Oxidation of Cyclo-Lino Peptides in Linseed Oils during Storage

Abstract

Linseed oil is appreciated for its high level of linolenic acid. In order to avoid oxidation, the precious storage lipids are protected in the seeds by lignans, tocopherols, and cyclo-lino peptides. Oxidation of specific cyclo-lino peptides can be attributed to the formation of a bitter off-taste in cold pressed linseed oils. A complete degradation of tocopherols and of intact cyclo-lino peptides CLO, -M, -N, -L, and -B to oxidized forms is observed with intermediate oxidation products of the peptides containing methionine oxidized to methionine sulfoxide and further to methionine sulfone during a storage period of 25 d at 60 °C in the dark and of 14 weeks at day light and room temperature. The peroxide value increases to 255 meq O2 kg−1 at the same time. However, during storage at room temperature in the dark only a very limited decrease of the initial tocopherols content of 400 mg/100 g is observed contrasted by an increase of the peroxide value to about 50 meq O2 kg−1 and a more or less complete degradation of cyclo-lino peptides. While at 6 °C in the dark all oxidation parameters keep stable. The tocopherols and cyclo-lino peptides show different and independent degradation during these storage conditions. Practical Application: This work elucidates the role of cyclo-lino peptides and tocopherols in the complex reactions taking place during oxidation of linseed oil and enables a first evaluation of the antioxidative power of cyclo-lino peptides at different storage conditions.