Hot Topic: Black Spot Defect in Cheddar Cheese Linked to Intramammary Teat Sealant

• Published in: Journal of dairy science Vol. 90; no. 11; pp. 4938 - 4941
• Main Authors: Lay, A.M., Kolpin, K.M., Sommer, D.A., Rankin, S.A.
• Format: Journal Article
• Language: English
• Published: Savoy, IL Elsevier Inc 01.11.2007; American Dairy Science Association; Am Dairy Sci Assoc
• Subjects: animal husbandry; Animal productions; Animals; Anti-Bacterial Agents - analysis; Anti-Bacterial Agents - metabolism; Biological and medical sciences; bismuth; Bismuth - analysis; Bismuth - metabolism; black spot; black spot defect; Cattle; Cheddar; Cheddar cheese; cheese; Cheese - analysis; Cheese - standards; cheese ripening; chemical composition; dairy cows; Dairying - methods; diameter; etiology; Female; Food industries; food quality; Fundamental and applied biological sciences. Psychology; hydrogen sulfide; Hydrogen Sulfide - metabolism; Mammary Glands, Animal; Metals - analysis; Milk and cheese industries. Ice creams; Nitrites - analysis; Nitrites - metabolism; quality defects; salts; teat sealant; teat sealants; teats; Terrestrial animal productions; transmission electron microscopy; Vertebrates; teat sealant; black spot; Cheddar; cheese; Teat; Dairy industry; Dairy product; Defect; Cheese
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2007-0385

The objective of this work was to characterize a novel appearance defect found in Cheddar cheese, heretofore referred to as black spot defect (BSD), and to determine an etiology. Uniformly distributed throughout the cheese mass, BSD appears as small spherical black spots from 0.20 to 4.7mm in diameter and at an average frequency of about 2 spots per kg of cheese. To date, BSD has only been found in aged Cheddar cheese. Selected elemental analysis found the BSD region in cheese to have average concentrations of the element bismuth of approximately 400μg/g, representing an approximately 2,500-fold increase over native levels of bismuth in cheese. Transmission electron microscopy analysis of the BSD region revealed amorphous solid structures and one-dimensional hair-like structures, neither of which was present in non-BSD regions. Such amorphous “nanorod” structures can be formed by the crystallization of bismuth III sulfide and are proposed to be a source of black discoloration. We hypothesize that localized bismuth salts entrained within the cheese curd react with hydrogen sulfide generated during aging to generate bismuth III sulfide. We further propose that the presence of localized bismuth salt precursor results from residual levels of a commercial intra-mammary teat sealant containing bismuth subnitrate that becomes unintentionally entrained within the cheese milk.