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Applied and Environmental Microbiology, March 2007, p. 1601-1611, Vol. 73, No. 5
0099-2240/07/$08.00+0     doi:10.1128/AEM.02198-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Individual and Combined Effects of pH and Lactic Acid Concentration on Listeria innocua Inactivation: Development of a Predictive Model and Assessment of Experimental Variability{triangledown}

M. Janssen,1 A. H. Geeraerd,2 A. Cappuyns,1 L. Garcia-Gonzalez,1 G. Schockaert,1 N. Van Houteghem,3 K. M. Vereecken,1,{dagger} J. Debevere,3 F. Devlieghere,3 and J. F. Van Impe1*

Division of Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, Katholieke Universiteit Leuven, W. de Croylaan 46, B-3001 Leuven, Belgium,1 Division of Mechatronics, Biostatistics and Sensors (MeBioS), Department of Biosystems (BIOSYST), Katholieke Universiteit Leuven, W. de Croylaan 42, B-3001 Leuven, Belgium,2 Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium3

Received 19 September 2006/ Accepted 22 December 2006

In food technology, organic acids (e.g., lactic acid, acetic acid, and citric acid) are popular preservatives. The purpose of this study was to separate the individual effects of the influencing factors pH and undissociated lactic acid on Listeria innocua inactivation. Therefore, the inactivation process was investigated under controlled, initial conditions of pH (pH0) and undissociated lactic acid ([LaH]0). The resulting inactivation curves consisted of a (sometimes negligible) shoulder period followed by a descent phase. In a few cases, a tailing phase was observed. Depending on the conditions, the descent phase contained one or two log-linear parts or had a convex or concave shape. In addition, the inactivation process was characterized by a certain variability, dependent on the severity of the conditions. Furthermore, in the neighborhood of the growth/no growth interface sometimes contradictory observations occurred. Overall, the individual effects of the influencing factors pH and undissociated lactic acid could clearly be distinguished and were also apparent based on fluorescence microscopy. Appropriate model types were developed and enabled prediction of which conditions of pH0 and [LaH]0 are necessary to obtain a predetermined inactivation (number of decimal reductions) within a predetermined time range.

* Corresponding author. Mailing address: Department of Chemical Engineering, W. de Croylaan 46, B-3001 Leuven, Belgium. Phone: 32 16 321466. Fax: 32 16 322991. E-mail: jan.vanimpe{at}cit.kuleuven.be.

{triangledown} Published ahead of print on 5 January 2007.

{dagger} Present address: Federal Agency for the Safety of the Food Chain, WTC III, Simon Bolivarlaan 30, B-1000 Brussels, Belgium.

Applied and Environmental Microbiology, March 2007, p. 1601-1611, Vol. 73, No. 5
0099-2240/07/$08.00+0     doi:10.1128/AEM.02198-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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