Pink discoloration in cheese is a defect affecting many cheeses throughout the world, leading to significant financial loss for the dairy industry. Despite decades of research, the cause of this defect has remained elusive. The advent of high-throughput, next-generation sequencing has revolutionized the field of food microbiology and, with respect to this study, provided a means of testing a possible microbial basis for this defect. In this study, a combined 16S rRNA, whole-genome sequencing, and quantitative PCR approach was taken. This resulted in the identification of Thermus, a carotenoid-producing thermophile, in defect-associated cheeses and the recreation of the problem in cheeses to which Thermus was added. This finding has the potential to lead to new strategies to eliminate this defect, and our method represents an approach that can be employed to investigate the role of microbes in other food defects of unknown origin.

-Split and secondary fermentation defects in Swiss-type cheese varieties are manifested as undesirable slits or cracks that may lead to downgrading of the cheese. Split defect is associated with an excessive production of gas or an unsuitable cheese body that cannot accommodate gas produced, or a combination of both factors. Secondary fermentation is the apparent production of gas after the desired propionic fermentation of the warm room has taken place. No consensus exists as to the definitive causes of the defects, but possible causes are reviewed under factors that are associated with rheological behaviour (including cheese manufacture, acidification, intact protein content and proteolysis, seasonality of milk supply and ripening or storage temperature and duration) or with overproduction of gas (including milk microflora, propionic acid bacteria (PAB) -in particular strains with high aspartase activity and ability to grow at low temperatures, lactic acid bacteria, interactions between starter bacteria, facultatively heterofermentative lactobacilli (FHL) and other sources of gas including butyric acid fermentation). The influence of other parameters such as copper concentration, air incorporation, salt content, rind formation and cheese wrapping materials is also considered. Methods to reduce the prevalence of the split defect and secondary fermentation include addition of water to improve elastic properties by the removal of unfermented carbohydrate and the use of FHL to control PAB activity to prevent the production of excessive gas.Swiss-type cheese / split defect / secondary fermentation / eye formation Article published by EDP Sciences Résumé -Défaut de lainure et fermentation secondaire des fromages à pâte pressée cuiteune revue. Les défauts de lainure et de fermentation secondaire des variétés de fromage à pâte pressée cuite se manifestent sous forme de fentes ou fissures qui peuvent entraîner le déclassement du fromage. Le défaut de lainure est associé à une production excessive de gaz ou à une pâte fromagère inadaptée pour contenir le gaz produit, ou à une combinaison des deux facteurs. La fermentation secondaire est la production apparente de gaz après que la fermentation propionique désirée dans la cave chaude ait eu lieu. Il n'existe pas de consensus sur les causes définitives de ces défauts, mais des causes possibles sont présentées au regard de facteurs associés au comportement rhéologique (incluant la fabrication fromagère, l'acidification, la teneur en protéines intactes et la protéolyse, la saisonnalité de l'approvisionnement de lait, et la température et la durée de l'affinage et du stockage) ou associés à la surproduction de gaz (incluant la microflore du lait, les bactéries propioniques, en particulier les souches ayant une activité aspartase élevée et l'aptitude à croître à basses températures, les bactéries lactiques, les interactions entre les bactéries du levain, les lactobacilles hétérofermentaires facultatifs et d'autres sources de gaz incluant la fermentation butyrique). L'...

Development of a pink color defect is an intermittent but persistent defect in a wide range of ripened cheese varieties (Swiss, Cheddar, Grana, and Italian types) which may or may not contain an added colorant, e.g., annatto. Pink discoloration results in downgrading or rejection of a product with consequential economic loss to producers. Pink discolorations can manifest in a number of ways, e.g., patches at the surface or within the cheese block, or as a uniform pink border occurring below the surface of cheese blocks. Little consensus exists as to what the discolorations and their underlying causes are. This review seeks to provide an overview and interpretation of the underlying factors associated with the defect for both research and commercial audiences. In cheeses without added colorant, pink discoloration has been associated with: certain strains of thermophilic lactobacilli and propionic acid bacteria, Maillard reactions, and microbial pigments (e.g., carotenoids and phenolic compounds), which may be responsible for development of pink-brown or dark brown discoloration. In cheeses with added colorant (usually annatto), the development of pink discoloration has been associated with: alteration of annatto colorant due to factors such as varying pH levels within the cheese matrix (particularly < pH 5.4), oxidation of bixin in storage under high intensity fluorescent lights in display cabinets, presence of oxygen, variations in redox potential, interactions between nitrates and annatto present in plastic surface coating and also due to interactions between colorants, and the use of high heat treatment during processed cheese manufacture.