Phenol antioxidant efficiency in various lipid substrates containing hydroxy compounds

Abstract

The oxidation stability of triacylglycerols of sunflower oil (TGSO) at 80 ?C in the presence of 0.1 mM 2, 6-di-tert-butyl-4-methylphenol (BHT) was found to decrease in the presence of 40 mM lipid hydroxy compounds (R'OH), 1-tetradecanol (1-TD), 1-octadecanol (1-OD), and 1-monopalmitoylglycerol (1-MP). Taking into account the significant effect of these compounds on the chain initiation via an acceleration of the hydroperoxide decomposition, the relative protection activity of BHT was found to increase in the presence of R'OH in the sequence: (TGSO) < (TGSO+1-TD) < (TGSO+1-OD) < (TGSO+1-MP). This result was explained with the so-called “micellar effect”: the relatively higher concentration of polar species such as hydroperoxide, peroxyl radicals and BHT within and nearby the micro aggregates formed in the presence of R'OH, leads to an increase of the rate of chain termination compared to that in the bulk lipid. When free radicals are generated in the bulk oil via the decomposition of a special nonpolar initiator, azo-bis-isobutyronitrile, 1-OD and 1-MP do not affect the BHT antioxidant efficiency. The effect of the lipid medium (linoleate or oleate type) on the antioxi-dant activity of α-tocopherol (TOH), 1.3 mM, in the presence of 1-OD has been assessed on an example of oxidation of sunflower oil (SO) and lard (L) at 100 ?C. Inspite of their different oxidizability 1-OD caused the same relative decrease in the TOH efficiency during SO and L oxidation.