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

[摘要] 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 B:1A, O: 3,50,51; lis Xz, while the other one was biotyped as: B:1A 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 -18°C 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 combination 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 findings suggest that the survival time of Y. enterocolitica in ice cream stored at -18°C is significantly (p <= 0,05) lower at pH values under 5.

[关键词] Yersinia;isolation;survival;ice cream;pH;Yersinia;isolamento;sobrevivência;sorvetes;pH