The present invention relates to a composition which comprises at least one α,ω-amino-alkanoic acid or ester and at least one alkanoic ester or acid, characterised in that: the α,ω-amino-alkanoic acid or ester has formula H2N—(CH2)n-COOR, wherein n=9 to 13 and R is an alkyl group or a hydrogen; the alkanoic ester or acid has formula R1—COOR2, wherein R1 is a straight or branched alkyl group with formula CmH2m+1 or CmH2m−3, wherein m=6 to 20 and R2 is an alkyl group or a hydrogen; the molar ratio between the alkanoic acid(s) or ester(s) and the α,ω-amino-alkanoic acid(s) or ester(s) is in the range from 0.001 to 0.4%. The present invention also relates to novel methods for obtaining such a composition.