Abstract: The effects of various exogenous substances on the changes of free radicals and 1H nuclear magnetic resonance (NMR) spectra during the oxidation of linseed oil at room temperature were investigated by electron paramagnetic resonance (EPR) and NMR spectroscopy. The results showed that the types of free radicals generated during the oxidation process under natural light or dark conditions in the presence of added tert-butyl hydroquinone (TBHQ), vitamin E (VE) or chlorophyll were 5,5-dimethyl-1-pyrroline N-oxide unknown radicals (DMPO-X), alkyl radicals (R·), alkoxy radicals (RO·) and alkoxy peroxy radicals (ROO·), while added 2,2’-azobisisoheptonitrile (ADVN) could initiate inorganic carbon-centered free radicals. Natural light was beneficial to the generation of DMPO-X; RO· was prone to form in darkness. The contents of RO· and ROO· were decreased effectively by TBHQ. VE delayed the appearance time of the highest signal intensity of DMPO-X and inhibited the formation of R·. Chlorophyll inhibited the production of DMPO-X and RO· in the early and late stages of oxidation, respectively. ADVN promoted the formation of DMPO-X in the oxidation process, and accelerated the generation of ROO· and RO· in the middle and late stage of oxidation, respectively. In conclusion, during the room temperature oxidation of linseed oil, the production and decomposition of RO· were directly related to the oxidation degree. Different exogenous substances mainly affected the content of free radicals, but had little effect on the types of free radicals.

Key words: linseed oil; room temperature oxidation; free radicals; exogenous substances; electron paramagnetic resonance