Vegetable Oil Stability at Elevated Temperatures in the Presence of Ferric Stearate and Ferrous Octanoate

The thermoxidative stability of partially hydrogenated soybean oil (PHSBO) was examined after addition of ferric stearate and ferrous octanoate, and then heating the samples at 120, 160, 180, and 200 °C. In a second experiment, the effect of iron concentration (ferric stearate) on PHSBO stability was examined at 180 °C, and at concentrations of approximately 0.5 and 1.2 mg of added iron/kg PHSBO. Oil samples were heated continuously for 72 h and sampled every 12 h. The acid value, p-anisidine value, color, dielectric constant and the triacylglycerol polymer content of oil samples were compared to oil samples containing no added iron. Generally, the value of each oxidative index increased with (1) an increase in temperature, (2) an increase in heating time, and/or (3) an increase in iron. The results demonstrate that low concentrations of iron will substantially increase the rate of oxidation for vegetable oil samples heated to temperatures of 120 °C to 200 °C. Keywords: oil stability; thermo-oxidative stability; iron; soybean oil; deep-fat frying