Med. Weter. 74 (9), 591-598, 2018

full text

Variability of microbial contamination of edible snail meat depending on species and place of their collection
The objective of the research was to determine the microbiological status of raw and frozen (cooked) snail meat obtained from both free-living and farmed edible snails. The research material comprised meat samples (10 g each) collected from three snail species, i.e. Roman snail (Helix pomatia – HP), small brown garden snail (Cornu aspersum aspersum – CAA) and large brown garden snail (Cornu aspersum maxima – CAM). Roman snails were collected in their natural environment in Greater Poland Voivodeship (region A: HPA) and Lower Silesian Voivodeship (region B: HPB). The Cornu genus snails were obtained from two different heliciculture farms in Greater Poland Voivodeship (farm A: CAAA and CAMA) and Lower Silesian Voivodeship (farm B: CAAB and CAMB). In both farms, snails were maintained under the mixed rearing system. Raw meat samples, taken from the edible portion of snails, that is, the foot with the collar and a fragment of the mantle, were obtained after the snails had been sacrificed in the laboratory. Frozen meat samples came from a snail meat processing facility. The samples were analyzed to determine the total bacterial count and the counts of Enterobacteriaceae, Escherichia coli, Enterococcus, Staphylococcus, Pseudomonas and Aeromonas, as well as psychotropic and proteolytic bacteria counts. Proteolytic bacteria were counted according to appropriate methodology, whereas the counts of other groups of microorganisms were obtained in accordance with the Polish Standards. Bacterial contamination levels (expressed as log cfu/g) were analyzed using the Statistica software (version 10.0). All values are presented as means and standard deviations. The total aerobic bacteria counts for HPA, HPB, CAAA, CAMA, CAAB and CAMB samples were, respectively, 5.78, 5.10, 6.00, 6.55, 5.12 and 5.21 log cfu/g in the case of raw meat, and 4.59, 4.75, 4.60, 5.13, 4.25 and 4.68 log cfu/g in the case of frozen meat. It was found that bacteria from the Enterobacteriaceae family were prevalent in both raw and frozen snail meat. The percentage of contaminated samples oscillated between 73.3% (HPB and CAMB) and 96.7% (CAAA and CAAB) for raw meat and between 20% (CAAA) and 100% (CAMA) for frozen meat. The quantitative contamination of raw meat with Enterobacteriaceae varied from 2.54 (HPB) to 4.75 log cfu/g (CAAA) and was higher by 1.0 to almost 2.0 log in farm snail meat as compared to Roman snail meat. The quantitative contamination of frozen meat was lower, ranging from 0.5 (HPA, CAAA and CAMA) to 1.65 log cfu/g (CAMB). All samples of raw and frozen snail meat were free from E. coli (contamination below 1 log cfu/g).
In the raw snail meat, enterococci were recovered from 3 (10%) HPA, 6 (20%) HPB, 9 (30%) CAAA, 18 (60%) CAMA, 6 (20%) CAAB and 17 (56.6%) CAMB samples. The contamination levels for HPA, HPB, CAAA, CAMA, CAAB and CAMB raw meat samples were, respectively, 0.3, 0.63, 0.42, 2.0, 0.66 and 1.57 log cfu/g. In the frozen snail meat, enterococci were detected in 13 (43.3%) HPA, 13 (43.3%) HPB, 6 (20%) CAAA, 16 (53.3%) CAMA, 1 (3.3%) CAAB and 10 (30%) CAMB samples. The contamination level was similar for all kinds of samples, ranging between 0.48 (CAAA) and 2.11 log cfu/g (CAMA). The percentages of raw and frozen meat samples contaminated with staphylococci were similar, ranging from 50% (HPA) to 86.7% (CAMA) for raw meat and from 50% (HPA) to 100% (CAAA, CAMA and CAMB) for frozen meat. Quantitative contamination levels were also similar, oscillating between 1.48 (HPA) and 2.84 log cfu/g (CAMB) for raw meat and between 1.89 (HPA) and 3.28 log cfu/g (CAMA) for frozen meat. The percentage of samples contaminated with psychotropic bacteria was also similar for raw and frozen snail meat, varying from 90% to 100%. Quantitative contamination with these bacteria oscillated between 3.17 (HPB) and 5.53 log cfu/g (CAMA) for raw meat and between 2.95 (HPA) and 4.12 log cfu/g (CAMA) for frozen meat. Bacteria from the Pseudomonas genus were confirmed in 63.3% of raw meat samples, in which the contamination level ranged from 2.22 (HPA) to 4.15 log cfu/g (CAAA), and in 96.7% of frozen meat samples, which contained from 1.12 (CAMA) to 2.21 log cfu/g (HPB) of these microorganisms. In raw meat, bacteria from Aeromonas genus were identified in all HPA samples as well as in 29 (96.7%) HPB, 26 (86.7%) CAAA, 21 (70%) CAMA, 29 (96.7%) CAAB and 17 (56.7%) CAMB samples. These bacteria were also present in a similar proportion of frozen meat samples (46.7-100%). The contamination level for raw meat samples oscillated between 2.74 (CAMB) and 4.73 log cfu/g (CAAA), whereas for frozen meat samples, it was substantially lower, ranging between 1.14 (CAMA) and 2.58 log cfu/g (CAAB). Proteolytic microbes were isolated more frequently from frozen snail meat. The percentage of contaminated samples varied from 80% (HPB and CAAA) to 100% (the rest) for frozen meat and from 36.7% (CAMA) to 93.3% (CAMB) for raw meat. The quantitative contamination level for frozen meat ranged from 3.17 (CAAA) to 4.44 log cfu/g (CAMA) and was generally lower than in the raw meat, where it varied between 2.07 (HPA) and 4.90 log cfu/g (CAMA). Snail meat is characterized by a high level of total microbiological contamination. The species of snails and the place where they live are often significant factors determining the level of contamination, which is higher in farm snail meat than in Roman snail meat. Heat treatment reduced the counts of bacteria found in raw meat. The increase in the number of staphylococci and enterococci in frozen meat (statistically significant only for staphylococci in snail meat from farm A) suggests the possibility of a secondary contamination of heat-treated meat. Therefore, a necessary condition for obtaining a safe and durable product is absolute compliance by the staff with appropriate procedures for hand hygiene and proper handling of food during production.
Key words: Cornu genus, Helix pomatia, snail meat, microbiological contamination