Use of a complex of formula I, or of a detergent comprising a complex of formula I, [M n+ L m-](A q+) p (X v-)r in which the metal ions M n+ are selected from Al 3+, Ti 4+, Y 3+, Zr 4+, Ce 3+, Ce 4+, Sc 3+, Yb 3+, La 3+, Ta 5+ and their mixtures, n stands for a number in the range of 1 to 5, L stands for a ligand according to formula II, in which E is selected from O, NR 1, and mixtures of them, R 1 is selected from H, optionally substituted C 1-20 -alkyl or heteroalkyl groups, optionally substituted C 2-20 -alkenyl, heteroalkenyl or alkinyl groups, optionally substituted aryl or heteroaryl groups, and optionally substituted C 1-20 -alkylaryl or heteroaryl groups, m stands for a number in the range of from 0 to 3, A stands for an alkali metal cation and q stands for 1, an earth alkali metal cation and q stands for 2, or an ammonium cation and q stands for 1, X v- stands for an anion selected from the group of F -, Cl -, Br, I -, OH -, HSO 3 -, SO 3 2-, SO 4 2-, HSO 4 -, NO 2 -, NO 3 -, PO 4 3-, HPO 4 2-, H 2 PO 4 -, BF 4 -, PF 6 -, ClO 4 -, organic anions such as acetate, citrate, formiate, glutarate, lactate, malate, malonate, oxalate, pyruvate, tartrate, methanesulfonate, methyl sulfate, tosylate, succinate and their mixtures, with v being 1, 2 or 3, respectively, and p and r, irrespective of each other, are numbers in the range of from 0 to 7, selected such that the charge of the complex according to formula I is 0 to remove cooked-, baked- and burnt-on proteinaceous soils from surfaces, preferably hard surfaces, or textile surfaces. in which the metal ions M n+ are selected from Al 3+, Ti 4+, Y 3+, Zr 4+, Ce 3+, Ce 4+, Sc 3+, Yb 3+, La 3+, Ta 5+ and their mixtures, n stands for a number in the range of 1 to 5, L stands for a ligand according to formula II, in which E is selected from O, NR 1, and mixtures of them, R 1 is selected from H, optionally substituted C 1-20 -alkyl or heteroalkyl groups, optionally substituted C 2-20 -alkenyl, heteroalkenyl or alkinyl groups, optionally substituted aryl or heteroaryl groups, and optionally substituted C 1-20 -alkylaryl or heteroaryl groups, m stands for a number in the range of from 0 to 3, A stands for an alkali metal cation and q stands for 1, an earth alkali metal cation and q stands for 2, or an ammonium cation and q stands for 1, X v- stands for an anion selected from the group of F -, Cl -, Br, I -, OH -, HSO 3 -, SO 3 2-, SO 4 2-, HSO 4 -, NO 2 -, NO 3 -, PO 4 3-, HPO 4 2-, H 2 PO 4 -, BF 4 -, PF 6 -, ClO 4 -, organic anions such as acetate, citrate, formiate, glutarate, lactate, malate, malonate, oxalate, pyruvate, tartrate, methanesulfonate, methyl sulfate, tosylate, succinate and their mixtures, with v being 1, 2 or 3, respectively, and p and r, irrespective of each other, are numbers in the range of from 0 to 7, selected such that the charge of the complex according to formula I is 0 to remove cooked-, baked- and burnt-on proteinaceous soils from surfaces, preferably hard surfaces, or textile surfaces. E is selected from O, NR 1, and mixtures of them, R 1 is selected from H, optionally substituted C 1-20 -alkyl or heteroalkyl groups, optionally substituted C 2-20 -alkenyl, heteroalkenyl or alkinyl groups, optionally substituted aryl or heteroaryl groups, and optionally substituted C 1-20 -alkylaryl or heteroaryl groups, m stands for a number in the range of from 0 to 3, A stands for an alkali metal cation and q stands for 1, an earth alkali metal cation and q stands for 2, or an ammonium cation and q stands for 1, X v- stands for an anion selected from the group of F -, Cl -, Br, I -, OH -, HSO 3 -, SO 3 2-, SO 4 2-, HSO 4 -, NO 2 -, NO 3 -, PO 4 3-, HPO 4 2-, H 2 PO 4 -, BF 4 -, PF 6 -, ClO 4 -, organic anions such as acetate, citrate, formiate, glutarate, lactate, malate, malonate, oxalate, pyruvate, tartrate, methanesulfonate, methyl sulfate, tosylate, succinate and their mixtures, with v being 1, 2 or 3, respectively, and p and r, irrespective of each other, are numbers in the range of from 0 to 7, selected such that the charge of the complex according to formula I is 0 to remove cooked-, baked- and burnt-on proteinaceous soils from surfaces, preferably hard surfaces, or textile surfaces.