To gain an understanding of the mechanism by which silicone oil (SO) suppresses the thermal deterioration of a frying oil, the following experiments were carried out.
1) Soybean and linseed oil without and with 1ppm SO were heated in an oven or plate heater for 4, 6h, at 50, 70, 90, 110 and 130°C. The degree of deterioration of these heated oils was evaluated by POV, COV and the viscosity ratio. Oils heated on the plate heater deteriorated much more than those heated in the oven. SO had a protective effect on all oils used in this experiment, particularly on those heated on the plate heater.
2) Linseed oil without and with 1ppm SO was heated under a stream of nitrogen for 16, 32 and 48h at 220°C. The degree of deterioration was evaluated by the viscosity ratio. The ratio of viscosity of heated linseed oil with SO was just the same as those without SO.
Linseed oil fatty acid methyl ester (LFM) without and with 1ppm SO was heated under a stream of nitrogen at 150°C, 180°C and 240°C. The iodine value and ratio of viscosity showed that SO had no protective effect on the methyl esters of linoleic and linolenic acid. Tung oil with and without 1ppm SO was heated under a stream of nitrogen for 10, 20, 30, 40 and 60min, at 220°C. The degree of polymerization was evaluated by the ratio of viscosity and reflactive index. SO was found to have no protective effect on tung oil. It was thus concluded that under the stream of nitrogen, SO has no protective effect on either non-conjugated or conjugated unsaturated glyceride.
