Pink discoloration defects associated with microbial structure and metabolome changes in commercial bloomy cheeses

This study investigates pink discoloration defects in French bloomy rind soft cheeses, which can negatively affect product appearance, consumer acceptance, and lead to economic losses. Two batches of cheese from the same processing plant were analyzed: one with visible pink discoloration and one without, allowing for comparative analysis. A multi-omics approach was applied, combining microbial profiling (16S rRNA and ITS2 sequencing) and metabolomics (GC-MS and LC-MS) to identify the factors linked to the defect. Three microbial species showed significant differences in abundance depending on sample type (spoiled and unspoiled) and location on the cheese surface: Penicillium camemberti, Psychrobacter group, and Paeniglutamicibacter gangotriensis. A positive correlation was observed between this group and salt concentration, as well as with multiple metabolites such as butanoic acid, acetic acid, aldehydes, ketones, esters, and terpenes. Notably, P. gangotriensis had never previously been detected in cheese. To test its role, model cheeses were inoculated with or without six strains of P. gangotriensis isolated from cheeses. Model cheeses containing the bacteria developed pink discoloration after 14 days of ripening, while controls remained unchanged after 20 days. These results strongly suggest that P. gangotriensis is responsible for the pink defect. Further research is needed to confirm this hypothesis by identifying the pigment's chemical structure and understanding the biotic and abiotic conditions that promote its production.