The 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 α- and γ-tocopherols, 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 α-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.

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

Publisher Summary The composition of olive oil is primarily triacylglycerols (~99%) and secondarily free fatty acids, mono- and diacylglycerols, and an array of lipids such as hydrocarbons, sterols, aliphatic alcohols, tocopherols, and pigments. A plethora of phenolic and volatile compounds are also present. Some of these compounds contribute to the unique character of the oil. Fatty acids present in olive oil are palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0), oleic (C18:1), linoleic (C18:2), and linolenic (C18:3). Myristic (C14:0), heptadecanoic, and eicosanoic acids are found in trace amounts. This chapter discusses some classes of minor constituents that are present only in the crude oil. Filtration reduces the initial levels to a great extent whereas refining results in their removal.

Olive Oil Composition

Chemical and structural characterisation of almond oil bodies and bovine milk fat globules

Extra virgin olive oil is produced in the form of a “suspension–dispersion” which canpersist for several months before full deposition of a residue. Many consumers andchefs prefer unfiltered raw olive oil because it looks thicker and richer in flavors. Thenature of the material in the suspension–dispersion is poorly described. The presenceofproteinshasbeenconnectedwiththeappearance ofthe“veiled”oilandalsowithitsoxidative stability, although there are discrepancies in the literature with regard to theirlevels. The level of phosphorus, a measure of phospholipids, is also poorly studied.This work aims at quantifying proteins and phospholipids in cloudy olive oil. For theanalysisofproteins,apractical methodisusedthatcanbeappliedforroutineanalysis.The proteins are precipitated with acetone and determined colorimetrically using theBradford method suitably modified to measure protein dye-binding at low concentra-tions. Twenty three virgin and one refined olive oil samples from different places inGreece were all found to have protein levels below 2.5mg/kg. In most of the samples,values were lower after filtration of the cloudy oils. In the refined oil samples, proteinwas hardly determined (value 0.1mg/kg). Phosphorus levels ranged from 0.8 to4.8mg/kg. These correspond to approximately 21–124mg/kg of phospholipids. Theresults are discussed in relation to the oxidative and physicochemical stability of theveiled oils.

The contents of proteins and phospholipids in cloudy (veiled) virgin olive oils

Quality of olives: A focus on agricultural preharvest factors

HPLC employing a thermostatted Lichrospher 100 diol column was used to separate mixtures of glycerophospholipids of rapeseed, olive, almond, and sunflower oils. Elution was performed with a binary ...

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Khaled Sebai

Papers

Identification of glycerophospholipids in rapeseed, olive, almond, and sunflower oils by LC-MS and LC-MS-MS