Indigo- and indirubin-producing strains of Proteus and Psychrobacter are associated with purple rind defect in a surface-ripened cheese.

Indigo- and indirubin-producing strains of Proteus and Psychrobacter are associated with purple rind defect in a surface-ripened cheese. Food Microbiol. 2018 Dec;76:543-552 Authors: Kamelamela N, Zalesne M, Morimoto J, Robbat A, Wolfe BE Abstract The rinds of surface-ripened cheeses have expected aesthetic properties, including distinct colors, that contribute to overall quality and consumer acceptance. Atypical rind pigments are frequently reported in small-scale cheese production, but the causes of these color defects are largely unknown. We provide a potential microbial explanation for a striking purple rind defect in a surface-ripened cheese. A cheese producer in the United States reported to us several batches of a raw-milk washed-rind cheese with a distinctly purple rind. We isolated a Proteus species from samples with purple rind defect, but not from samples with typical rind pigments, suggesting that this strain of Proteus could be causing the defect. When provided tryptophan, a precursor in the indigo and indirubin biosynthesis pathway, the isolated strain of Proteus secreted purple-red pigments. A Psychrobacter species isolated from both purple and normal rinds also secreted purple-red pigments. Using thin-layer chromatography and liquid chromatography-mass spectrometry, we confirmed that these bacteria produced indigo and indirubin from tryptophan just as closely related bacteria make these compounds in purple urine bag sy...
Source: Food Microbiology - Category: Food Science Authors: Tags: Food Microbiol Source Type: research