Characterisation and quantification of condensed tannins in rapeseed hulls and meals by depolymerization methods

International audienceCondensed tannins (i.e. polymerized procyanidins) were quantified in crude samples of rapeseed meal and hullsusing two acidolysis methods. When it was applied directly on crude material, the colorimetric butanol-HCl assayallowed an estimation of two grams of tannins per kilogram of dried hulls. Interestingly, the estimation was morethan double after solvent extraction using sodium dodecyl sulphate (SDS) when the colorimetric method wasapplied on both the extract and the insoluble residue. By altering the plant tissues organization, SDS treatmentmay allow a better accessibility of the depolymerizing reagents. However, this colorimetric assay was judgedapproximate because of browning side-reaction likely involving other components. Phloroglucinolysis combinedwith HPLC-UV-MS analysis was more rigorous and informative confirming that rapeseed hulls condensed tanninswere essentially constituted of epicatechin units with an average degree of polymerization of close to 11. Ac-cording to this method, the concentration of condensed tannins in hulls was estimated to 5.19 g/kg in theoptimized conditions established through a factorial experimental design allowing optimization of hydrochloricacid concentration, reaction duration and temperature