Natural and synthetic antioxidants: Influence on the oxidative stability of biodiesel synthesized from non-edible oil

According to the proposed National Mission on Biodiesel in India, we have undertaken studies on the oxidative stability of biodiesel synthesized from tree borne non-edible oil seeds jatropha. Neat jatropha biodiesel exhibited oxidation stability of 3.95 h and research was conducted to investigate the influence of natural and synthetic antioxidants on the oxidation stability of jatropha methyl ester. Antioxidants namely α-tocopherol, tert-butylated hydroxytoluene, tert-butylated phenol derivative, octylated butylated diphenyl amine, and tert-butylhydroxquinone were doped to improve the oxidation stability. It was found that both types of antioxidants showed beneficial effects in increasing the oxidation stability of jatropha methyl ester, but comparatively, the synthetic antioxidants were found to be more effective.     

Comparison of four accelerated stability methods for lard and tallow with and without antioxidants

The oxidative stability of lard and tallow with and without antioxidants was evaluated by four accelerated stability methods, the active oxygen method (AOM), the oxygen bomb test, the Rancimat method, and the Schaal oven test. The results indicated that the oxidative stability of animal fats and the relative effectiveness of an antioxidant in the fats could have different mechanisms. When the protective index was used to demonstrate the relative effectiveness of the antioxidants, the results suggested that the Rancimat Method may be the least reliable method compared with AOM, oxygen bomb test, and Schaal oven test. More than one accelerated stability method is recommended for evaluating the effectiveness of an antioxidant or the oxidative stability of fats.     

酸败仪法测定棕榈油炸方便面的氧化程度

对酸败仪法测定棕榈油炸方便面的氧化程度进行了实验研究,确定了测定的适宜条件,探讨了该法测定的准确度。研究发现采用酸败仪测定棕榈油炸方便面的氧化程度是可行的。     

Oxidative stability of purified common Kilka (Clupeonella cultiventris caspia) oil as a function of the bene kernel and hull oils

Oxidative stability of the purified common Kilka triacylglycerols (PKO) as affected by 1–8% w/w of bene kernel (BKO) and hull (BHO) oils was studied and compared with that of 100 mg kg^?1 of BHT and α‐tocopherol. Lipid oxidation was measured by monitoring peroxide value till the minute 80 (PV₈₀, meq kg^?1) and also by determining the oxidative stability index at 60 °C (OSI₆₀, h). In the Rancimat test, the OSI₆₀ of the PKO (1.66 h) was significantly increased by some of the added antioxidants, and the BKO 8% (7.98 h) had the highest antioxidant activity with no significant differences among the BHT, α‐tocopherol and the BHO 8%. Furthermore, an exponential regression curve with a good coefficient of determination (R² > 0.94) was observed between the changes in the PV₈₀ and OSI₆₀ values of the PKO.     

Cashew nut oil: effect of kernel grade and a microwave preheating extraction step on chemical composition,oxidative stability and bioactivity

The cashew nut kernels can be broadly classified by colour, size, quality and integrity, into whole (W), butts (B), splits (S) and P (pieces). This work evaluated seven sizes and qualities of cashew kernel (B1, S1, W4, SP1, SP2, P2 and W240), for oil extraction. Then, two oil extraction methods, using cold pressing (CP) and microwave preheating (MP), respectively, were investigated. In evaluation of cashew kernel grades, the fat content varied between 51.6 and 57.6 g 100 g^?1, and the acidity and peroxide were low, indicating good chemical quality for all grades. The oil extracted by MP showed a higher induction time in the Rancimat test (46.25 h). The cashew nut oil showed bioactivity, mainly associated with the level of total phenolic compounds (CP: 202.17 mg 100 g^?1; MP: 371.95 mg 100 g^?1), and showed antiproliferative activity against cancer cells (lung, breast and liver) but only at high concentrations. The MP extraction preserved many components and increased the phenolic compounds in the cashew kernel oil, without promoting negative changes in its physicochemical and oxidative qualities.     

