Role of Thermoduric and Thermophilic Sporeformers and Their Biofilms in Cheese Spoilage

Thermophilic and thermoduric sporeforming bacteria can survive milk pasteurization and resist the chemicals used in general cleaning and sanitation protocols. These organisms have the ability to grow at relatively higher temperatures and produce thermostable enzymes that cause cheese defects such as bitterness, unclean flavor, phenolic flavor, late blowing of cheese, and produce biogenic amines. The regeneration section of pasteurization, hot membranes processing for milk concentration, hot holding retentate tanks prior to renetting, and starter addition are some critical spots that can support the development of bacterial biofilms. Bacillus, Paenibacillus, Micrococcus, Clostridium, Anoxibacillus, Microbactyerium are some of the prominent bacteria involved in forming these resistant biofilms. </P>The objective of this project was to study the progression of thermophilic and thermoduric sporeformers during cheese making and whey processing and develop mechanisms to control undesirable biochemical changes that occur during ripening and storage. Thermoduric and thermophilic sporeformers, and their biofilms, were screened at milk reception, processing, and whey processing stages in commercial cheese plants. Researchers identified 260 thermoduric isolates from their studies on species progression, biofilms, and spoiled cheese. Over 96% of the isolates were from the genus Bacillus, which included 73% Bacillus licheniformis, 17% Bacillus subtilis and 5% Bacillus cereus. The predominant contaminant that survived cheese making and persisted in the final cheese curd was B. licheniformis. Environmental samples were positive for B. licheniformis, B. subtilis, and B. cereus. The major gas producing isolates that caused slit defects in cheese were Lb. fermentum and Clostridium beijerinckii.