Mejlholm, O. and Dalgaard, P. (2007b). Modeling and predicting the growth of lactic acid bacteria in lightly preserved seafood and their inhibiting effect on Listeria monocytogenes  J. Food Prot. 70, 2485-2497.

Mejlholm, O, Dalgaard, P. (2013). Development and validation of an extensive growth and growth boundary model for psychrotolerant Lactobacillus spp. in seafood and meat products. Int. J. Food Microbiol. 167, 244-260.

This model includes the effect of 12 environmental parameters (See Table above) on the growth of psychrotolerant Lactobacillus  spp. in fresh and processed seafood and meat products. FSSP predicts growth of these psychrotolerant lactic acid bacteria (LAB) without using a lag phase as numerous studies have confirmed their grow without a significant lag time in fresh and lightly preserved seafood and meat products. See the FSSP dialog box and output window below (Fig. 1).

Fig. 1. The graph above shows how a combination of benzoic and sorbic acid can prevent growth of LAB at 5°C in a product with pH 5.5 (blue curve). FSSP specifically indicates  the time needed for the concentrations of LAB to increase 100-fold and to reach 7.0 log (cfu/g) under the selected product characteristics and storage conditions. The concentrations of LAB shown in the bar at the bottom of the output window was obtained by using the mouse to click on the graph at a specific point in time.

Fig. 2. Effect of two simple temperature profiles on predicted growth of psychrotolerant Lactobacillus spp.

Secondary growth model:

Eqn. 2 below shows the extensive secondary growth model for psychrotolerant Lactobacillus spp. This simplified cardinal parameter type model describe how the maximum specific growth rate  (µ_max, h^-1) at a reference temperature of 25°C is reduced when environmental parameters become less favourable for growth. The terms for each of the environmental parameters all has a value between 0 and 1. FSSP predicts the growth boundary of psychrotolerant Lactobacillus spp. as the combination of environmental conditions resulting in µ_max = 0 and a specific term (ξ) is included in the cardinal parameter models to take into account the effect of interaction between all the different environmental parameters (Eqn. 2).

Evaluation and validation of the psychrotolerant Lactobacillus spp. growth model: 

The model included in FSSP for prediction of psychrotolerant LAB growth has been evaluated by comparison of observed and predicted growth in inoculated challenge tests and in naturally contaminated products as shown in the Table below. The model performed very well and the bias factors was within the ranges for successful model validation of 0.85 < Bias factor < 1.25 (Mejlholm and Dalgaard, 2013).