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Applied and Environmental Microbiology, December 2008, p. 7570-7577, Vol. 74, No. 24
0099-2240/08/$08.00+0     doi:10.1128/AEM.00936-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Relationship between Sublethal Injury and Microbial Inactivation by the Combination of High Hydrostatic Pressure and Citral or tert-Butyl Hydroquinone {triangledown}

Maria Somolinos,1 Diego García,1 Rafael Pagán,1 and Bernard Mackey2*

Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Miguel Servet 177, 50013 Zaragoza, Spain,1 Department of Food Biosciences, University of Reading, P.O. Box 226, Whiteknights, Reading RG6 6AP, United Kingdom2

Received 24 April 2008/ Accepted 18 October 2008

The aim was to investigate (i) the occurrence of sublethal injury in Listeria monocytogenes, Escherichia coli, and Saccharomyces cerevisiae after high hydrostatic pressure (HHP) treatment as a function of the treatment medium pH and composition and (ii) the relationship between the occurrence of sublethal injury and the inactivating effect of a combination of HHP and two antimicrobial compounds, tert-butyl hydroquinone (TBHQ) and citral. The three microorganisms showed a high proportion of sublethally injured cells (up to 99.99% of the surviving population) after HHP. In E. coli and L. monocytogenes, the extent of inactivation and sublethal injury depended on the pH and the composition of the treatment medium, whereas in S. cerevisiae, inactivation and sublethal injury were independent of medium pH or composition under the conditions tested. TBHQ alone was not lethal to E. coli or L. monocytogenes but acted synergistically with HHP and 24-h refrigeration, resulting in a viability decrease of >5 log10 cycles of both organisms. The antimicrobial effect of citral depended on the microorganism and the treatment medium pH. Acting alone for 24 h under refrigeration, 1,000 ppm of citral caused a reduction of 5 log10 cycles of E. coli at pH 7.0 and almost 3 log10 cycles of L. monocytogenes at pH 4.0. The combination of citral and HHP also showed a synergistic effect. Our results have confirmed that the detection of sublethal injury after HHP may contribute to the identification of those treatment conditions under which HHP may act synergistically with other preserving processes.

* Corresponding author. Mailing address: Department of Food Biosciences, University of Reading, P.O. Box 226, Whiteknights, Reading RG6 6AP, United Kingdom. Phone: 44 118 378 8727. Fax: 44 1189 310 080. E-mail: b.m.mackey{at}reading.ac.uk

{triangledown} Published ahead of print on 24 October 2008.

Applied and Environmental Microbiology, December 2008, p. 7570-7577, Vol. 74, No. 24
0099-2240/08/$08.00+0     doi:10.1128/AEM.00936-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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