Determination of Temperature Dependent Growth Parameters in Psychrotrophic Pathogen Bacteria and Tentative Use of Mean Kinetic Temperature for the Microbiological Control of Food

Abstract

Temperature is the main factor to control the microbial growth in perishable foods. The psychrotrophic pathogen bacteria are microorganisms of concern for food products with extended shelf life in chilling conditions. The aims of this work were two. Firstly, to evaluate growth behavior of Aeromonas hydrophila DSM-30187, Listeria monocytogenes DSM-20600, and Yersinia enterocolitica DSM-27689 strains, at different temperatures (4, 7, 10, 15, 25, and 30°C) and starting cell concentrations (10 and 10⁶ CFU/mL), in order to determine the activation energies (E _a) of the relevant lag phases and growth rates. Secondly, to investigate if Mean Kinetic Temperature (MKT) might be applied in recording temperature devices to alert a thermal abuse in a management control system for food safety. As expected, lag phase and growth rate proved to be heavily affected by temperature whereas the inoculum size did not. The E _a values involved in the duration of latent periods, calculated on the basis of the Arrhenius model, were comparable for A. hydrophila and L. monocytogenes strains (from 21.3 to 24.4 kcal/mol), while significantly differed for Y. enterocolitica (16.6 kcal/mol). The E _a values of growth rates were similar for A. hydrophila and L. monocytogenes strains (from 20.9 to 21.1 kcal/mol), while were considerably lower for Y. enterocolitica (from 14.2 to 16.7 kcal/mol). The use of MKT is widespread and well-accepted in pharmaceutical field as convenient method for estimating drugs degradation in relation to storage temperature. The E _a value of the lag phase found for L. monocytogenes (23.9 ± 1.2 kcal/mol) was included in the MKT formula. In this work, the air temperature of two chilling rooms was monitored during the normal operating activity in a catering company for a period of 8 months. The MKT profiles were then compared with those of mean temperatures in different conditions (short or prolonged events of thermal abuse) with the purpose to evaluate if it may be applicable to reduce false alarms without lowering the safety level of stored food.

Keywords: Aeromonas hydrophila; Ea values; Listeria monocytogenes; Yersinia enterocolitica; food safety; growth parameters; mean kinetic temperature.

Figure 1

Mean values and relative error bars of lag phases (A) and growth rates (B) observed at different temperatures and inoculum sizes for Aeromonas hydrophila DSM-30187 strain.

Figure 2

Mean values and relative error bars of lag phases (A) and growth rates (B) observed at different temperatures and inoculum sizes for Listeria monocytogenes DSM-20600 strain.

Figure 3

Mean values and relative error bars of lag phase times (A) and growth rates (B) observed at different temperatures and inoculum sizes for Yersinia enterocolitica DSM-27689 strain.

Figure 4

Arrhenius model plots based on lag phase times (A) and growth rates (B) for A. hydrophila DSM-30187, lag phase times (C) and growth rates (D) for L. monocytogenes DSM-20600, lag phase times (E) and growth rates (F) for Y. enterocolitica DSM-27689. Data observed at high level of inoculum (10⁶ CFU/ml) are drawn as ▴ and dotted lines; data at low level of inoculum (10 CFU/ml) are drawn as • and full lines.

Figure 5

Recorded temperature profiles (—) and relative MKT values ( - - - ) for a 8 days sampling period, showing two different situation of early (A) and late (B) peak thermal abuses, and for a 12 h sampling period, showing a prolonged thermal abuse (C) and a series of short thermal abuses (D).