Determination of oxidative stability in mixtures of edible oil with nonlipidic substances

The storage of lipid foods is mostly affected by the oxidation of lipid fraction. Dry foods are particularly sensitive because lipids are not protected by hydrated proteins against oxidation. A method suitable for testing dry foods was studied in model mixtures of rapeseed oil with albumin or cellulose. Oxipres apparatus was used, where the course of oxidation is monitored by changes of oxygen pressure. The end of induction period was more evident than in bulk oils as the contact of lipids with oxygen is better. The induction period was longer in mixtures of edible oil with albumin than in mixtures with cellulose. The induction period moderately decreased with increasing oxygen pressure, while the effect of sample weight was nearly negligible. The induction period length was a semilogarithmic function of reaction temperature. Variation coefficients and differences between the duplicates showed good reproducibility; they were lower in mixtures with albumin than in mixtures with cellulose, but both were of the same order as the respective values in bulk oils. At 120°C and 0.5 MPa oxygen, the induction periods could be usually measured within a working day.