induction Period Of Oxidation Research Articles

An accessible method for the evaluation of the thermo-oxidative stability of organic substrates based on vegetable oils

A novel cost-effective computerized method is proposed for the determination of the oxidation induction period (OIP) of organic substrates. All component parts of the device are factory-made (interchangeable) details, which are widely used in laboratory practice. A sample is charged into the reactor, the closed reactor-condenser-stopcock system is evacuated. Then the device is filled with oxygen. The reactor is warmed up to balance with atmospheric pressure. The device is sealed and stirring of the heating medium, substrate and digital data transfer from the pressure sensor to the computer is started. The monitoring of the autooxidation of the sample is terminated after the system pressure has decreased by 300hPa. A test report is formed with the aid of a computer using Microsoft Excel; OIP is determined as the point of intersection of two tangent lines to the curve. The proposed method is on a par with standardized methods in terms of the repeatability of measurement results.

Migration Characteristics and Degradation Kinetics of Bisphenol A

This paper study the migration characteristics and degradation kinetics of bisphenol A using TGA - gas chromatography - mass spectrometry and found that bisphenol A polycarbonate in the thermal oxidative aging conditions of 130 °C de-gradated to bisphenol A. At the range of 0 h to 120 h, the bisphenol A content of environmental hormones increased with time. When it reached 120 h, bisphenol A environmental hormone content decreased slightly with aging time. The content of bisphenol A reached 495mg/kg when the thermal oxidative aging time was 168 h, which was decreased compared to the content of 442mg/kg at 120 h. Polycarbonate thermal decomposition kinetics study showed that the thermal decomposition of polycarbonate can be divided into three phases. The first thermal decomposition occurred at the range of 415° C to 425 ° C, the polycarbonate end groups fracture of the second stage at 493.6°C , the main fracture of the main chain rearrangement and crosslinking, and the third stage at 598.7°C, the degradation of the chain continues to decompose and the decomposition of the crosslinked carbon precursor; thermal oxidation aging of polycarbonate decreased the heat stability and promote the thermal decomposition of polycarbonate. Comparing the oxidation induction period, thermal weight loss rate and activation energy of polycarbonate before and after thermal oxidative aging, it c found that the thermal stability of the hot oxygen aging of polycarbonate is reduced.

Investigation of Using Beijing Grass Extract as a Natural Antioxidant in Edible Oil

Beijing grass [ Murdannia loriformis (Hassk) Rolla Rao et Kammathy] has been widely used as a Thai medicinal plant. In this study, the antioxidant activity of the ethanolic extract of Beijing grass was evaluated using the DPPH assay. Furthermore, the extract was added into soybean oil and pork lard, which were incubated at 75°C for 14 days. Peroxide value and color of the oil were determined during the storage in order to screen suitability of the extract as a natural antioxidant in edible oil. The antioxidant activity of the Beijing grass extract at 200, 400, 600 and 800 ppm were 60.38, 70.13, 85.38 and 87.29%, respectively according to the DPPH assay. Protection factor was calculated to show a relative increase of the induction period of lipid oxidation due to the addition of antioxidant. The protection factors of the Beijing grass extract in pork lard at 200, 400, 600 and 800 ppm were 1.4, 1.6, 1.6, and 1.6, respectively. This suggested that the extract helped increase oxidative stability of the oil compared to the control without antioxidant. However, antioxidant efficiency of the Beijing grass extract was relatively low compared to synthetic antioxidant BHT which possessed the protection factor of 3.3. The same trend was observed in soybean oil in the way that Beijing grass extract at 200, 400, 600 and 800 ppm showed protection factor of 1.2, 1.2, 1.2, and 1.3, respectively. TBHQ, a synthetic antioxidant, again exhibited significantly higher antioxidant activity compared to the Beijing extract in soybean oil. Measuring the Hunter L , a , b values of the oil suggested that the Beijing extract caused the oil lightness to decrease, while the greenness and blueness increased. In conclusion, the Beijing grass extract showed great potential as an effective natural antioxidant to protect edible oil from lipid oxidation. However, the impact of the extract on the color of the oil is still a great concern that needs to be further investigated.

Effects of extraction processes on the antioxidant activity of apple polyphenols

The effects of microwave-assisted extraction, ultrasound-assisted extraction and water bath extraction on the antioxidant activity of apple polyphenols are reported in this short communication. This study evaluated these methods based on their effect on the antioxidant activity of apple polyphenols whereas previous studies focused only on the yield rate of the extraction methods. The oxidation induction periods of apple polyphenols were 6.11, 3.26 and 1.13 h for microwave-assisted extraction, ultrasound-assisted extraction and water bath extraction, respectively. This result indicates that from the perspective of antioxidant activity protection microwave-assisted extraction is much better than the other two methods. Hopefully, this study could attract researchers’ attention to the property of apple polyphenols in extraction and promote the development of natural polyphenols extraction methods.

