Relating patatin and lipoxygenase variant profiles to enzymatic activities in potato protein isolates

In potato protein isolates, lipases and lipoxygenases catalyse unpleasant off-taste reactions, which hamper the application of these ingredients in food products. Protein isolates from different potato cultivars vary notably in enzymatic activities despite similar processing histories and protein content. Lipases and lipoxygenases exist as multiple genetic variants, which may influence these activities. To explore this, protein extracts from eight potato cultivars were analysed for enzymatic activities and the variant profiles were investigated using a UHPLC-MS approach. Additionally, glycosylation and phosphorylation levels of lipase and lipoxygenase were examined. Lipase and lipoxygenase activities varied tenfold and fourfold across cultivars, respectively, but no correlation was found between variant profile and enzymatic activity. Furthermore, lipase variants were all glycosylated but not phosphorylated, while lipoxygenase variants lacked post-translational modifications. The results indicate that the differences in lipase and lipoxygenase activities between cultivars cannot be explained by the variant profile and glycosylation or phosphorylation levels.