Autoxidation of Methyl Linoleate in Freeze‐Dried Model Systems. II. Effect of Water on Cobalt‐Catalyzed Oxidation

Abstract

SUMMARY The oxidation of methyl linoleate catalyzed by various salts of cobalt was studied in a model system based on microcrystalline cellulose. The freeze‐dried model system was adjusted to various water activities, and the effect of water on the oxidation kinetics was determined using manometric measurements and measurements of diene conjugation. It was found that water had an inhibitory effect on the metal‐catalyzed oxidation of the fatty ester, as well as on oxidation in the absence of added metals. The kinetics of the reactions were evaluated in terms of the previously established hydroperoxide decomposition mechanisms. The effect of water on the metal‐catalyzed oxidation was found to exist in the monomolecular decomposition period as well as in the more rapid phase of the reaction, during which the hydroperoxide decomposition is known to follow bimolecular decomposition kinetics. The inhibition of the reaction by water is interpreted as due to deactivation of added, as well as of originally present, metal catalysts by hydration of the coordination shells; and also possibly as due to hydrogen bonding between hydroperoxides and water, and therefore to interference with the normal bimolecular decomposition reaction.

Stabilization of Emulsion and Butter like Products Containing Essential Fatty Acids Using Kalonji Seeds Extract and Curcuminoids

“…The use of synthetic antioxidants can be avoided as there are various easily available natural products that contain antioxidants. The natural antioxidants like curcuminoids and KEE are non-toxic and moreover they retain their antioxidant activity in functional foods like emulsions and BLPs as water affects the stability of EFAs negatively 22,23 .…”

Ação antioxidante de especiarias face diferentes atividades de água

“…Estes resultados encontram apoio nos de KAREL et al [14], LABUZA, TSUYUKI & KAUL [15] e MALONEY, KAREL & LABUZA [21] que em sistemas semelhantes, contendo catalisadores metálicos, observaram um efeito protetor crescente da água desde Aw 0,00 até Aw 0,30 -0,50, pontos de oxidação mínima.…”

Solvent Techniques for the Direct Colorimetric Determination of Copper and Iron in Oils

“…In the course of a research project on the catalyzed oxidation of methyl linoleate (Labuza et al, 1966) it was found necessary to develop a simple technique for trace metal analysis (iron and copper) in the lipid. The requirements for the analyses included a minimum of losses 3s well as a minimum sample size (up to l-2 g) .…”