Effect of Storage Conditions and Antioxidants on the Oxidative Stability of Sunflower–Chia Oil Blends

The mixture of different proportions of sunflower with chia oil provides a simple method to prepare edible oils with a wide range of desired fatty acid compositions. Sunflower–chia (90:10 and 80:20 wt/wt) oil blends with the addition of rosemary (ROS), ascorbyl palmitate (AP) and their blends (AP:ROS) were formulated to evaluate the oxidative stability during storage at two temperature levels normally used, cool (4 ± 1 °C) and room temperature (20 ± 2 °C) for a period of 360 days. Peroxide values (PV) of the oil blends with antioxidants stored at 4 ± 1 °C showed levels ≤10.0 mequiv O₂/kg oil; the lowest levels of PV were found for blends with AP:ROS. Values higher than 10.0 mequiv O₂/kg were observed between 120–240 days for oil blends stored at 20 ± 2 °C. Similar trends were observed with p-anisidine and Totox values. The oxidative stability determined by the Rancimat method and differential scanning calorimetry showed a greater susceptibility of the oils to oxidative deterioration with increasing unsaturated fatty acids content. The addition of antioxidants increased the induction time and decreased the Arrhenius rate constant, indicating an improvement in the oxidative stability for all the oil blends. Temperature had a strong influence on the stability of these blends during storage.     

Antioxidant Activity Evaluation of Tocored through Chemical Assays,Evaluation in Stripped Corn Oil,and CAA Assay

γ‐Tocopherol‐5,6‐quinone (tocored) is a crucial oxidized product of γ‐tocopherol (γ‐T) found in edible oil. Previously published studies on antioxidant activity (AOA) of tocored are not consistent. This study aims to monitor its AOA comprehensively through chemical assays (1,1‐diphenyl‐2‐picrylhydrazyl [DPPH] and ferric reducing antioxidant power [FRAP]), antioxidant evaluation in a food model system (stripped corn oil), and cellular antioxidant activity (CAA) assay, which would reasonably widen the knowledge of the AOA of γ‐T and tocored. In both DPPH and FRAP assays, tocored shows less AOA than γ‐T. Results of chemical properties in the Schaal oven test show that tocored possesses better AOA than γ‐T. Correlation coefficients of γ‐T and tocored between peroxide and K₂₃₄ or p‐AnV are 0.8784–0.9875 and 0.8716–0.9879, respectively. The CAA assay also shows that tocored possesses better cellar AOA than γ‐T, with an EC₅₀ at 21.55 µg mL^?1. Drawing conclusions from the results from chemical assays, evaluation in stripped corn oil, and CAA assay, tocored is verified as a potent antioxidant in edible vegetable oils compared to γ‐T. Practical Applications: The present work widens the knowledge of antioxidant activity of tocored and gamma‐tocopherol, and contributes to the understanding of existing antioxidant activity when gamma tocopherol is depleted when edible oils are in storage and processing processes.     

Effects of free fatty acids on oxidative stability of vegetable oil

The effect of free fatty acid (FFA) content on the susceptibility to thermooxidative degeneration of vegetable oils was determined by Rancimat analysis. A prooxidant effect of FFA was observed in all filtered oils, independently of lipidic substrate and of its state of hydrolytic and oxidative alteration. The intensity of this effect was related to FFA concentration, but regression analysis of the experimental data did not show a general correlation law between FFA concentration and induction time (I _t). Different results were obtained for freshly processed virgin olive oils, characterized by postpressing natural suspension-dispersion: opposite behavior was observed of FFA content as regards oxidative stability, depending on the presence of suspended-dispersed material. This fact is of interest because the dispersed particles play a double stabilizing effect on both oxidative and hydrolytic degradation. These results showed that avoidance of oil filtration is highly desirable to extend olive oil’s shelf life.     

Antioxidant activity in soybean oil of extracts from thompson grape bagasse

The phenolic compounds of Thompson grape bagasse were extracted using a 95:5 (vol/vol) ethanol/water mixture. Measurement of the antioxidant activity in refined soybean oil of bagasse grape extract was performed by using two different methods, the Rancimat method and the Schaal oven method in conjunction with peroxide value determination. The antioxidant activity of the extract was compared to the tertiary butyl hydroquinone (TBHQ) and butylated hydroxyanisole (BHA) activity. The bagasse grape extract showed similar antioxidant activities in both methods employed. At all concentrations tested [0.1, 0.3 and 0.5% of total phenols (TP)] the extract exhibited appreciable activity, which exceeded the activity of BHA. At some concentrations (0.3 and 0.5% TP) the extract exhibited activity comparable to that of TBHQ. Bagasse is a byproduct with a high content of phenolic compounds and is a good source of natural antioxidants.     

