Kinetic studies were performed to obtain the dependence of rates of lipid oxidation on oxygen pressure, in a system containing free as well as adsorbed oxygen. The model system consisted of methyl linoleate dispersed on either microcrystalline cellulose or on nonfat milk powder. Oxidations were carried out at 37°C, and with headspace concentrations of oxygen ranging from 0.52% to 10.7%. These concentrations were maintained aproximately constant by periodically resupplying oxygen to replace the amount reacted with the lipid.

Bimolecular oxidation kinetics were found in both systems with the rate of oxidation more rapid (by a factor of 5 to 6) in the cellulose system. The dependence of oxidation on oxygen pressure was of a form previously found for oxidizing lipids by other investigators, and is consistent with theoretical considerations. The slower oxidation in the milk system appeared to the due two factors: encapsulation of part of the lipid in the milk solids, and the lower internal surface area of the milk solids compared to the cellulose support.