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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Microbial and Chemical Food Safety » Research » Publications at this Location » Publication #276943
Title: The effect of acid stress on the growth of listeria monocytogenes and escherichia coli O157:H7 in cooked ham

Author
item Hwang, Cheng An
item HWANG, CHIN-FA - Hungkuang University
item YIN, TZU-CHIAO - Hungkuang University
item CHANG, NAI-YU - Hungkuang University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/9/2013
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Acid-based sanitizing solutions are increasingly being used for decontamination of processing equipment and food products. Microorganisms that survive acid decontamination may be subjected to acid stress that alters their growth characteristics. This study examined the growth of acid-stressed Listeria monocytogenes and Escherichia coli O157:H7 in a ham product. A mixture of five strains of each microorganism was incubated in HCl solutions of pH 3, 4, and 5 and distilled water (control) at room temperature for 24 h and inoculated onto cooked ham. L. monocytogenes- and E. coli O157:H7-inoculated samples were stored at 8 and 12 degrees Celsius, respectively. Populations of both microorganisms were enumerated during storage and the resulting growth curves were used to estimate the lag phase duration (LPD, h) and growth rate (GR, log/h). The acid treatments of pH 5, 4, and 3 solutions reduced the populations of L. monocytogenes and E. coli O157:H7 by 1.2-3.1 and 0.6-2.4 log cfu/ml, respectively, indicating an increased acid stress at lower pH. The LPD and GR of L. monocytogenes treated with pH 3 and 4 solutions were 72 and 70 h and 0.0227 and 0.0231 log /h, respectively, which were signficantly different from those treated with pH 5 (46 h and 0.0348 log/h) and control (26 h and 0.0359 log/g) solutions. The LPD and GR of E. coli O157:H7 treated with pH 3, 4, 5, and control solutions were 73, 70, 56 and 24 h and 0.0572, 0.0721, 0.0740, and 0.0761 log/h, respectively. Results indicated that acid stress extended LPD and reduced GR of both microorganisms, and the effect increased as the pH stress increased. Acid stress is likely to cause cell injury of L. monocytogenes and E. coli O157:H7 that leads to slow growth. Howerer, both microorganisms remain capable of growing at refrigerated abuse temperatures that warrants the need of proper temperature control.