Natural antioxidants produced in oxidized lipid/amino acid browning reactions

1-Substituted pyrroles (1 and2) and1-substituted 2-(1′-hydroxypropyl)pyrroles (3–5) were produced in reactions between a lipid peroxidation product, 4,5(E)-epoxy-2(E)-heptenal, and the amino acid lysine. The antioxidative activity of compounds1–5 was studied. Oxidative stability was evaluated in refined soybean oil containing compounds1–5, butylated hydroxytoluene (BHT),n-propyl gallate orl-lysine, at concentrations of 50–200 ppm. Oils were either oxidized at 60°C and oxidation products determined by the thiobarbituric acid-reactive substances assay, or they were oxidized at 110°C by the Rancimat method. Although both methods gave similar results, greater differences were observed at 60°C than at 110°C. Addition of compounds1–5,l-lysine, BHT, and propyl gallate significantly (P<0.01) protected the oil against oxidation. The effectiveness order found was:l-lysine << compounds3–4 < compounds1–2 < compound5 ≈ BHT << propyl gallate.     

Determination of oxidation stability of soybean oil with the oxidative stability instrument: Operation parameter effects

Operation parameters of the oil stability index instrument were evaluated to determine their effect on the oxidative stability of commercial soybean oil. A factorial design was developed to evaluate the following three parameters, each at two levels, sample weight (2.5 or 5.0 g), conductivity tube temperature (20 or 30°C), and air flow rate (12 or 20 L/h), for a total of eight observations. Significance testing indicated that sample size and air flow rate affected oil oxidative stability independently (P<0.001), but not in combination. The conductivity tube temperature did not affect the oxidation stability index. Presented at the 1993 American Oil Chemists’ Society Meeting in Anaheim, California.     

Influence of metal contaminants on oxidation stability of Jatropha biodiesel

According to proposed National Mission on biodiesel in India, we have undertaken studies on stability of biodiesel from tree borne non-edible oil seeds Jatropha. European biodiesel standard EN-14214 calls for determining oxidation stability at 110 °C with a minimum induction time of 6 h by the Rancimat method (EN-14112). Neat Jatropha biodiesel (JBD) exhibited oxidation stability of 3.95 h and research was conducted to investigate influence of presence of transition metals, likely to be present in the metallurgy of storage tanks and barrels, on oxidation stability of Jatropha methyl ester. It was found that influence of metal was detrimental to oxidation stability and catalytic. Even small concentrations of metal contaminants showed nearly same influence on oxidation stability as large amounts. Copper showed strongest detrimental and catalytic effect. The dependence of the oxidation stability on the type of metal showed that long-term storage tests in different types of metal containers for examining the influence of container material on oxidation stability of biodiesel may be replaced by significantly faster Rancimat test serving as an accelerated storage test.     

Enhancing the oxidation stability of Mahua oil methyl ester with the addition of natural antioxidants

A rapid decrease in the availability of non-renewable fossil fuels has initiated the search for alternative fuels. Biodiesel obtained from various feedstocks has proved to be an effective alternative source for diesel engines due to its convincing fuel characteristics. The oxidation property of biodiesel is influenced by external factors such as sunlight and exposure to atmosphere.The oxidation stability of biodiesel can be improved by the addition of antioxidants which may be synthetic or natural. Natural antioxidants are more effective than synthetic ones in terms of economic value as well as prevention of adverse carcinogenic effects. Natural antioxidants, namely, ginger, Moringa oleifera, oregano, basil, and clove were extracted and used for the present study. The antioxidant activity of the additives was analyzed by DPPH (2, 2-diphenyl-1-picrylhydrazyl) radical scavenging activity. The DPPH scavenging effect was calculated in terms of % by using absorbance values recorded with UV spectrophotometer. Among the antioxidants used, clove additive was found to be more efficient in enhancing the oxidation stability, with scavenging effect of 42.23%, 47.67%, 51.62%, and 55.61% for 500, 1000, 1500, and 2000 ppm, respectively. It was also observed that the scavenging activity increased with the concentration of antioxidant additives, and the maximum value was recorded at a concentration of 2000 ppm. Mahua oil methyl ester (MOME) was selected as biodiesel for the present study for which the oxidation stability has to be evaluated. The oxidation stability of MOME was measured in terms of induction period using the Rancimat method which does not meet the required standards. The oxidation stability of MOME, MOME + ginger 2000, MOME + M. oleifera 2000, MOME + oregano 2000, MOME + basil 2000, and MOME + clove 2000 was evaluated. The highest induction period was observed to be 38.44 h for MOME + clove 2000 blend. Hence, clove additive was found to be more effective among the selected natural antioxidants in terms of increasing the scavenging effect as well as increasing the oxidation stability of MOME. Thus, the addition of natural antioxidants can be recommended to improve the oxidation stability of biodiesel based on their scavenging effect which can be further validated by means of the Rancimat method in terms of the induction period