On the kinetics of the autoxidation of fats. II. Monounsaturated substrates

The autoxidation of methyl oleate and oleic acid shows some differences as compared to the autoxidation of linoleate,e.g., the formation of water at an early stage. Linearization of experimental data on the autoxidation to high oxidation degrees of methyl oleate and other monounsaturated substrates shows that the rate equations previously derived for methyl linoleate in the range of 1–25% oxidation are valid, provided the correct expression for the remaining unreacted substrate is used. With monounsaturated substrates, part of the oxygen is consumed by a secondary oxidation reaction almost from the beginning, and only a certain constant fraction α of the total O₂ consumption is consumed in hydroperoxide formation. The fraction α is different for methyl oleate, oleyl alcohol, oleic acid andcis 9-octadecene, but the rate constant for the hydroperoxide formation is the same for all of them when experimental conditions are the same. The main difference between oleate and linoleate autoxidation is the much faster decomposition of the oleate hydroperoxides relative to their slow formation.     

Photodegradation and biodegradation by bacteria of mulching films based on ethylene‐vinyl acetate copolymer: Effect of pro‐oxidant additives

The photodegradation (432 h under irradiation of Xe‐Lamp‐solar filter) of an ethylene vinyl acetate (EVA) copolymer with vinyl acetate content of 9% was studied, and the effect of iron and calcium stearates was evaluated using different techniques such us attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR), gel permeation chromatography (GPC), and thermal analysis methods (DSC and TGA). A re‐arrangement in crystallization and consequent decrease in thermal stability were found through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), which were in agreement with the chain scission tendency. The presence of Ca and Fe pro‐oxidants additives in EVA films increased the ketone carbonyl formation and decreased the ester absorption band of the acetate respect to the pure EVA, as it was evidenced by the significant changes in Carbonyl Indexes found by FTIR. The activity of stearates has been also evaluated by chemiluminescence, where the temperature‐ramping tests under nitrogen showed the formation of a peroxide peak at lower temperature. The lower stability of the films containing pro‐oxidants was evidenced by the values of oxidation induction time (OIT) determined by DSC. The results were supported by GC‐MS, where the concentration of extracted products identified in the EVA containing pro‐oxidants was significant and a much greater decrease in molecular weight was determined by GPC, which confirmed the development of degradation for EVA with Ca and Fe stearates in comparison to pure EVA. Biodegradation of photodegraded EVA films were studied at 45°C during 90 days using a mixture of Bacillus (MIX) (B. cereus, B. megaterium, and B. subtilis) and, in parallel, by Brevibacillus borstelensis as reference strain. Biodegradation of EVA‐films was studied by Chemiluminescence, ATR‐FTIR and GC‐product analysis and the data confirm more efficient biodegradation on the materials containing pro‐oxidants. The chemiluminescence emissions due to decomposition of oxidation species was observed at lower temperatures on the biodegraded samples. Also, the drastic decrease of carbonyl index and the disappearance of photogenerated low molecular products with biodegradation were more efficient on the biodegraded films containing pro‐oxidants. EVA mineralization was evaluated by carbon dioxide measurement using indirect impedance technique. Biodegradation by B. borstelensis and MIX at 45°C was similar and exhibited a pronounced difference between the pure photodegraded EVA film (around 15% of mineralization) and the corresponding photodegraded films containing Ca and Fe stearates where biodegradation extent reached values of 23‐26% of biodegradation after 90 days. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Pro‐oxidant activity of Fe2+ in oxidation of cod phospholipids in liposomes

This work examines how different factors such as temperature, amount of injected Fe²⁺, lipid concentration, pH, concentration of NaCl and concentration of dissolved oxygen influenced the lipid oxidation rate of liposomes made from cod phospholipids. The rate of lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. The rate of oxygen consumption in liposomes was proportional to the concentration of iron and the lipid concentration in the assay mixture. The oxygen consumption rate was dependent on pH, with a maximum observed between pH 4 and 5. The addition of salt (final concentration 0.04–0.8 M) decreased the rate of oxygen consumption. The rate of oxidation was independent of the concentration of dissolved oxygen (in the range of 230–5 μM). The oxygen consumption rate followed Arrhenius kinetics, and the variation in activation energy found (60–87 kJ/moles×K) might be due to variations in the composition of raw materials used in the experiments and different susceptibility to oxidation.     

