Abstract
Microbial damages caused by biofilm forming bacteria in the dairy industry are a fundamental threat to safety and quality of dairy products. In order to ensure the optimal level of equipment hygiene in the dairy industry, it is necessary to determine the biofilm removal efficiency of cleaning agents used for cleaning-in-place (CIP) procedures. However, currently there is no standard method available for evaluating and comparing cleaning agents for use in CIP procedures in the dairy industry under realistic conditions. The present study aims to establish a CIP model system to evaluate the effectiveness of cleaning agents in removal of biofilm derived spores from the surfaces of stainless steel which is the predominant substrate in milking equipment on dairy farms. The system is based on Bacillus subtilis spores surrounded with exopolymeric substances produced by bacteria during biofilm formation. The spores applied on sampling plates were mounted on T-junctions protruding 1.5–11-times the milk pipe diameter from the main loop to resemble different levels of cleaning difficulty. The cleaning tests were conducted using commercial alkaline detergents and caustic soda at conditions which are relevant to actual farm environment. The spores removal effect was evaluated by comparing the number of viable spores (attached to sampling plates) before and after cleaning. Evaluation of the cleaning and disinfecting effect of cleaning agents toward biofilm derived spores was further performed, which indicates whether spores elimination effect of an agent is due to killing the spores or removing them from the surfaces of dairy equipment. Moreover, it was established that the presence of extracellular matrix is an important factor responsible for high level of cleaning difficulty characteristic for surface attached spores. In overall, the results of this study suggest that the developed model system simulates actual farm conditions for quantitative evaluation of the effectiveness of cleaning and disinfecting agents and their cleaning and disinfecting effect on removal of biofilm derived spores.
Highlights
Bacterial contamination can adversely affect the quality, functionality, and safety of dairy products
In order to simulate biofilm derived spores, we have developed the system that is based on B. subtilis spores surrounded with exopolymeric substances produced by bacteria during biofilm formation
To confirm the high level production of extracellular matrix in the biofilm colonies, we analyzed the level of the matrix gene expression in LBGM using transcriptional fusion of the promoter for tapA-sipW-tasA to the cfp gene encoding cyan fluorescent protein (Chai et al, 2008) as described previously (Shemesh et al, 2010)
Summary
Bacterial contamination can adversely affect the quality, functionality, and safety of dairy products. It appears that the major source of the contamination of dairy products is often associated with biofilms on the surfaces of dairy processing equipment (Flint et al, 1997; Sharma and Anand, 2002a). The persistence of accumulated microorganisms in the form of biofilms on dairy equipment causes pre- and post-processing contamination, leading to lowered shelf-life of products and possible transmission of diseases (Faille et al, 2002; Sharma and Anand, 2002b; Shaheen et al, 2010). Biofilms are a potential source of contamination, but can increase corrosion rate of metal pipes and equipment often used in the dairy industry, reduce heat transfer and increase fluid frictional resistance (Kumar and Anand, 1998). It becomes increasingly clear that bacterial biofilms are a major concern to modern dairy industry; especially with current trends toward longer production runs, the use of complex equipment, the automation of plants and increasingly stringent microbiological requirements
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