Photo and thermal stress of linseed oil and stabilization strategies.

The thermal and light stability of linseed oil has been studied by monitoring the concentrations of fatty acids and lignans, as main nutraceutical components. Linseed oil was subjected to stressing light and temperature conditions, in accordance with the ICH international rules, and monitored by UV-vis spectroscopy and HPLC-DAD. The change of UV spectra along the photodegradation tests, setting the irradiation power at 350 W/m, confirmed a significant overall sensitivity of linseed oil to light. At the same time, the HPLC determination of the major fatty acids showed a marked variation in their concentration up to a residual concentration of 62.3 and 67.2% for α-linolenic and linoleic acid, respectively, after 18 h. In contrast, thermal tests at 60 °C showed some stability, with a concentration of residual fatty acids in the range 82-95% after 48 h. The examined lignans showed significant stability when exposed to both light and heat. Several photoprotection approaches have been also studied to increase the photostability of linseed oil. A significant increase in the stability of fatty acids has been observed using amber glass containers or ascorbic acid or by combining the two protection factors.