Characterization of complex phenolic compounds in rapeseed and sunflower biomass generated during biorefinery

International audience

English. In addition to lipids, proteins and polysaccharides, rapeseed and sunflower seeds are known to be rich in phenolic compounds. They are located both in the seeds and in their fibrous hulls. After oil production, it’s very interesting to valorize these phenolic compounds due to their putative benefits in cancer and heart disease. The rapeseed polyphenols include sinapine, derivatives of sinapic acid, flavonols and condensed tannins while sunflower seeds contain mainly chlorogenic acids. Previous studies reported that the concentration of some complex polyphenols such as condensed tannins in rapeseed hulls tends to decrease with advanced plant maturity. They may be oxidized or form strong interactions with other polymers in the plant (proteins, polysaccharides). Therefore, new methods of extraction and characterization should be developed for a better valorization of such biomass feedstock generated during biorefinery.Our work aims at evaluating the applicability of direct phloroglucinolysis and butanol-HCl method for determining complex phenolic compounds in rapeseed and sunflower biomass (oil cake and hull). After delipidation, phloroglucinolysis or butanol-HCl reactions were applied directly to the samples. The amount and profile of polyphenols were analyzed both by spectrophotometry and by LC/MS. Results show that the rapeseed hulls contain 0,85 g/kg (after phloroglucinolysis) and 0,69 g/kg (after butanol-HCl) of condensed tannins. Combined effect of pretreatment by SDS reagent (60 min, 50 °C) and butanol-HCl analysis results in a higher value of condensed tannins content in the rapeseed hulls (1,55 g/kg). This may be due to the fact that the permeability of plant material is increased after organic solvent pretreatment which makes the condensed tannins more accessible to the acidolysis reaction. However, the content of condensed tannins could still be underestimated since both methods are insufficient to analyze oxidized phenolic compounds. Compared to rapeseed hulls, less condensed tannins were detected in rapeseed oil cakes and in sunflower samples. Future studies will be focused on the optimization of analysis methods for a better characterization of oxidized phenolic compounds.