The invention relates to a method for production of a preparation from a vegetable material, said preparation being enriched in a polysaccharide with a backbone comprising rhamnogalacturonan-I cores, said methodcomprising the steps: mixing the vegetable material with a polar alcoholic solvent; and separating a solid residue obtained in step a) from the solvent; and mixing the solid residue obtained in step b) with a buffered aqueous solution having a pH between 7 and 8. Also provided is a preparation containing rhamnogalacturonan-I pectins that can be obtained by this method and the use of such a preparation to modulate immune response.