Sixty-two samples of Pichtogalo Chanion cheese traditionally produced in Crete, a few (3 to 6) days old, were analyzed for some chemical and bacteriological characteristics. The results of physicochemical analyses were as follows: (1) moisture content 61.63% (standard deviation 4.67); (2) fat in dry matter 54.03% (SD 7.73); (3) protein content 14.23% (SD 1.72); (4) salt content 1.02% (SD 0.38); (5) water activity (aw) 0.990 (SD 0.003); and (6) pH 4.36 (SD 0.25). None of the samples yielded Salmonella spp. Listeria monocytogenes and coagulase-positive staphylococci were present in 6.45% of the samples. Bacillus cereus and sulfite-reducing clostridia were isolated from 14.51% and 40.32% of the samples, respectively. High populations of coliforms were determined in the cheese samples. In 11.3% of the samples, Escherichia coli was not detected, while 88.7% of the samples yielded E. coli most probable number levels from 1.32 to 5.66 log10/g. The log10 CFU/g counts of enterococci were 6.89 (SD 0.84), of yeasts 6.79 (SD 0.61), of molds 4.68 (SD 0.69), and of psychrotrophic bacteria 7.63 (SD 0.62). The log10 CFU/g counts of lactic acid streptococci and lactococci were 7.91 (SD 0.68) and of lactobacilli 8.11 (SD 0.65). Lactic acid bacteria, mainly mesophilic, were isolated and confirmed using API 50 CH test trips. A pasteurized mixture of ewe's and goat's milk was made into Pichtogalo Chanion cheese according to standard procedure at 23 degrees C, after the addition of 4% commercial mesophilic starter culture or 2%, 3%, and 4% starter culture of the isolated and confirmed lactic acid bacteria and the addition of rennet. Results of this work indicated that high quality of Pichtogalo Chanion cheese can be produced using a pasteurized mixture of ewe's and goat's milk and 4% (vol/vol) of mesophilic starter culture.
The fresh whey cheeses Myzithra, Anthotyros, and Manouri were inoculated with Listeria monocytogenes Scott A or California to contain ca. 5.0 × 102 CFU/g of cheese and incubated at 5, 12, and 22°C. The initial pH of the finished whey cheeses Myzithra, Anthotyros, and Manouri were 6.50, 6.41, and 6.30 respectively. Fat in dry matter was 16.3% in Myzithra, 65.9% in Anthotyros, and 71.7% in Manouri cheese; the moisture contents of the cheeses were 68.4, 66.9, and 52.2% respectively. The pH of the cheeses dropped gradually to between 5.30 to 4.97 during storage. Duplicate samples of whey cheeses were tested for numbers of L. monocytogenes and pH. Listeria counts were obtained by surface-plating on lithium chlorite-phenylethanol-moxalactam agar (LPM). Selected Listeria colonies were confirmed biochemically. The growth of L. monocytogenes in the whey cheeses was very rapid. Generation times of L. monocytogenes at 5°C ranged between 16.16 and 20.16 h and were significantly longer than those observed at 12°C, which ranged between 5.07 and 5.81 h. Generation times at 22°C ranged between 1.68 and 2.70 h. The generation time of L. monocytogenes Scott A at 5°C in Anthotyros cheese (20.16 h) was significantly longer than those of the same strain at 5°C in Myzithra cheese (16.16 h) and Manouri cheese (17.81 h). Also, the generation time of L. monocytogenes California at 22°C in Myzithra cheese (2.70 h) was significantly longer than the generation time of strain Scott A (1.93 h). Maximum populations of L. monocytogenes were reached after 24 to 30 days at 5°C, after 5 to 12 days at 12°C, and after only 56 to 72 h at 22°C and ranged from 6.92 to 8.81 log CPU/g. Maximum populations were significantly lower in Myzithra cheese at 5 and 12°C than maximum populations in Anthotyros and Manouri cheese at the same temperatures independent of the inoculated strain.