Characterization of Vanaspati Fat Produced in Iran

AbstractVanaspati is the main culinary fat consumed in Iran. It is produced from vegetable oils using different modification processes such as hydrogenation, fractionation, interesterification or blending. To characterize this product, samples from different Iranian brands were collected and their physicochemical properties were studied. Iranian vanaspati contains 0.3–6.2 % trans fatty acids and 24.8–30.5 % saturated fatty acids. Linoleic acid with a range of 32.5–40.3 % is the main unsaturated fatty acid of vanaspati. Iodine values and saponification values of the samples were in the range of 91.9–106.4 and 193.2–194.3, respectively. Free fatty acid contents between 0.04 and 0.10 % and peroxide values between 2.0 and 8.8 mequiv/kg were detected in samples. The induction period of oxidation of the samples was found to be between 8.5 and 15.4 h at 110 °C. With an average slip melting point of 32.9 °C, samples contained 10.0–22.6 % solid fat content at 10 °C, 4.2–10.6 % at 20 °C, 0.3–5.2 % at 30 °C and 0.0–0.5 % at 40 °C. The induction period of crystallization and crystallization rate of samples, were in the range of 0.0–33.11 min and 0.07–2.54 1/min, respectively. Lovibond red and yellow color indices of the product were found to be in the range of 5.0–7.3 and 69.5–70.2, respectively.

Effect of oxidation and modifiers on polypropylene crystallization

The effect of ester modifiers [di-n-alkyl esters derived from o-phthalic acid and C7-C9 alcohol fractions; poly(propylene glycol adipate) dibutyl ester] on the polypropylene oxidation and crystallization was studied. The modifiers influence the size of the crystallization nuclei and the polypropylene crystallization rate. Various models were used for mathematical description of the process, of which the Avrami model appeared to be the most adequate. The ester modifiers strongly influence the resistance of polypropylene to thermal oxidation: introduction of poly(propylene glycol adipate) dibutyl ester, thermodynamically incompatible with polypropylene, leads to a considerable increase in the induction period of oxidation.

Effects of supported metallocene catalyst active center multiplicity on antioxidant-stabilized ethylene homo- and copolymers

A silica-supported bis(n-butylcyclopentadienyl) zirconium dichloride [( n BuCp)2ZrCl2] catalyst was synthesized. This was used to prepare an ethylene homopolymer and an ethylene–1-hexene copolymer. The active center multiplicity of this catalyst was modeled by deconvoluting the copolymer molecular mass distribution and chemical composition distribution. Five different active site types were predicted, which matched the successive self-nucleation and annealing temperature peaks. The thermo-oxidative melt stability, with and without Irganox 1010 and Irgafos 168, of the above polyethylenes was investigated using nonisothermal differential scanning calorimetric (DSC) experiments at 150 °C. This is a temperature that ensures complete melting of the samples and avoids the diffusivity of oxygen to interfere into polyethylene crystallinity and its thermo-oxidative melt degradation. The oxidation parameters such as onset oxidation temperature, induction period, protection factor, and S-factor were determined by combining theoretical modeling with the DSC experiments. Subsequently, these findings were discussed considering catalyst active center multiplicity and polymer microstructure, particularly average ethylene sequence length. Several insightful results, which have not been reported earlier in the literature, were obtained. The antioxidant effect, for each polymer, varied as (Irganox + Irgafos) ≈ Irganox > Irgafos > Neat polymer. The as-synthesized homopolymer turned out to be almost twice as stable as the corresponding copolymer. The antioxidant(s) in the copolymer showed higher antioxidant effectiveness (AEX) than those in the homopolymer. Irganox exhibited more AEX than Irgafos. To the best of our knowledge, such findings have not been reported earlier in the literature. However, mixed with Irganox or Irgafos, their melt oxidation stability was comparable. The homopolymer, as per the calculated S-factor, showed Irganox–Irgafos synergistic effect five times that of the copolymer. This illustrates how the transition in backbone structure, from exceedingly high to low ethylene sequence length, influences antioxidant synergistic performance. Finally, this study shows a DSC-aided approach that can elucidate the effect of polyethylene structural backbone on its thermo-oxidative melt degradation as well as antioxidant synergism in a facile fashion.

