Microbial contamination of luncheon meat sliced and packaged at supermarkets in Porto Alegre, Brazil

Abstract

Background: Ready-to-eat (RTE) foods are considered a high risk food group, since they are often consumed without a cooking step. Luncheon meat, a RTE food widely consumed in Brazil, is traditionally produced as industrially vacuum-packaged loaves and afterwards is sliced and re-packaged at retail stores. Since this practice may pose an additional hazard of contamination, the purpose of this study was to evaluate total coliform counts (TCC), coagulase-positive staphylococci counts (CPS), and the occurrence of Escherichia coli and Listeria sp. in luncheon meat samples sliced and packaged at supermarkets. Materials, Methods & Results: Three supermarket stores belonging to either regional or national chains located in Porto Alegre were intentionally chosen, and luncheon meat samples were purchased from the same sampled stores weekly during a 20-week period. In each sampling event, five store-packaged luncheon meat samples were obtained and analyzed. Individual samples (25 g) were homogenized, decimally diluted in buffered peptone water and submitted to TCC in Violet Red Bile Agar. Thermotolerant coliform (FC) were confirmed in EC broth incubated at 45°C. Confirmed tubes were streaked on McConkey agar and submitted to E.coli identification. Isolation and enumeration of coagulase-positive staphylococci (CPS) were performed on Baird-Parker agar. The presence of Listeria sp. was tested in pooled samples submitted to pre-enrichment in University of Vermont (UVM) Listeria Enrichment broth, followed by incubation in Fraser broth and isolation on tryptose agar with nalidixic acid and Palcam agar. TCC mean varied from 1.2 log10 CFU.g-1 (store B) to 5.5 log10 CFU.g-1 (store C), while CPS mean counts were similar (0.63; 0.65 and 0.86 log10 CFU.g-1) for samples purchased at the three stores. Considering Brazilian standards for FCC, in stores A (n=6) and C (n=8) samples considered unsafe (above 3log. g-1) were found, while all samples purchased at store B are considered sound according to that standard. Moreover, three samples from each store (A and C) confirmed for the presence of E. coli. Samples contaminated with Listeria sp. (n=16) were also found. Listeria monocytogenes was isolated from six samples, and was found in all sampled supermarkets. A trend of Listeria sp. isolation frequency in samples with higher TCC was observed. Discussion: The results demonstrated that bacteria may be introduced in luncheon meat during the slicing and packaging at supermarkets. Our data are in accordance with other reports that indicate slicing as a critical control point of contamination and transfer of pathogen, including L. monocytogenes, to foods during processing. Differences observed on extend of product contamination may have resulted from variable levels of cleanliness during handling and slicing procedures at the three supermarkets. Specifically, the cleaning of equipment surfaces represents a challenge for sanitation programs, since most equipment is not hygienically designed and must be unassembled prior to sanitization procedures. This fact may lead to the decrease of cleaning and disinfection frequency and to the hazard of biofilm formation. In conclusion, luncheon meat sliced and packaged in supermarkets may pose a hazard to the consumers, and the adoption of more rigorous disinfection protocols for equipment and surfaces in contact with ready-to-eat foods in these stores is advisable.