Functionalized alternan, comprising carboxy groups as functional groups, wherein the alternan can be described by the following formula (I) Alternan (I) wherein R1 is a hydrocarbon group with 1 to about 100 carbon atoms, optionally featuring one or more heteroatoms, wherein the oxygen between “Alternan” and R1 in Formula (I) is an oxygen of an ether group, as well as the procedures for producing such a functionalized alternan in a aqueous medium or using an alcohol or an alcohol-water mixture as a reaction medium, and the use of this functionalized alternan.