Dott. Marco Loguercio
Technical consultant
Alpha Solutions, Food and Ingredients
mlo@alpha-solutions.it
Source: John Haldemann, Agroscope.
Recently, Swiss cheese experienced the so-called black spot defect. After several reportings from cheese pre-packaging operators, Agroscope, the Swiss Centre of excellence for agricultural research affiliated with the Federal Office for Agriculture (FOAG), was able to clarify the cause of such defect in cheese.
The results of the analyses conducted by Agroscope showed that the compound causing black spots is bismuth, the main component of teat sealants (veterinary medicines used to dry-off cows).
Bismuth residues were detected in milk samples and in milking facilities. Teat sealants generate deposits in teat liners, milking lines and cleaning machines. Removal of bismuth residues from milking equipment is difficult, despite the temperature, concentration and cleaning agent used in cleaning procedures.
Agroscope recommended some good management practices to milk suppliers to avoid the black spot defect in cheese. The recommendations are available here.
Agroscope confirmed that cheese organizations tried to solve the issue. For instance, Gruyère Switzerland AOP and Etivaz AOP banned the use of bismuth using the bismuth teat sealants.
The presence of black spots appeared to be a major challenge in matured cheese wheels.
How can the formation of such black spots from bismuth be explained?
In 2007, Lay and colleagues* tried to give an answer to this question. At the time, the defect had only been identified in aged Cheddar cheese.
The authors conducted a transmission electron microscopy analysis of the black spots in the cheese, which revealed amorphous solid structures and single-dimension hair-like structures.
The authors explained these amorphous “nanorod” structures to be formed through the crystallization of bismuth III sulfide, suggesting a source of black discoloration. They also hypothesized that bismuth salts dispersed within the curd react with hydrogen sulfide released during aging to form bismuth III sulfide. They further proposed that the origin source of bismuth was the unintentional contamination of commercial intra-mammary teat sealants containing bismuth subnitrate.
Find out more about the black spot defect at the following links:
https://www.dairyindustries.com/news/40342/black-spots-on-cheese-solved-in-switzerland/
* A. M. Lay, K. M. Kolpin, D. A. Sommer, and S. A. Rankin. Hot Topic: Black Spot Defect in Cheddar Cheese Linked to Intramammary Teat Sealant. J. Dairy Sci. 90:4938–4941 doi: 10.3168/jds.2007-0385