Traceability of pathogenic microorganisms along the pasteurized milk production: a potential tool for food safety

Author(s)

Natali Knorr Valadão

• Document type: Master's Dissertation
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
• Defense date: 2012-02-24

Examining board members

Carlos Augusto Fernandes de Oliveira; Adriano Gomes da Cruz; Marta Mitsui Kushida

• Advisor: Carlos Augusto Fernandes de Oliveira

Abstract

The aim of this study was to monitor the incidence of Staphylococcus aureus, Listeria sp., Listeria monocytogenes, Escherichia coli, total coliforms, mesophilic aerobic and psychrotrophic bacteria along the pasteurized milk production, from milking to the final product, to establish steps and critical points of production, as well as to evaluate the presence of Listeria sp. as a bioindicator of L. monocytogenes and E. coli a bioindicator of other pathogenic microorganisms. Duplicate samples were collected in 5 dairy plants (A, B, C, D, E) from the state of São Paulo, within intervals ranging from 3 weeks to 7 months, according to the dairy plants availability. A total of 236 samples were collected, being 36 of milk (raw and pasteurized), 162 from surfaces with no contact with the milk, and 38 from surfaces with contact with milk. Out of 36 milk samples analyzed, 13.9% were contaminated with Listeria sp. and none had L. monocytogenes; 61.1% were contaminated with E. coli and 5.6% with S. aureus. Only dairy plant C showed pathogenic microorganism (E. coli) in the pasteurized milk in one of the collections, indicating failures in the pasteurization or excessive bacterial load in the raw milk. Out of the 38 samples of surfaces that had contact with milk, 2.6% were positive for Listeria sp., 50.0% for E. coli and 5.3% for S. aureus. As for the samples from surfaces with no contact with milk (162), 13.3% were contaminated with Listeria sp., 6.2% with L. monocytogenes and 25.9% with E. coli. According to the Brazilian regulations for aerobic mesophiles in raw milk by Normative Instruction 62, 50.0% of samples from dairy plants A, D and E, 100% of samples from dairy plant B and 33.3% of samples from dairy plant C were above the tolerance limit adopted. The analysis of Listeria sp. could not be considered as a bioindicator of L. monocytogenes by chi-square test (p<0.05). When comparing the mean frequencies of positive samples for E. coli, S. aureus, Listeria sp. and L. monocytogenes in the processing dairy plants of type A milk (plants A and B) and the pasteurized one (plants C, D and E), only S. aureus in milk showed significant difference by \"T\" test (p<0.05). In addition to the critical control points (CCP) checked by a decision tree (pasteurization, internal surfaces of packaging), other points should be highlighted by the high number of pathogens found (bulk raw milk tanks, floors and walls of cold storage rooms). Results of this trial indicate the importance of adoption of quality management tools such as Good Manufacture Practices and HACCP, to ensure food safety along the pasteurized milk production chain in the dairy plants evaluated. (AU)

• FAPESP's process: 09/13377-0 - Rastreability of pathogens in dairy chain: potencial tool for food safety
• Grantee: Natali Knorr Valadão
• Support Opportunities: Scholarships in Brazil - Master