Effect of temperature and addition of α‐tocopherol on the oxidation of trilinolein model systems

The aim of this work was to study the evolution of oxidation and the efficiency of phenolic antioxidants in sunflower oil-in-water emulsions containing sodium caseinate and lactose (Cas-Lac) or stabilized by . Two groups of phenolic antioxidants which are structurally similar were tested, i.e. (1) a-tocopherol and its water-soluble analogue, Trolox; and (2) gallic acid and its ester derivatives propyl gallate and dodecyl gallate. Emulsion samples were oxidized at 40 7C and the progress of oxidation was followed through quantitation of oxidized triacylglycerol monomers, dimers and oligomers. Results showed that Cas-Lac emulsions were more stable to oxidation than T-20 emulsions. In both types of emulsions, the most protective antioxidants were the compounds of lower polarity, namely, a-tocopherol and dodecyl gallate. It was also found that substantial amounts of a-tocopherol coexisted with significant polymerization, which was indicative of the heterogeneity of oxidation, i.e. differences of oxidation rate in oil droplets.

Section: Resultssupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Antioxidant activity of phenolic compounds in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose

Velasco

Dobarganes

Márquez‐Ruiz

2004

“…This approach provided concomitant quantitation of primary and secondary oxidation compounds [17], and it has also shown to be useful to evaluate oil-containing foods oxidized at low temperature [18,19]. The results confirmed those previously reported in trilinolein, showing that the end of the IP was marked by a sharp increase in the total content of oxidation compounds, by the initiation of polymerization and by the total loss of atocopherol [20].…”

Section: Introductionsupporting

confidence: 78%

Formation of oxidation compounds in sunflower and olive oils under oxidative stability index conditions

Márquez‐Ruiz

Martín-Polvillo

Velasco

et al. 2008

Self Cite

The objective of this work was to study the evolution of oxidation under oxidative stability index (OSI) conditions using the Rancimat apparatus. Sunflower oils with different degrees of unsaturation (conventional high-linoleic sunflower oil, genetically modified high-oleic sunflower oil, and a 1 : 1 mixture of both of them) and virgin olive oil were used. The sunflower oils were tested at 100 7C, while the olive oil was assayed at 100, 110 and 120 7C. Samples were analyzed at different time points and conductivity values, until the induction period (IP) was overpassed. A combination of adsorption and size-exclusion chromatography was used for the quantification of oxidized triacylglycerol (TG) monomers, dimers and polymers. Additionally, peroxide values (PV) and ultraviolet absorption at 270 nm (K 270 ), as well as losses of tocopherols, were measured. The results showed that oxidized TG monomers were the only group of oxidation compounds that increased during the early oxidation stage. The end of the IP was marked by the initiation of polymerization after the exhaustion of tocopherols. In comparison with reported results obtained at room temperature, the main difference found was that the amounts of oxidation compounds at the end of the IP were much lower at OSI test temperatures. With the exception of the K 270 values, the results also showed that the IP endpoints provided by the OSI test were slightly higher than those obtained by quantification of oxidized TG monomers or by PV determination.

“…For example, E a was found to be ca. 42, 46, and 51 for trilinolein containing 0, 250, and 500 ppm of a-tocopherol, respectively, and E a /T was directly proportional to the induction period [44]. The inhibition of vegetable oil oxidation is usually associated with a critical minimal concentration of antioxidants [45], e.g.…”

Section: Tocopherol Contents and Oxidative Stabilitymentioning

confidence: 99%

Effect of fatty acids and tocopherols on the oxidative stability of vegetable oils

Kamal‐Eldin

2006

229

165

Effect of fatty acids and tocopherols on the oxidative stability of vegetable oilsThe oxidative stability of vegetable oils is determined by their fatty acid composition and antioxidants, mainly tocopherols but also other non-saponifiable constituents. The effect of fatty acids on stability depends mainly on their degree of unsaturation and, to a lesser degree, on the position of the unsaturated functions within the triacylglycerol molecule. Vegetable oils contain tocopherols and tocotrienols, especially a-and gtocopherols, as their main antioxidants. The antioxidant behavior of tocopherols represents a complex phenomenon as they are efficient antioxidants at low concentrations but they gradually lose efficacy as their concentrations in the vegetable oils increase. The "loss of efficacy" of tocopherols, sometimes referred to as a "pro-oxidant effect", is witnessed by an increase in the rate of oxidation during the induction period, despite elongation of this phase. The phenomenon is much obvious for a-tocopherol, but is also evident for other tocopherols. In agreement with nature's wisdom, the tocopherol levels in vegetable oils seem to be close to the optimal levels needed for the stabilization of these oils. The presence of other antioxidants in the oils, e.g. carotenoids, phenolic compounds, and Maillard reaction products, may synergize with tocopherols and minimize this loss of efficacy.