Abstract
The changes of microbial flora and some chemical characteristics (pH, % moisture and % salt-in-moisture) in Batzos, raw goat’s milk cheese, were studied during ripening, throughout the whole lactation season in nine cheese batches manufactured three in each, winter, spring and summer. High counts of Enterobacteriaceae and coliforms were recorded early in ripening, but their levels decreased significantly (P<0.05) on ripening and storage. Lactic acid bacteria predominated over the other microbial groups throughout ripening, during the whole lactation season. It seems possible, that high NaCl content of the cheese was the main agent that regulated the microbial survival. No significant differences were observed in the counts related to the season when the cheeses were ripened and stored. However, the season affected the composition of the lactic microflora. Thus, in winter enterococci were abundant, while in spring and summer lactobacilli isolates were found more frequently. The main Ent ...
The changes of microbial flora and some chemical characteristics (pH, % moisture and % salt-in-moisture) in Batzos, raw goat’s milk cheese, were studied during ripening, throughout the whole lactation season in nine cheese batches manufactured three in each, winter, spring and summer. High counts of Enterobacteriaceae and coliforms were recorded early in ripening, but their levels decreased significantly (P<0.05) on ripening and storage. Lactic acid bacteria predominated over the other microbial groups throughout ripening, during the whole lactation season. It seems possible, that high NaCl content of the cheese was the main agent that regulated the microbial survival. No significant differences were observed in the counts related to the season when the cheeses were ripened and stored. However, the season affected the composition of the lactic microflora. Thus, in winter enterococci were abundant, while in spring and summer lactobacilli isolates were found more frequently. The main Enterococcus species was Ent. durans while among Lactobacillus, were Lb. plantarum and Lb. paraplantarum. Lactococcus lactis subsp lactis was the most frequently isolated species in the cheese and its use as starter seems promising.During the second experimental phase, the genotypic and phenotypic variability of 40 Lactococcus lactis isolates obtained from three cheese-making trials of Batzos cheese made one in each, winter, spring and summer was investigated, in order to find the appropriate culture for the production of Batzos cheese. The genotypic and phenotypic heterogeneity of the lactococcal isolates was investigated. RAPD-PCR, plasmid profiling and PFGE were used to study the genetic variability and distinguish closely related isolates. Results showed a high degree of heterogeneity among strains. According to PFGE data, all strains except one were clustered together (at a similarity level of ~50%) with the L. lactis subsp. lactis reference strain and eleven groups of isolates consisting of 2-8 strains each were distinguished. Plasmid profiling results revealed that there were eight isolates lacking plasmids and nine having unique plasmids. Twenty-three isolates were allocated into six groups. There was an interesting similarity between the plasmid profiling groups and those formed according to PFGE. Clustering of strains according to RAPD-PCR was in agreement with results obtained by both plasmid profiling and PFGE for the majority of the strains. In addition, results obtained by molecular methods indicate a grouping of most of the strains according to the season of cheese production. All strains inhibited the growth of E.coli O157:H7. Their ability to affect the growth of Y.enterocolitica, S.aureus, B.cereus, L.monocytogenes and E.faecalis was strain dependent. In 42.5% of the isolates high acidifying ability in milk after 24h was recorded and these were isolates, mainly, from fresh cheese. The 75% of the isolates from winter cheese exhibited higher Lys- than Leu- aminopeptidase activity while the ~67% of the isolates from summer cheese showed higher Leu- than Lys- aminopeptidase activity. Their caseinolytic activity after growth in milk for 24h was significant with preference for αs-casein degradation. The majority (90%) of the strains formed methanethiol from methionine and this ability was strain dependent. These results suggest that among the wild lactococcal population from Batzos cheese there are interesting strains appropriate to be used as starters for the dairy industry. Due to the high levels of enterococci in Batzos cheese, during the third phase of our investigation, the genotypic and phenotypic diversity in 34 isolates of enterococci obtained during ripening of Batzos cheese from raw goat milk and characterized phenotypically as Enterococcus durans, was studied, in order to investigate their contribution to the organoleptic characteristics of Batzos cheese and study their genotypic and phenotypic heterogeneity. RAPD-PCR, plasmid profiling and PFGE were used to study the genetic variability and distinguish closely related isolates. Species recognition by means of RAPD-PCR was in agreement with the phenotypic identification for 29 strains. One strain was characterized as Lactococcus lactis subsp lactis by RAPD-PCR and four strains were grouped with the Enterococcus faecium reference strain. All strains were vancomycin sensitive, while 10 strains showed β-haemolytic reaction on human blood and the majority of them (88.9%) showed decarboxylase activity on tyrosine. All strains exhibited antagonistic activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli and Listeria monocytogenes and the majority inhibited Enterococcus faecalis.
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