Pasteurized whole ewe's milk was inoculated to contain ca. 1.0 × 106 to 2.0 × 106 Listeria monocytogenes Scott A or California (CA). Inoculated milk samples of 200 ml in sterile stomacher bags were frozen at −38°C and stored at −18 or −38°C for 7.5 months. Inoculated milk was also made into Feta cheese curd, according to a standard procedure. After 5 h of drainage, curd samples of 200 g in sterile stomacher bags were frozen at −38°C, and stored at −18 or −38°C for 7.5 months. The pH values of the ewe's milk and Feta cheese curd before freezing were 6.70 and 5.43 respectively. At l5-day intervals samples were thawed at 35°C and tested for numbers of L. monocytogenes cells by surface plating on tryptose agar (TA) and tryptose salt agar (TSA) for ewe's milk samples, or on lithium chlorite phenylethanol moxalactam agar (LPMA) for curd samples. A high percentage (ca. 95%) of L. monocytogenes Scott A cells survived during storage of frozen ewe's milk at −18 or −38°C for 7.5 months. The population of L. monocytogenes CA decreased by ca. 50 and 40% during storage of frozen ewe's milk for 7.5 months at −18 and −38°C respectively. The death rate of L. monocytogenes increased after repeated freeze-thaw cycles of ewe's milk at −18 or −38°C. Populations of L. monocytogenes Scott A decreased by ca. 40% in the center of the cheese curd samples but the rate of death was less than ca. 17% on the surface of the frozen cheese curd samples during storage at −38°C for 7.5 months. Populations of strain Scott A decreased by ca. 57% in the center of the cheese curd samples and by ca. 22% on the surface of the frozen cheese curd samples during storage at −18°C for 7.5 months. Populations of L. monocytogenes CA decreased by ca. 98% for samples both at the center and the surface of the frozen curd during storage at −38 or −18°C for 7.5 months.
Soft spreadable cheeses Galotyri and Touloumotyri were inoculated with Listeria monocytogenes strains Scott A or California (CA), to contain 3.6-7.5 x 105 CFU/g of cheese and stored at 5°C and 12°C f or 30d and 40d respectively. The initial pH of the cheeses Galotyri and Touloumotyri were 4.35 (S.D.±0.08) and 4.53 (S.D. ±0.06) respectively, and remained relatively constant during the entire experiment. Fat in dry mater was 50.06% (S.D. ±1.16) in Calotyri and 37.43% (S.D. ±0.62) in Touloumotyri cheese. Values of moisture content of cheeses were 68.04% (S.D. ±0.36) and 73.01% (S.D.±0.14) respectively. The NaCl content for Galotyri and Touloumotyri cheeses was 1.54% (S.D.±0.12) and 1.03% (S.D. ±0.10) respectively. Duplicate samples of cheeses were used for enumeration of L. monocytogenes and pH. Listeria counts were obtained by surface plating on lithium chloride phenylethanol moxalactam agar (LPM). Selected Listeria colonies were confirmed biochemically. Viability loss of L. monocytogenes in Galotyri cheese was rapid, but the pathogen survived for more than 40 d in Touloumotyri cheese. During storage of Galotyri cheese at 5°C and 12°C, population of both strains of L. monocytogenes decreased significantly (P<0.01) to less than 10 viable cells/g of cheese, within 7 to 16 d for 7 trials. At that time population of L. monocytogenes decreased by 2.9-4.55 Log10 CFU/g. Estimated D-value was 2.17 d (S.D. ±1.02) for the 7 trials. Only for one trial L. monocytogenes was counted up to 24 d, but was not survived more than 26 d. The reduction of population was statistically significant (P<0.01) for this trial also. Cold enrichment up to 8 weeks of samples in which L. monocytogenes was not counted, indicated that the pathogen survived for 16 d up to 27 d in a l l trials. Both strains of L. monocytogenes survived for more than 40 d during storage of Touloumotyri cheese at 5°C and 12°C. Population of L. monocytogenes decreased significantly (P<0.05) by 0.98 to 1.96 Log10 CFU/g during storage of Touloumotyri cheese at 5 °C and 12 °C. After 40d of storage of cheese, populations of the pathogen ranged from 5.3 to 51 χΙΟ3 CFU/g. Calculation indicated that survivors of the pathogen represent the 1.1% up to 10.6% of the initial population of L. monocytogenes inoculated to the cheese.
In the present paper, the presence of Salmonella spp. in the egg-laying hens producing plants in Thessaloniki area was studied. In total, 2.230 eggshell samples, 588 samples surfaces from floor, walls, conveyor belts, utensils and packaging areas, 168 feed samples and 68 water samples were examined. The survey showed that the rate of contamination in the eggshells was 0.29-3.29% (mean value 1.65%). The contamination rate of the surrounding area of the cages (floor, walls, conveyor belts) and the surfaces in the packaging areas were 6.81% and 7.58% respectively. The feed was contaminated at a rate of 0-6.6% (mean value 4.2%), while all the water samples were free of Salmonella spp. Eighty-six strains of Salmonella were isolated belonging to the S. enteritidis serotype (76.8%), S. bredeney (20.29%) and S. Heidelberg (2,3%). The high prevalence of S. enteritidis, in contrast to the other serotypes, isolated from the eggshells, from the area of the egg producing plants and the feed, showed that strict preventive measures should be applied for the protection of public health and the avoidance of dispersion of Salmonella in the environment.
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