Effects of natural antioxidants on the lipid profile of electron beam‐irradiated beef burgers

The purpose of this study was to assess the efficacy of rosemary and oregano extracts in avoiding oxidative changes in beef burgers, and to evaluate the fatty acid profile of these products after electron beam exposition. Extracts, individually or in combination, were added to beef burgers and compared to synthetic antioxidants commonly used in food (butylated hydroxytoluene, butylated hydroxyanisole). The ground beef were submitted to electron beam irradiation at doses of 0, 3.5 and 7 kGy, and stored for 90 days. At regular time intervals, lipid oxidation and fatty acid composition were evaluated through measurement of thiobarbituric acid‐reactive substances (TBARS) and gas chromatography, respectively. The results indicate that, although the irradiation process triggers an increase in the lipid oxidation ratio expressed by TBARS values, great changes in the fatty acid profiles were not observed; instead, they continued to present characteristics very similar to that of non‐irradiated beef. Thus, as irradiation doses of up to 7 kGy for frozen meat can make foods safe from foodborne pathogens, natural antioxidants derived from spices are able to reduce and avoid lipid changes that may cause a deterioration of the sensory quality of these foods, and these natural extracts offer a good choice for replacing synthetic additives.     

Manganese stearate initiated photo‐oxidative and thermo‐oxidative degradation of LDPE,LLDPE and their blends

This study is an attempt to investigate the effect of a representative pro‐oxidant (manganese stearate) on the degradation behavior of 70 ± 5 μ thickness films of LDPE, LLDPE and their blends. Films were prepared by film blowing technique in the presence of varying quantities of manganese stearate (0.5–1% w/w) and subsequently subjected to accelerated degradative tests: xenon arc exposure and air‐oven exposure (at 70°C). The physico–chemical changes induced as a result of aging were followed by monitoring the mechanical properties (Tensile strength and Elongation at break), carbonyl index (CI), morphology (SEM), melt flow index (MFI), oxygen content (Elemental analysis), and DSC crystallinity. The results indicate that the degradative effect of pro‐oxidant is more pronounced in LDPE than LLDPE and blends, due to the presence of larger number of weak branches in the former. The degradation was also found to be proportional to the concentration of the pro‐oxidant. Flynn‐Wall‐Ozawa iso‐conversion technique was used to determine the kinetic parameters of degradation, which were used to determine the effect of the pro‐oxidant on the theoretical lifetime of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phenolic antioxidants – radical‐scavenging and chain‐breaking activity: A comparative study

Fifty phenolic antioxidants (AH) (42 individual compounds and 8 binary mixtures of two antioxidants) were chosen for a comparative analysis of their radical‐scavenging (H‐donating) and chain‐breaking (antioxidant) activity. Correlations between experimental (antiradical and antioxidant) and predictable (theoretical) activities of 15 flavonoids, 15 hydroxy cinnamic acid derivatives, 5 hydroxy chalcones, 4 dihydroxy coumarins and 3 standard antioxidants (butylated hydroxytoluene, hydroquinone, DL ‐α‐tocopherol) were summarized and discussed. The following models were applied to explain the structure‐activity relationships of phenolic antioxidants of natural origin: (a) model 1, a DPPH assay used for the determination of the radical‐scavenging capacity (AH + DPPH? → A? + DPPH‐H); (b) model 2, chemiluminescence of a model substrate RH (cumene or diphenylmethane) used for the determination of the rate constant of a reaction with model peroxyl radicals (AH + RO₂? → ROOH + A?); (c) model 3, lipid autoxidation used for the determination of the chain‐breaking antioxidant efficiency and reactivity (AH + LO₂? → LOOH + A?; A? + LH (+O₂) → AH + LO₂?); and (d) model 4, theoretical methods used for predicting the activity (predictable activity). The highest lipid oxidation stability was found for antioxidants with a catecholic structure and for their binary mixtures with DL ‐α‐tocopherol, as a result of synergism between them.     

The influence of antioxidants on the oxidation stability of biodiesel

Oxidation stability of bodiesel is an important issue because FA derivatives are more sensitive to oxidative degradation than mineral fuel. Therefore, in the most recent European Specifications for biodiesel, a minimum value of 6 h for the induction period at 110°C, measured with a Rancimat instrument, is specified. To guarantee this value at the filling station, the use of additional antioxidants will be necessary. In this paper we show the influence of different synthetic and natural antioxidants on the oxidation stability, using the specified test method. Biodiesel produced from rapeseed oil, sunflower oil, used frying oil, and beef tallow, both undistilled and distilled, was investigated. The four synthetic antioxidants pyrogallol (PY), propylgallate (PG), TBHQ, and BHA produced the greatest enhancement of the induction period. These four compounds and the widely used BHT were selected for further studies at concentrations from 100 to 1000 mg/kg. The induction periods of methyl esters from rapeseed, oil, used frying oil, and tallow could be improved significantly with PY, PG, and TBHQ, whereas BHT was not very effective. A good correlation was found between the improvement of the oxidation stability and the FA composition.     

