Quantitative analysis of the main phenolics in rapeseed meal and oils processed differently using enzymatic hydrolysis and HPLC

Rapeseed meal is the dry residue of the rapeseed de-oiling process. It contains more phenolic compounds than any other oilseed meal. In analysis, rapeseed phenolic esters, mainly sinapine, are usually hydrolyzed to free phenolic acids, because sinapine is not available as a commercial standard. In this study, the efficiencies of different enzymes and enzyme preparations in hydrolyzing sinapine to sinapic acid were explored. The main phenolics in rapeseed meal were sinapine and sinapic acid. In rapeseed oil, the main phenolics were vinylsyringol, sinapine and sinapic acid. In hydrolyzing rapeseed meal, ferulic acid esterase and Ultraflo L were as effective in hydrolyzing sinapine as sodium hydroxide. Over 90% of sinapic acid derivatives were hydrolyzed to yield sinapic acid. Compared to base hydrolysis, enzyme treatment was not only as efficient but also less destructive to the liberated phenolics. Thus, enzymatic hydrolysis is a recommended procedure for optimal analysis of rapeseed phenolics. In rapeseed oils, hydrolysis was best applied in crude post-expelled rapeseed oils with high phenolic content.