Lipoxygenase-mediated peroxidation of model plant extractives

Abstract

Three unsaturated fatty acids, namely 9-cis,12-cis-linoleic acid, 1,2,3-tri-cis, cis-9,12-octadecadienoyl (glycerol trilinolein) and 1,2,3-tri-cis-9-octadecenoyl (triolein) were selected as models of components of plant extractives to monitor the hydroperoxygenation induced by soybean lipoxygenase (LOX), which was applied as an oxidative catalyst at room temperature. The fatty acids were monitored in colloidal dispersions in relation to their molecular changes using 1H/13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and UV spectroscopies. The detection of the hydroperoxy group was limited due to its unstable nature. However, the reduction of protons associated with the diene groups and the substitution of hydroperoxy groups at the allylic positon in conjugated lipids were detected by the induced chemical shift of HOO-bearing 13C and 1H resonances and the oxygen absorption owing to changes in the molecule. Moreover, compared to the two other substrates, no oxygen substitution was observed in triolein, in accordance with its lower level of saturation and the absence of bis-allylic carbon. Our results are of relevance to plant fiber processing, since fatty acids are major constituents of hydrophobic deposits that cause a range of manufacturing challenges.