3, 4‐Dihydroxymandelic acid amides of alkylamines as antioxidants for lipids

The antioxidative and radical scavenging activity of the 3, 4‐dihydroxymandelic acid (DHMA) amides of hexylamine, 2‐ethylhexylamine, octylamine, and cyclohexylamine was determined by several physicochemical test systems. The amides were synthesized by protecting group‐free coupling of in situ prepared N‐hydroxysuccinimidylester of DHMA and the amines. The radical scavenging activity was determined using the DPPH (2, 2‐diphenyl‐1‐picrylhydrazyl) method and by quenching superoxide anions generated using a horse radish peroxidase/H₂O₂ system. In the DPPH assay, all amides show higher radical scavenging activity (EC₅₀ 0.09‐0.12 mol/mol_DPPH) compared to the standard antioxidants ascorbic acid (EC₅₀ 0.27 mol/mol_DPPH) and tocopherol (EC₅₀ 0.25 mol/mol_DPPH). The amides are also more potent superoxide radical scavengers (IC₅₀ < 600 nm) than standard ascorbic acid (IC₅₀ 700 nm). Activity against lipid peroxidation was determined by accelerated autoxidation of highly unsaturated oils and squalene using the Rancimat. Again, the antioxidative potentials of the DHMA amides against lipid oxidation as determined by the Rancimat, are at least equal or higher compared to the standard lipid antioxidants tocopherol, BHT, BHA, and ascorbylpalmitate (concentration in soybean oil 0.05%, all other oils 0.025%, squalene 0.005%). In squalene, an equi‐amount mixture of DHMA octylamide and α‐tocopherol shows a synergistic effect. Last but not least, the amides are able to protect an emulsion of linoleic acid/β‐carotene against oxidation initiated by N, N‐azodiisobutyramidine dihydrochloride (IC₅₀ 0.19‐0.77 mmol/l, ascorbic acid > 0.9, tocopherol 0.08). The DHMA octylamide in combination with ascorbic acid shows a synergistic antioxidative effect in the emulsion model. In conclusion, the new alkylamides of DHMA are easy to synthesize, potent radical scavengers and protect lipids, in particular the highly unsaturated, both in bulk and in emulsions against autoxidation.     

Schiff base‐substituted polyphenol: synthesis,characterisation and non‐isothermal degradation kinetics

BACKGROUND: Polymers of phenols and aromatic amines have emerged as new materials in fields such as superconductors, coatings, laminates, photoresists and high‐temperature environments. The stability, kinetics and associated pollution of the thermal decomposition of oligophenols are of interest for the aforementioned fields. RESULTS: A new Schiff base polymer, derived from N,N′‐bis(2‐hydroxy‐3‐methoxyphenylmethylidene)‐2,6‐pyridinediamine, was prepared by oxidative polycondensation. Characterisations using Fourier transform infrared, UV‐visible, ¹H NMR and ¹³C NMR spectroscopy, thermogravimetric/differential thermal analysis, gel permeation chromatography, cyclic voltammetry and conductivity measurements were performed. The number‐average (M_n) and weight‐average molecular weight (M_w) and dispersity (D = M_w/M_n) of the polymer were found to be 61 000 and 94 200 g mol^?1 and 1.54, respectively. Apparent activation energies of the thermal decomposition of the polymer were determined using the Tang, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Coats–Redfern methods. The most likely decomposition process was a D_n deceleration type in terms of the Coats–Redfern and master plot results. CONCLUSION: The mechanism of the degradation process can be understood through the use of kinetic parameters obtained from various non‐isothermal methods. Copyright © 2009 Society of Chemical Industry     

Improving the aging resistance of styrene‐butadiene‐styrene tri‐block copolymer and application in polymer‐modified asphalt

