Heat resistance of Yersinia enterocolitica grown at different temperatures and heated in different media.
In the range of 4-20 degrees C, growth temperature did not influence the heat resistance at 54-66 degrees C for Yersinia enterocolitica at pH 7 in citrate phosphate buffer. However, when cells were grown at 37 degrees C. the D62 increased from 0.044 to 0.17 min. This increase was constant at all heating temperatures tested (z = 5.7-5.8). Growth temperature did not influence the proportion of heat-damaged cells after a heat treatment, as measured by their response to a 2% of sodium chloride added to the recovery medium. The sensitivity of heat treated cells to nisin or lysozyme depended on growth temperature: Whereas the number of cells grown at 4 degrees C surviving heat treatment was the same regardless of the presence of 100 IU/ml of nisin or 100 microg/ml of lysozyme in the recovery medium, that of cells grown at 37 degrees C was, in these media, lower. The pH of maximum heat resistance in citrate phosphate buffer was pH 7 for cells grown at 37 degrees C, but pH 5 for those grown at 4 degrees C. In both suspensions the magnitude of the effect of pH on heat resistance was constant at all heating temperatures. For cells grown at 4 degrees C the heat resistance at 54-66 degrees C, in skimmed milk or pH 7 buffer, was the same. For cells grown at 37 degrees C this also applied for heat treatment at 66 degrees C but at 56 degrees C the heat resistance in skimmed milk was higher.
Pagán
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Dpto. P.A.C.A.-Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, Spain.
Mañas
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P
Raso
J
J
Trepat
F J
FJ
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002417:Cattle; D015169:Colony Count, Microbial; D003470:Culture Media; D005516:Food Microbiology; D005520:Food Preservatives / Q000494:pharmacology; D006358:Hot Temperature; D007091:Image Processing, Computer-Assisted; D008892:Milk; D009113:Muramidase / Q000494:pharmacology; D009561:Nisin / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D015009:Yersinia Infections / Q000517:prevention & control; D015008:Yersinia enterocolitica / Q000187:drug effects / Q000254:growth & development*
D000900:Anti-Bacterial Agents; D003470:Culture Media; D005520:Food Preservatives; D009561:Nisin; D012965:Sodium Chloride; D009113:Muramidase