Bacillus cereus isolation, ribotyping and control in post-pasteurized milk / Isolamento, ribotipagem e controle de Bacillus cereus após a pasteurização do leite

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Bacillus cereus recontamination of post-pasteurized milk was assessed by product analysis and by previously sanitized surfaces analysis. The milk samples were collected during nine weeks and the surfaces of the packaging machine screw (PMS); of the packaging machine leveling tank (PMLT); of the package forming tube (PFT); of the packaging tube (PT), and of the pasteurized milk storage tank (PMST) were verified using surface swabs. Gram-positive were isolated on MYP and biochemically confirmed. The Bacillus cereus isolates were ribotyped and had their superficial electrical charge evaluated using electrostatic interaction chromatography. Furthermore, four different cleaning procedures to control bacterial adhesion to stainless steel surfaces were assessed. From 115 Bacillus sp. isolates, 35.65 % were from milk and 64.35 % were from stainless steel surfaces. Thirty isolates from surfaces and 12 isolates from milk were characterized as Bacillus cereus. Just after pasteurized milk packaging Bacillus sp. numbers varied from -0.349 log UFCmL-1 to 1.85 log UFCmL-1, with 0,588 log UFCmL-1 average. During the monitoring process, at the first and seventh weeks, the milk contamination reached or surpassed the upper control limit of 1.22 log UFCmL-1 (UCL). For the surfaces, the microbial numbers were between 0.061 log UFCcm-2 and 1,977 log UFCcm-2, with 0.646 log UFCcm-2. The Bacillus sp. contamination was out of control in the two first weeks practically for all studied surfaces after Standard Operational Procedures. The PMST showed a tendentious elevation and in the seventh week surpassed the UCL, standing out of control, indicating control and monitoring necessity at this critical point. After the statistical analysis, was verified a positive data autocorrelation, wich indicated the efficiency/deficiency of one week sterilization influenced the next week results for three surfaces. PMLT and PFT showed inconclusive results. The results showed a tendency, according to Durbin Watson test (P<0.05), during the weeks for PMS, PMLT, PMST surfaces, being the Bacillus sp. contamination predictable. Therefore, the monitoring process is important for the control, when the numbers start to rise. For the non tendentious surfaces, the monitoring is still important; the process could run out of control suddenly. Seven ribogroups were found and the same ribogroup was isolated from four surfaces and from pasteurized milk, what meant they were Bacillus cereus reservoirs. Only the PT was not associated with recontamination. The ribogroups were predominantly anionics (P<0.05) by F test. Analyzing the surfaces, microbial numbers after using different procedures, were verified that Bacillus cereus adhesion was affected by the alkaline solution temperature and concentration, by the use or not of acid solution and by chlorine solution pH. The industry must emphasize how to do the cleaning procedures and its performing, controlling the pH, the concentration, the temperature and the exposure time of the solutions. Also it is important how to assess for the process monitoring in order to corrective actions may be conducted when necessary.

ASSUNTO(S)

milk leite bacillus cereus quality qualidade bacillus cereus pcr ciencia de alimentos pcr

ACESSO AO ARTIGO

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