Thermal oxidation process of styrene‐butadiene‐styrene (SBS) copolymer was studied by using a variety of analytical and spectroscopic methods including thermal analysis, dynamic mechanical analysis and FTIR spectroscopy. The experimental results indicate that the thermal oxidation process of SBS is a free radical self‐catalyzed reaction containing four steps (initiation, growth, transfer, and termination of the chain) with both crosslinking and scission and the latter is confirmed to be the main process. The antioxidants 1010 as scavenger of free radicals and 168 acting decomposition of hydroperoxides were used to improve the oxidation aging resistance of SBS copolymer. It has been found that synergic effect of 1010 and 168 may be the best in practice and 0.2 wt % 1010 + 0.4 wt % 168 can effectively prevent SBS from the thermal oxidation at certain temperature. Furthermore, the aging resistance of the SBS‐modified asphalt was improved by addition of complex antioxidants. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparative effects of cobalt carboxylates on the thermo‐oxidative degradation of LDPE films

This article reports the effect of three cobalt carboxylates—cobalt stearate (CoSt₃), cobalt palmitate (CoPal₃), and cobalt laurate (CoLau₃)—on the thermo‐oxidative degradation of low‐density polyethylene (LDPE) films prepared by sheeting process. The carboxylates were blended with LDPE in the concentration range of 0.05–0.2% (w/w). The degradation was monitored by techniques such as FTIR spectroscopy, change in the mechanical properties (tensile strength and elongation at break), viscometry, surface electron microscopy, melt flow index measurements, and apparent density measurements. Studies indicate that films containing these additives are highly susceptible to thermo‐oxidative degradation. Oxygen containing functionalities such as carbonyl and vinyl species are generated on the surface of polyethylene because of thermo‐oxidation, as indicated by FTIR studies. This oxidative process is accelerated in the presence of cobalt carboxylates. The degradation of LDPE was found to increase proportionally with concentration as well as with increasing chain length of the cobalt carboxylate, and follow the order CoSt₃ > CoPal₃ > CoLau₃. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3758–3765, 2007     

Enhancing Lipid Oxidative Stability of Cooked‐Chilled Lamb Meat through Dietary Rosemary Diterpenes

A dietary rosemary extract (DRE) containing carnosic acid and carnosol at 1:1 (w/w) for enhancing the lipid oxidative stability in cooked‐chilled lamb meat, is evaluated. Three diets for fattening lambs are tested: i) a cereal‐based concentrate (C‐diet); ii) the C‐diet plus 600 mg vitamin E per kg feed (E‐diet); and iii) the C‐diet plus 600 mg rosemary diterpenes per kg feed (R‐diet). Griddled‐chilled lamb patties are kept at 4 °C and lighting for 2 days, simulating catering conditions. Diterpenes have a lower deposition rate than vitamin E in lamb muscle and are completely degraded during cooking. DRE is thus less effective than dietary vitamin E in enhancing the oxidative stability of the patties. After 2‐day storage, the R‐diet shows lower (p < 0.01) peroxide values and thiobarbituric acid reactive substances than the C‐diet, while, in contrast to the E‐diet, it does not inhibit (p > 0.05) the formation of cholesterol oxidation products. The R‐diet increases (p < 0.05) the proportion of polyunsaturated fatty acids and decreases (p < 0.05) the n‐6/n‐3 ratio. These findings suggest antioxidant protection by dietary bioactive compounds beyond the direct radical scavenging activity that is able to stabilize lipids during the meat shelf‐life. Practical Applications: Cooked‐chilled meat lipids strongly oxidize in ready‐to‐eat dishes kept in retailing conditions, which may negatively affect their levels of polyunsaturated fatty acids (PUFA), cholesterol oxidation products (COP), and other lipid oxidation products. Dietary rosemary diterpenes can be used as a clean alternative to feed additives to enhance the oxidative stability of cooked‐chilled meat. Improved health and antioxidant status of the animal might be able to reduce oxidative spoilage during meat shelf‐life. Diterpenes provide lesser antioxidant protection than dietary vitamin E but may improve the PUFA content, with positive implications for the nutritional quality of lamb fat. The use of dietary antioxidants with different properties may contribute to improving the efficacy of animal feeds to improve meat quality.     

