slightly decomposes under repeated thermal treatments, followed by volatilization, but the antioxidative effect is maintained very well in heated oil. This is the big reason why PDMS is added to heavy-duty oil as an antioxidant in addition to its safety. Canola oil containing only 0.1 ppm PDMS looks slightly turbid, is lighter in touch, and absorbs into skin slower than canola oil. The smell of canola oil is reduced by the addition of PDMS. However, it is not easy even by analytical instruments

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... to confirm if PDMS in oil in the ppb to ppm range is dispersed or dissolved due to its low solubility. Available PDMS is a polymer of dimethylsiloxane with a certain degree of polymerization. This makes our understanding more complicated. Freeman et al. 9 reported that PDMS formed a monolayer on an oil surface and that oxygen in the air was inhibited from penetration and diffusion in oil, resulting in an antioxidative effect. However, when the oil surface is disturbed Abstract: It has been reported that polydimethylsiloxane (PDMS) inhibits oxygen dissolution into oil by forming a monolayer on the surface of the oil, thereby reducing thermal oxidation. In the present study, the distribution of PDMS was determined by the inductively coupled plasma atomic emission spectroscopy in standing PDMS-containing canola oil. PDMS did not disperse in the oil uniformly, but there was a tendency that the PDMS concentration decreased as the depth of oil increased, and the concentration of the bottom part was the lowest. When canola oil was covered with PDMS by dropping it gently on the surface of the oil and kept at 60℃, the oxygen content and oxidation of the oil were lower than those of the control canola oil. PDMS-containing canola oil and canola oil were heated with stirring from room temperature to 180℃, and then allowed to stand while cooling. Oxygen contents of both oils increased up to 120℃ then dropped abruptly. While cooling, oxygen contents sharply increased at 100℃ and approached the saturation content, although the increase for PDMS-containing canola oil was a little slow. Likewise, the thermal treatment of PDMS-containing canola oil and canola oil at 180℃ for 1 h under stirring was repeated 5 times with standing intervals for 2-3 days at room temperature. Oxidation of the former was less than that of the latter in spite of its high oxygen content. In conclusion, the oxygen content of oil with/without PDMS addition increased, but oxidation of PDMS-containing canola oil was inhibited both during heating and standing with intermittent heating. It was suggested that PDMS exerted its antioxidative effect regardless of whether it covered the oil or was dispersed in it.