With a market share of 15 %, rapeseed oil is one of the most important vegetable oils. It is a good source of polyunsaturated fatty acids (PUFAs), oil-soluble vitamins and antioxidants in the human diet. Małgorzata Tanska and colleagues, University of Warmia and Mazury, Olsztyn, Poland, investigated the chemical composition of 21 different commercial types of rapeseed oil (cold pressed, extracted, mixed, unrefined and refined) at two different time-points: Directly after opening the bottles and then again at the end of their induction period. This moment marks the transition from a slow induction period to the subsequent fast chain-reaction in oxidation.

Several freshly opened oils show only slight differences in fatty acid composition, but a higher variation in carotenoids and phenolic compounds. At the end of the induction period, the fatty acid composition still is relatively stable, but fat-soluble compounds vary significantly among different oils. The length of the individual induction period correlates positively with the amount of phenolic compounds, whereas carotenoids seem to have a pro-oxidative effect.

The manufacturing process thus not only affects the initial quality of the oil, but also its oxidative stability.

• Variation in the composition and oxidative stability of commercial rapeseed oils during their shelf life,
  Beata Roszkowska, Małgorzata Tańska, Sylwester Czaplicki, Iwona Konopka,
  Eur. J. Lipid Sci. Technol. 2014.
  DOI: 10.1002/ejlt.201400271