Re-addition of antioxidant to aged MEROX and hydroprocessed jet fuels

Long term storage of aviation turbine fuels often requires the use of antioxidants with many military fuel specifications mandating its addition for hydroprocessed fuels. This work examines the influence of antioxidants on aged and freshly refined aviation turbine fuels of various types, some containing antioxidant at manufacture and others not. The rate of antioxidant depletion is reported along with the re-stabilised fuel’s oxidation induction periods. It was found that some fuel types do not benefit from re-addition of antioxidant and no improvement was observed for inhibition of hydroperoxide formation in aged fuels, however oxidation induction times were improved for re-addition of antioxidant for all fuels examined. A simple method for assessing the degree of hydroprocessing of an unknown fuel was also examined with limited success.

Effects of temperature and pressure level on lipid oxidation and physicochemical properties during chafing dish fried process (606.1)

Chafing Dish is very important and common condiment for Chinese customers. The effects of different temperatures and pressure levels on Acid value, TBARS and physicochemical properties of the chafing dish products were investigated during fried process. The chemical parameters, such as Acid Value, TBARS, NaNO3 and NaNO2, slightly increased as temperature, but Aw decreased from 0.45 to 0.38 when temperature was increased from 80 °C to 160 °C. In addition, L* value (66.05) at 100 °C were highest in all of groups, while the lowest of a* value (18.66) was observed at 160 °C. For the chemical parameters of the chafing dish products, they slightly increased as pressure except for Aw. For 400 MPa, chemical parameters were significantly different (p < 0.05) from other treated samples. Of importance, the lower pressure restrained the increase of NaNO3 and NaNO2 which were harmful for health. At 100 MPa, the treatment increased significantly the L* and a* value. However, the higher pressure (>100Mpa) decreased the L* and a* value of samples. Moreover, compared with temperature and pressure individually, combination of temperature and pressure effectively (p < 0.05) prolong the oxidation induction period of samples. Therefore, the study suggests that the lipid oxidation and physicochemical properties of chafing dish product can be regulated effectively by combination of temperature and pressure.Grant Funding Source: This research was supported by Application and Development Plan of CQ CSTC (No. CSTC2014yykfA0094)

Effects of various emulsification methods on the oxidation of methyl linoleate.

The effects of mechanical stress during emulsification on the oxidation of methyl linoleate were investigated by four methods (high-pressure homogenization, high-speed stirring, ultrasonic homogenization, and membrane emulsification). The oxidation rates and induction periods were almost constant, regardless of the emulsification method, except for membrane emulsification, by which the induction period was prolonged when a cellulose acetate membrane was used.

Effect of Natural Antioxidants, Irradiation, and Cooking on Lipid Oxidation in Refrigerated, Salted Ground Beef Patties

Antioxidant effects of natural antioxidants in 73%-lean ground beef patties during refrigeration were studied. Samples were subject to an antioxidant treatment (pomegranate extract, grape seed extract, butylated hydroxyanisole, or no treatment) and an irradiation treatment (0 or 1.5 kGy) before being evaluated for both uncooked and cooked indicators of lipid oxidation. Chemical evaluation of antioxidant activity were determined over 9 d through measurement of thiobarbituric reactive substances values. Physical evaluation of antioxidant activity was monitored by changes in physical color and sensory odor analysis on patties before and after cooking. Butylated hydroxyanisole extended the induction period of oxidation in all unirradiated beef patties better than the natural antioxidants. Panelists were able to distinguish a difference (in terms of oxidation attributes) between patty samples of different antioxidant and irradiation treatments while samples were uncooked, but unable to distinguish a difference between patties after cooking.

Low density polyethylene – Chitosan composites

With the aim of develop new materials for active food packaging, composites of low-density polyethylene (LDPE) with chitosan (CS) or chitosan sodium montmorillonite clay nanocomposites (CSnano), with or without Irganox 1076 commercial synthetic antioxidant or vitamin E (VE) as natural antioxidant were prepared by melt processing. The obtained materials have been characterized by processing behavior, mechanical and thermal properties, positive groups determination, atomic force microscopy and standard tests to assess antimicrobial and antioxidant activities. The compositions assuring insignificant decrease in mechanical and thermal properties were selected as LDPE/3CSnano/VE and LDPE/6CSnano/VE. It has been shown the chitosan imparts antimicrobial properties to LDPE films while the vitamin E increased the oxidation induction period, especially for materials containing chitosan nanocomposites. The incorporation of both chitosan nanocomposites and vitamin E in polyethylene gave films with good antimicrobial and thermal properties because of significant increase of charge surface and important changes in surface topology and antimicrobial activity because of a synergistic effect. The nanocomposites cannot only passively protect the food against environmental factors, but they may enhance shelf life of food products.

