INHIBITED OXIDATION OF LIPIDS .1. COMPLEX ESTIMATION AND COMPARISON OF THE ANTIOXIDATIVE PROPERTIES OF SOME NATURAL AND SYNTHETIC ANTIOXIDANTS

The activity A of antioxidants, representing a ratio between the stabilization factor F and the decrease in oxidation rate after the introduction of an inhibitor DOR (A = F/DOR) is Proposed for a complex estimation of the effect of antioxidants. The specific changes in F, DOR and A are discussed in association with the participation of the inhibitor molecule and the radical formed from it in the different reactions of initiation and propagation of the chains. Several types of antioxidants (alpha-tocopherol, ferulic acid, BHT and BHA) in concentrations ranging from 0.02 - 0.20 wt% are investigated during the oxidation of lard at 100-degrees-C. It is established that at concentrations of 0.02-0.05 wt% the antioxidative activity increases in the sequence ferulic acid < BHT < BHA < alpha-tocopherol. At high concentrations (above 0.10 wt%) the activity increase follows the sequence alpha-tocopherol < BHT < BHA < ferulic acid. Enhancement of the antioxidant concentration above 0.02 wt% is expedient only in the case of ferulic acid. The molecules of alpha-tocopherol, BHA and BHT participate not only in chain termination but also in first order rate side reactions with respect to the inhibitor, which explains the decrease in their efficiency with rising concentration. The molecule of ferulic acid does not participate in side reactions. The aroxyl radical formed from BHT does not participate in chain propagation, whereas the radicals of BHA and ferulic acid take part in such reactions. The aroxyl radical of alpha-tocopherol joins in more than one side reactions.