High-temperature pre-conditioning of rapeseed: A polyphenol-enriched oil and the effect of refining

In this work, a pretreatment process for rapeseeds, which involves the use of high-temperature steam, is presented. This method, besides accomplishing the beneficial effects of the conventional industrial thermal treatment, leads to an enrichment of some important minor compounds (polyphenols and phosphatides) in the resulting oil. Rapeseeds were pretreated at different operative conditions. Then, the seeds were pressed and the press-cake was solvent extracted. The obtained oils were then refined by both chemical and physical refining techniques, and the influence of each refining step on the content of minor compounds was evaluated. The results show that the amounts of polyphenols and phospholipids present in the oil coming from pretreated seeds increase and that their concentrations depend on the conditioning time. The polyphenols present in the oil correspond mostly to 2,6-dimethoxy-4-vinylphenol (vinylsyringol). The content of polyphenols was only slightly reduced during degumming. Neutralization resulted in a complete removal of these minor compounds. For the physical refining process, the type and amount of bleaching clay used had a significant influence on the content of polyphenols. After deodorization, oil samples with a considerable amount of polyphenols were obtained. These samples show a higher oxidative stability than chemically refined oils.