Sensitive luminescence techniques to study the early stages of polymer oxidation

This paper describes recent developments in the use of chemiluminescence (CL) and profluorescent nitroxides (PFNs) in probing the “induction period” of polymer oxidation. CL measures the instantaneous rate of reaction of hydroperoxides responsible for initiating degradation and the spreading of oxidation, while PFNs can be used to measure the concentration of alkyl radicals produced in oxidation events and thus provide an integrating sensor for the extent of cumulative damage. The PFN additive acts as an oxidation retarder by competing with oxygen to scavenge the alkyl radicals that generate chain carrying peroxy radicals and so mirrors the performance of hindered amine stabilisers (HAS) in one part of their stabilisation cycle. Using the example of polypropylene (PP) and cis-polyisoprene (PIP) as substrates which can rapidly spread oxidative damage, the factors controlling the reaction of PFNs can be determined from CL and fluorescence as well as infra-red (IR) spectroscopy through the detection of oxidation products as measured by the carbonyl index. Matrix effects on the reactivity are demonstrated using a polyethylene-norbornene copolymer (TOPAS) as carrier for both PIP and the PFN and it is seen that the PFN is a radical scavenger only above Tg of the carrier. When PIP alone is oxidized, the PFN is an integrating sensor for free radical production under ambient conditions for up to twelve months while also stabilizing the polymer. Critically, it is thus able to determine the underlying rate of radical production in the oxidation induction period.

Preparation of polyaniline in the presence of polymeric sulfonic acids mixtures: the role of intermolecular interactions between polyacids

AbstractPolyaniline (PANI) was synthesized by chemical oxidation of aniline in the presence of mixtures of water-soluble poly(sulfonic acids) of different nature. Under these conditions, the use of polyacid templates leads to the formation of interpolymer complexes of PANI and polyacid mixtures. The obtained PANI complexes were characterized by UV, visible, near IR, and Fourier transform infrared spectroscopy. It was shown that the rigidity of the polyacid backbone and the composition of a polyacid mixture affect the electronic structure of PANI complexes and the duration of the induction period of aniline oxidation. Domination of the more rigid-backbone template in the synthesis of PANI complexes with mixtures of the rigid- and flexible-backbone polyacids was observed. According to the viscometry and FTIR spectroscopic data, the reason of the domination is the existence of the intermolecular interaction between the polyacids in the mixture. In this case, duration of the induction period of aniline oxidation was between these values for pure polyacids.

Performance of a phenolic antioxidant introduced by different procedures into polyethylene containing dispersed fillers

The performance of Irganox 1010 phenolic antioxidant was studied in relation to the procedure of its introduction into a stock of the polymer and dispersed filler powders. Three procedures were used for introducing the antioxidant: the antioxidant was deposited onto the surface of filler (procedure I) or polymer powder (procedure II) particles prior to mixing the components, or it was deposited after mixing the polymer and filler powders (procedure III). We studied mixtures with an inert filler (aluminum oxide) and with fillers active in polymer oxidation and regeneration of the phenolic antioxidant (dispersed zinc, zinc oxide). The film samples for the studies were prepared from powder stocks by hot pressing. The antioxidant performance was evaluated by the induction period of oxidation, which was determined from the time dependences of accumulation of carbonyl groups in the polymer structure.

Antioxidant Effects of Sesamol Released from Polymeric Films on Lipid Oxidation in Linoleic Acid and Oat Cereal

The antioxidant effects of sesamol films were evaluated using a food simulant (linoleic acid) and a real food (oat cereal). Sesamol was melt blended with high density polyethylene, linear low density polyethylene and ethylene‐vinyl acetate resins using co‐extrusion to produce sesamol films of multilayer structure; for comparison, films containing butylated hydroxytoluene (BHT) or no additive (as control) were also produced. At least 60% of the initial amount of sesamol remained in the films after extrusion. The release of sesamol from the sesamol films was about six times faster at 30°C than at 10°C. The antioxidant effectiveness of sesamol and BHT was evaluated on the basis of induction period of lipid oxidation, conjugated dienes (for linoleic acid), hexanal (for oat breakfast) and sensory evaluation. Compared with the control film, the sesamol films extended the induction period of linoleic acid by five and eight times at 40°C and 23°C, respectively. After 12 month storage at 23°C, hexanal formation was 59% less in cereal packaged with sesamol films than that packaged with control film. Rancid odours were detected in cereal packaged with control films, but not with sesamol or BHT films. The incorporation of sesamol had only slight effects on tensile properties and transparency. Copyright © 2012 John Wiley & Sons, Ltd.