Fatty fish intake,n‐3 fatty acids and self‐rated health in middle‐aged adults

Background – Since n‐3 fatty acids, abundant in fatty fish, may improve health, we raised the question whether self‐reported intake frequency of fatty fish (FF) might be related to the percentage of n‐3 fatty acids in serum phospholipids (PL‐n‐3), and also to self‐rated health (H). Design – The study followed a cross‐sectional design. Methods – In the cross‐sectional Oslo Health Study, PL‐n‐3 were determined in 121 middle‐aged ethnic Norwegians and 102 immigrants from the Indian subcontinent and correlated with FF and H. Logistic regression was used to study the relationship between PL‐n‐3 and H (dichotomized, i.e. Poor vs. Good health). Results – FF correlated positively with PL20:5n‐3 (PL‐EPA, r = 0.467, p <0.001) and PL22:6n‐3 (PL‐DHA, r = 0.499, p <0.001), and negatively with PL20:4n‐6 (PL‐AA, r = –0.350, p = 0.001). H was positively associated with PL‐EPA (r = 0.321, p <0.001) and PL‐DHA (r = 0.275; p <0.001), but negatively with PL‐AA (r = –0.220, p = 0.001). The odds ratio for reporting Poor vs. Good health was significantly higher in subjects with low levels of PL‐EPA (OR = 1.49; 95% confidence interval = 1.17–1.89, p = 0.001), persisting after adjusting for sex, physical activity, ethnicity and length of education. Conclusion – The intake frequency of fatty fish is related to n‐3 fatty acids in the serum phospholipids, and to self‐rated health.     

Electropolymerization kinetics of o‐aminophenol and characterization of the obtained polymer films

Poly(ortho‐aminophenol) has been synthesized electrochemically from a previously deoxygenated acid medium. The initial rate of electropolymerization reaction on platinum electrode is small and the rate law is: Rate = k₂ [D]^0.50[HCl]^1.125[M]^1.29. The apparent activation energy (E_a) was found to be 68.63 kJ mol^?1. The polymer films obtained have been characterized by cyclic voltammetry, X‐ray diffraction, elemental analysis, TGA, scanning electron microscopy, ¹H NMR, UV–visible, and IR spectroscopy. The mechanism of the electrochemical polymerization reaction has been discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3093–3109, 2006     

A practical parametrical characterization of the Fenton and the photo‐Fenton sulfamethazine treatment using semi‐empirical modeling

BACKGROUND: Sulfamethazine (SMT) has received little attention in the water treatment literature. Yet, SMT is among the non‐biodegradable substances increasingly found in aqueous media and affecting both public health and wastewater treatments. For a long time, advanced oxidation processes (AOPs) were studied via pure empirical modeling, although the surface response models resulting from lumped information (TOC, COD, etc.) present limitations regarding extrapolation and optimization. Conversely, detailed first‐principles modeling may not be affordable due to the computational burden and the chemical analysis needs. Thus, a balanced approach may be practical in many cases. RESULTS: Experiments on SMT solutions (500 mL, 50 mg L^?1) were performed under conditions set by an experimental design. A set of replicated degradation time‐profiles (TOC and SMT concentrations) was obtained and a semi‐empirical kinetic model was fitted to these data to determine maximum conversion and kinetic rate. CONCLUSIONS: SMT can be completely degraded from water via photo‐Fenton treatment. Conditions for this treatment were investigated and its outcomes were systematically characterized by a simple kinetic model and two lumped parameters, conversion and kinetic rate. Both, the model and the corresponding parametrical characterization are introduced as a means to discriminate the most efficient treatment conditions in a practical and efficient way. Copyright © 2011 Society of Chemical Industry     

Partial oxidation of palm fatty acids over Ce‐ZrO2: Roles of catalyst surface area,lattice oxygen capacity and mobility

Nanoscale Ce‐ZrO₂, synthesized by cationic surfactant‐assisted method, has useful partial oxidation activity to convert palm fatty acid distillate (PFAD; containing C₁₆–C₁₈ compounds) to hydrogen‐rich gas with low carbon formation problem under moderate temperatures. At 1123 K with the inlet O/C ratio of 1.0, the main products from the reaction are H₂, CO, CO₂, and CH₄ with slight formations of gaseous high hydrocarbons (i.e., C₂H₄, C₂H₆, and C₃H₆), which could all be eliminated by applying higher O/C ratio (above 1.25) or higher temperature (1173 K). Compared with the microscale Ce‐ZrO₂ synthesized by conventional coprecipitation method, less H₂ production with relatively higher C₂H₄, C₂H₆, and C₃H₆ formations are generated from the reaction over microscale Ce‐ZrO₂. The better reaction performances of nanoscale Ce‐ZrO₂ are linearly correlated with its higher specific surface area as well as higher oxygen storage capacity and lattice oxygen mobility, according to the reduction/oxidation measurement and ¹⁸O/¹⁶O isotope exchange study. © 2010 American Institute of Chemical Engineers AIChE J, 2011