Mathematical Modeling of Lactobacillus Viridescens Growth in Vacuum Packed Sliced Ham under non Isothermal Conditions

Abstract

Lactic acid bacteria (LAB) are responsible for the spoilage of vacuum packed meat products, as ham. Temperature is the main factor affecting the microbial dynamics and its variation during the production, distribution and storage of foods is considerable. Thus, the use of mathematical models to describe the microbial behavior under variable temperatures can be very useful in predicting the food shelf life. This study evaluated the growth of Lactobacillus viridescens in sliced ham under non isothermal conditions, and assessed the predictive ability of the Baranyi and Roberts model using parameters obtained isothermally in culture medium (MRS). To obtain the BAL growth, the fresh ham piece was sterilized, sliced, inoculated with bacteria and stored in a temperature-controlled incubator. For the establishment of the secondary models, the primary model parameters were obtained isothermally in the culture medium at 4, 8, 12, 16, 20 and 30° C, in which there was no lag phase observed; the square root model was selected to describe the dependence of the μmax parameter (maximum specific growth rate) with the temperature, and the ymax parameter (maximum population) was represented by an average because there was no significant influence of the temperature. The mathematical models were validated with L. viridescens growth data in ham under five variable temperature conditions (NI-1 (4-8-12-16°C), NI-2 (12-16-20-25°C), NI-3 (25-20-16-12-8-4°C), NI-4 (16-12-8-4°C) and NI-5 (12-8-4-8-12°C)), and its predictive ability were assessed through statistical indexes (bias factor, accuracy factor and RMSE), with good results (bias factor between 0.9450 and 1.0326; accuracy factor between 1.0382 and 1.0682, and RMSE between 0.7641 and 1.3317), especially in increasing temperature, where the prediction was safe. The validated model can be used to estimate the shelf life of a commercial ham under different temperature conditions.