Target release rate of antioxidants to extend induction period of lipid oxidation

Evidence from literature has shown that compared with instant addition, slow release of antioxidants has some advantages to inhibit lipid oxidation and extend shelf life of food products. In this paper, the hypothesis that there is a range of release rates of antioxidants which could provide the maximum extension of induction period for lipid oxidation was tested in a model system using a syringe pump to deliver tocopherol into linoleic acid. Conjugated dienes, the first products appearing in lipid oxidation, were measured to determine the length of induction period for onset of lipid oxidation during incubation at 30 and 40°C. Maximum inhibition of oxidation occurred at the release rates of 3.3×10−4 and 7.7×10−4g/day at 30 and 40°C, respectively, supporting the hypothesis. Based on the results, a term “target release rate” was defined and its application in controlled release packaging was discussed.

Characteristics of Oxidative Storage Stability of Canola Fatty Acid Methyl Ester Stabilised with Antioxidants

The storage effects on the oxidation characteristics of fatty acid methyl ester of canola oil (CME) were investigated in this study.CME stabilised with two antioxidants, i.e.2,6-di-tert-bytyl-p-cresol (BHT) and 6,6-di-tert-butyl- 2, 2'-methylendi-p-cresol (BPH), was stored at 20, 40 and 60°C.The oxidation stability data were measured by the Rancimat test method and it was found that both BHT and BPH addition increased the oxidation resistance of the CME. The results showed that when BPH or BHT was added at a concentration of 100 ppm, the oxidation induction period of the neat CME samples increased from 5.53 h to 6.93 hand 6.14h, respectively. Comparing both antioxidants, BPH proved to be more effective in increasing the oxidation resistance when both antioxidants were added at the same concentration. Furthermore, the oxidation induction time decreased linearly with the storage time. It was shown that the oxidation occurred rapidly in the first 8 weeks of storage. Later, a kinetic study was undertaken and first-order kinetics were applied to explain the oxidation characteristics of the CME added with antioxidants. This kinetic study focused on exploiting the activation energy values obtained from the Arrhenius equations. Also, the oxidation effects on other quality parameters, including acid value, peroxide value, kinematic viscosity, and water content, were examined.

Release property and antioxidant effectiveness of tocopherol-incorporated LDPE/PP blend films

Low-density polyethylene (LDPE)/polypropylene (PP) blend films in various blending ratios containing 3000 mg kg−1 of tocopherol were manufactured by an extrusion process. Tocopherol release properties were characterised and correlated with antioxidant effectiveness in retarding the oxidation of linoleic acid contacting the films at 40°C. The conditions without tocopherol (control) and with instant tocopherol addition corresponding to the amount included in the films were also prepared and compared with the film-contacting solutions. The effect of tocopherol inclusion and the blending ratio on their physical properties was also examined. A wide range of tocopherol diffusivity in 6.6 × 10−16–4.6 × 10−14 m2 s−1 were obtained by blend films. As PP content increases, the diffusivity decreased sharply at the beginning and levelled off later. The slower release of tocopherol in LDPE/PP blend films corresponding to lower tocopherol diffusivity retained the higher tocopherol concentration in the linoleic acid system providing better antioxidant effectiveness of the extended induction period in oxidation. The tocopherol inclusion reduced tensile strength and transparency significantly in an affordable range with higher tensile strength given by a higher PP ratio. LDPE/PP blending can be a useful tool to modulate the release profile of tocopherol and thus the antioxidant effectiveness of the tocopherol-incorporated antioxidant packaging film.

Antioxidative Capacity of the Degradation Products of Glucuronic and Galacturonic Acid from Subcritical Water Treatment

An aqueous solution of glucuronic or galacturonic acid was treated in a continuous tubular reactor under subcritical conditions. The antioxidative capacity of the degradation products was estimated by three assays. The DPPH radical-scavenging activity of the degradation products was measured. For both substrates, the DPPH radical-scavenging activity and substrate conversion increased with increasing residence time in the reactor. Glucuronic and galacturonic acid were treated in subcritical water and subsequently lyophilized. The lyophilized degradation products were investigated for their antioxidative activity against the oxidation of lioneic acid under accelerated conditions at 110 °C. The respective degradation products of glucuronic and galacturonic acid did not exhibit any antioxidative activity in linoleic acid, as reflected by the unaltered oxidation induction period. However, the lyophilized degradation products of the substrates effectively inhibited the oxidation of linoleic acid in aqueous dispersion initiated by the water-soluble initiator AAPH at 45 °C, by prolonging the oxidation induction period and decelerating the oxygen consumption rate in the propagation period.