Comparison of near‐infrared emission spectroscopy and the Rancimat method for the determination of oxidative stability

This work presents a comparison between a new method for the determination of the oxidative stability of edible oils at frying temperatures, based on near‐infrared emission spectroscopy (NIRES), and the Rancimat method at 110 °C. In the NIRES‐based method, the induction time (IT) is determined by means of the variation of the emission band at 2900 nm during heating at 160 °C. The comparison between the IT values obtained with the two methods for 12 samples of edible oils shows some correlation for samples of the same type once there is an agreement on the sequence of highest to lowest IT values between the methods, but a poor correlation considering all samples (correlation coefficient of 0.78). This lack of correlation demonstrates that the results obtained with the Rancimat method cannot be used as an indication of the oxidative stability, or the resistance to degradation, of edible oils at frying temperatures. The difference in the heating temperatures used in the two methods leads to 20–36 times higher IT values for the Rancimat method in relation to the NIRES‐based method, but with similar repeatabilities (2.0 and 2.8%, respectively).     

Shelf-life prediction of olive oils using empirical models developed at low and high temperatures

Induction period of the formation of hydroperoxides and conjugated dienes at 50 °C and oxidative stability index at 100–130 °C as the oxidative stability measures of different types of olive oils with a wide range of chemical compositions were determined. Regression models (R² ? 0.95) developed at low and high temperatures showed different contributions of compositional variables (the ratio between monounsaturated and polyunsaturated fatty acids, the content of total tocopherols and phenolics, peroxide value, acid value, and total polar compounds content) to the oxidative stability measures. To estimate the shelf-life of olive oils at low temperature, three empirical models with errors of ±1.5%, <±10%, and ±21.2% were developed.     

Oxidative stability of potato chips determined by Rancimat

During recent years the Rancimat apparatus has been used extensively to determine the stability of fats and oils. Most stability tests for fat-containing foods are performed on the extracted oil. The objective of this research was to observe the behavior of potato chips in the racimat without oil extraction. Determinations were carried out at 110°C and 20 L/hr air flow. The curves for the ground chips were completely different from those obtained with extracted oils. Curves for fresh potato chips showed two inflection points after approximately 5 and 20 hr, respectively. Sensory analyses (odor score) of samples withdrawn from the Rancimat after 0, 5, 10, 20 and 25 hr showed significant differences (P < 0.01). An odor score of 5 was considered the rejection point, and was equivalent to 10.8 hr and corresponded to 150 μs of electric conductivity. At this point, the curves started to level off between the first and second inflection points. Curves obtained with potato chips stored at 25°C for 2, 4, 6, 8, 10 and 12 wk showed the same basic pattern, although prolonged storage corresponded with lower induction time. Correlation of induction values between ground potato chips and extracted oil was high (r > 0.87). From these results, it seems that it is possible to estimate the oxidative stability of fatcontaining foods without prior extraction. Presented at 81st AOCS Annual Meeting, Baltimore, MD, 1990.     

Antioxidant properties of lipoic and dihydrolipoic acid in vegetable oils and lard

 The properties of lipoic and dihydrolipoic acid in lard and various vegetable oils were investigated as regards their use as antioxidants in food. The measurements were taken by automated Swift-test (Rancimat). Lipoic acid as well as dihydrolipoic acid proved to be antioxidants, although prooxidant effects occurred in low concentrations. The antioxidant effect increased with rising concentration. Fats containing lower levels of polyunsaturated fatty acids were better stabilized than those containing high levels. Mixtures of ascorbyl palmitate with lipoic acid or dihydrolipoic acid were more effective than the separate acids. There were additive as well as synergistic effects. The antioxidant effect of ascorbyl palmitate limited by solubility could be increased considerably by combining it with lipoic or dihydrolipoic acid. Received: 26 May 1998 / Revised version: 3 August 1998