Food pink discoloration

Hong, C.M., Wendorff, W.L., and Bradley, R.L., Jr., Factors affecting light-induced pink discoloration of aimatto-colored cheese, J. Food ScL, 60, 94, 1995. 

Hong, C.M., Wendorf, W.L., and Bradley, R.L. 1995. Effects of packaging and lighting on pink discoloration and lipid oxidation of annatto-colored cheeses. J. Dairy Sci. 78, 1896-1902. Homero-Mendez, D. and Minguez-Mosquera, M.I. 1998. Isolation and identification of the carotenoid capsolutein for Capsicum armuum as cucurbitaxanthin A. J. Agric. Food Chem. 46,4087 1090. Humphrey, A.M. 1980. Chlorophyll. Food Chem. 5, 57-67. 

In stored foods containing natural bixin (9 -ds isomer), in the presence of light, aU-trans-bixin may result and, by its hydrolysis, all-trfl s-norbixin. In cheeses containing bixin, these substances bind to phosphoproteins (e.g. to some caseins), causing pink discoloration of products. In addition to tra s-isomers, some degradation products of bixin may also arise, such as methyl ester of d -trans-4,8-dimethyltetradeca-2,4,6,8,10,12-hexaenoic acid and aromatic hydrocarbons (e.g. m-xylene). 

In some cases, however, the formation of salts and complexes is an unwanted phenomenon, as protein salts and complexes with polyphenols form hazes and sediments in preserved fruit, fruit juices and beer. Protein hazes can also form in white wines after bottling, where the main factor is inorganic sulfate ions. Protein complexes with transition metals are often coloured, and their formation in processed foods is generally undesirable. An example is the protein conalbumin occurring in egg white, which readily forms coloured complexes with metal ions (pink with Fe +, yellow with Cu + and Mn +) in media of pH > 6 through tyrosine and histidine residues of the polypeptide chain. Complexes with iron ions often cause discoloration of egg products, but in media with pH < 4, these complexes dissociate to the original colourless compounds. 

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