An Investigation of the Non Volatile Decomposition Products in Heated Oils

This work describes the development of methods to separate and examine the non volatile decomposition products from heated oils. These methods include:
i)A Bond Elut procedure that allows a heated oil to be separated into an unchanged triglyceride extract and an extract containing the non triglyceride decomposition products. This enables the major unchanged components of the oil to be separated from the components of interest.
ii)A Gel Permeation Chromatography procedure to further separate the non triglyceride decomposition product extracts, to give an indication of the relative molecular masses of the components present and to compare these with the relative molecular masses of triglycerides.
iii)A High Performance Liquid Chromatography procedure for the separation of monomer, dimer and trimer acids of oleic acid, in order to examine samples of the non triglyceride decomposition product extracts after hydrolysis for the presence of dimer and trimer acids.
iv)A Gas Chromatography procedure for examining the GPC fractions from the non triglyceride decomposition product @xtracts after silylation, for the presence of groups which can be silylated.
Methods were initially developed using thermally oxidised oils. Standard triolein and trilinolein were then thermally oxidised to monitor the formation of decomposition products. Olive oil, rapeseed oil and peanut oil were also thermally oxidised and the decomposition products monitored.
This work shows that even for triolein, thermally oxidised at 180°C for 30 minutes, a wide range of decomposition products are present. These are of similar molecular mass to triolein and dimers of triolein. There is evidence from IR and NMR examination that there are a variety of components of similar molecular mass to triolein. Other groups including hydroxyl groups are present and there is less unsaturation than triolein. GC also indicates the presence of silylatable groups.
There is an indication that both intra and inter molecular bonds are formed on thermal oxidation to give rise to dimer and trimer triglycerides.
A method that could be used as a quality control technique for monitoring heated oils has been devised. This combines the Bond Elut extraction technique and GPC of the non triglyceride extract from this separation. The method is of use in the detection of thermally oxidised components in an oil at an early stage in the heating process.