2019 Volume 19 Issue 3 Pages 93-101
Polydimethylsiloxane (PDMS) is utilized in commercial oil for frying food. It has been reported that PDMS shows extraordinarily strong antioxidative effects under thermal treatment, despite being designated as antifoamer. There are many interpretations of the theories regarding of the antioxidative effects of PDMS, such as “formation of a monolayer of PDMS at the air-oil interface” and “a decrease in the convection current of frying oil”. However, the mechanisms are still not completely understood. This report elucidates the status of PDMS and oxygen in oil and describes an examination of the antioxidative mechanism of PDMS that was performed by measuring the chemical characteristics and tocopherol content of heated oil. The addition of more than about 0.06 μg/cm2 PDMS at the air-oil interface results in PDMS forming both a layer at the oil-air interface and droplets suspended in the oil. PDMS-containing canola oil was allowed to stand at room temperature with the upper void volume replaced with nitrogen gas. The PDMS concentration and oxygen content tended to decrease as the depth of the oil increased. The oxygen content of the oil with added PDMS was higher than that without PDMS addition, but oxidation of PDMS-containing canola oil was inhibited both during heating and standing with intermittent heating. In addition, oxygen-saturated canola oil with added PDMS was placed in a vial that was hermetically sealed such that there was no air at the top. When the oil was subsequently incubated at 60°C, oxidation was markedly inhibited. These results demonstrate that the PDMS droplets exhibit an antioxidative effect separate from that of the PDMS monolayer. No antioxidative effect was observed when using either silicone oil, such as polymethylphenylsiloxane dissolved in canola oil, or PDMS in PDMS-soluble fatty acid isopropyl ester, suggesting that PDMS must be insoluble and droplets in oil for PDMS to exhibit an antioxidative effect during deep frying. The zeta potential of PDMS was –74±10.6 mV, indicating that countless PDMS droplets are stably scattered in oil. This attractive force is believed to disturb the motion of oxygen clusters and prevent their attack against unsaturated fatty acid moieties, thus suppressing oxidation by PDMS.
