Dehydration products of sitosterol, formed in vegetable oils during high temperature processing steps of the refining procedure such as bleaching and deodorization. The main product is 3,5-stigmastadiene. Stigmastadienes are not usually formed in high levels in virgin olive oils, where production involves nonthermal processes such as centrifugation and pressing. Stigmastadienes can be used as indicators of the presence of refined vegetable oils in virgin olive oils or to differentiate thermally treated oils from those that have been cold pressed.