Natural antioxidants produced in oxidized lipid/amino acid browning reactions

1‐Substituted pyrroles ( 1 and 2 ) and 1 ‐substituted 2‐(1′‐hydroxypropyl)pyrroles ( 3–5 ) were produced in reactions between a lipid peroxidation product, 4,5( E )‐epoxy‐2( E )‐heptenal, and the amino acid lysine. The antioxidative activity of compounds 1–5 was studied. Oxidative stability was evaluated in refined soybean oil containing compounds 1–5 , butylated hydroxytoluene (BHT), n ‐propyl gallate or l ‐lysine, at concentrations of 50–200 ppm. Oils were either oxidized at 60°C and oxidation products determined by the thiobarbituric acid‐reactive substances assay, or they were oxidized at 110°C by the Rancimat method. Although both methods gave similar results, greater differences were observed at 60°C than at 110°C. Addition of compounds 1–5 , l ‐lysine, BHT, and propyl gallate significantly ( P <0.01) protected the oil against oxidation. The effectiveness order found was: l ‐lysine << compounds 3–4 < compounds 1–2 < compound 5 ≈ BHT << propyl gallate.