title: On the origin and variation of colors in lobster carapace.
abstract: The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, α-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-β-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of β-crustacyanin (PDB code: ) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation.
authors: School of Chemistry, University of Manchester, Manchester, M13 9PL, UK. john.helliwell@manchester.ac.uk.
authors: Shamima
authors: S
authors: Begum
authors: Michele
authors: M
authors: Cianci
authors: Bo
authors: B
authors: Durbeej
authors: Olle
authors: O
authors: Falklöf
authors: Alfons
authors: A
authors: Hädener
authors: John R
authors: JR
authors: Helliwell
authors: Madeleine
authors: M
authors: Helliwell
authors: Andrew C
authors: AC
authors: Regan
authors: C
authors: C
authors: Ian F Watt
mesh_terms: D060105:Animal Shells / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D003116:Color; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008968:Molecular Conformation; D008121:Nephropidae; D011789:Quantum Theory; D013816:Thermodynamics; D024341:Xanthophylls / Q000737:chemistry / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D024341:Xanthophylls; C018494:crustacyanins; C005948:astaxanthine