Isolation and survival of "Yersinia enterocolitica" in ice cream at different pH values, stored at -18ºC

RESUMO

The presence of "Yersinia enterocolitica" was investigated in 203 samples of industrial (123) and non-industrial ice cream (80). Two "Y. enterocolitica" strains were isolated from non-industrial ice cream, which suggests the possibility of post-manufacturing contamination. One strain was typed as B1A, O3,50,51; lis Xz, while the other one was biotyped as B1A but not serologically typed. Survival of "Y. enterocolitica" was investigated by inoculating nine samples of industrially manufactured ice cream to contain 20 CFU/ml of "Y. enterocolitica" and stored at -18ºC for 480 days. The inoculated samples were classified into three different groups according to their pH (Group 1 pH 4-5; Group 2 pH 5-6 and Group 3 pH 6-7). Viability was determined by a contamination of direct plating and enrichment. In Group 1, "Y. enterocolitica" was not detected after 150 days of storage, while in Groups 2 and 3, this microorganism was isolated until day 480 of storage. These fidings suggest that the survival time of "Y. enterocolitica" in ice cream stored at -18ºC is significantly (p<=0.05) lower at pH values under 5.