Estudo de perigos biológicos presentes na superfície de frutos de casca rija e nas folhas de produtos frescos

Abstract

Fruits and vegetables eaten raw are potential vehicles of pathogens due to the impossibility of applying thermal treatments, which would considerably reduce biological hazards that might be present. Lettuce is one of the most consumed salad vegetables in Portugal and absorption of nutrients is favoured by the consumption of raw leaves, which remain uncovered from production to the distribution phase. Fruits have a physical barrier, the peel, which protects them from microbial contamination and proliferation. However, many fruits possess rough peels and very pronounced textures that can contribute to a significant increase in microbial load transported and therefore result in contamination of the interior of the fruit during peeling. The aim of this study was to evaluate the microbial load on the surface of fruits with rough and very pronounced textured peels, namely pineapples and melons, as well as leaf lettuce, analyzing the varieties, countries of origin and distribution sites of these products. Enumeration of total microorganisms, Enterobacteriaceae, Escherichia coli and coagulase-positive staphylococci, as well as detection of Listeria monocytogenes and Salmonella spp., were performed for all samples. Significant differences were observed in lettuce samples according to distribution sites: samples purchased at supermarkets showed lower E. coli counts than those of other establishments. Faecal contamination was found in 47.5 % of lettuce samples and 15 % were contaminated with L. monocytogenes. Significant differences were observed in fruit peels according to country of origin and distribution sites. Pineapples from Ecuador and melons from Morocco had higher total microorganism and Enterobacteriaceae counts, respectively, than other countries. The fruits purchased in hypermarkets showed lower bacterial counts when compared with other establishments. 5 % of pineapples presented faecal contamination and 2.5 % were contaminated with L. monocytogenes. Melon samples were negative for E. coli, L. monocytogenes and coagulase-positive staphylococci. L. monocytogenes isolates belonged to serogroups 2 (1/2c or 3c) or 4 (4b, 4d and 4e) and none were found to be resistant to antibiotics commonly used in therapy of listeriosis. All coagulase-positive staphylococci had similar characteristics and none exhibited multidrug resistance. Salmonella spp. was not detected in fruits and vegetables analyzed in this study.

Date of Award	8 Nov 2011
Original language	Portuguese
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Paula Teixeira (Supervisor) & Joana Silva (Co-Supervisor)