Browsing by Subject "tokoli"

Oat has a high content of lipids compared to many other grains. Oat contains lipid hydrolysing enzyme, lipase, and unsaturated fatty acids, which are prone to oxidation. Hydrolytic reactions and oxidation of lipids may cause major quality changes in oats. Oat contains also phenolic antioxidants - tocols, avenanthramides and phenolic acids - that may inhibit lipid oxidation. The aim of this research was to examine how tocols, avenanthramides and phenolic acids act as antioxidants in oat during lipid oxidation. The purpose was to study concentration changes of these compounds in six oat samples in storage. The storage experiment was performed for 12 weeks at 40 °C. Tocols, avenanthramides, phenolic acids and neutral lipids were analysed by liquid chromatography methods after 0, 2, 4, 8 and 12 weeks of storage. Volatile compounds were measured by a solid phase microextraction gas chromatography method. During the storage, volatile compounds, such as hexanal and 2-pentylfuran, were formed especially in groats. Free fatty acids were hydrolysed from triacylglycerols only in groats, because lipase was active in these samples. The α-tocol concentrations of oat samples decreased significantly, 45-77%, in storage. The β-tocotrienol concentrations decreased 34-53%. At the beginning of the storage avenanthramide concentrations showed 20-45% reduction. After that, the concentrations were either stable or increased 10-30%. The phenolic acid concentrations either decreased, increased or were stable during storage. The most significant change was found in unheated groats where the concentration of free caffeic acid increased even 2.6-fold during eight weeks of storage. The loss of α-tocols imply that these compounds are effective antioxidants in oat. This study did not indicate antioxidant activity of avenanthramides and phenolic acids in oat because the changes of these compounds varied in storage. However, the variation of avenanthramide and phenolic acid concentrations may have been caused by their antioxidant activity and release of bound compounds. Thus, further research is needed in order to study the effect of avenanthramides and phenolic acids in oat during lipid oxidation.