Shelf life of modified atmosphere packed cooked meat products: addition ofNa-lactate as a fourth shelf life determinative factor in a model and product validation

Cooked meat products are often post-contaminated because of a packaging and /or slicing step after the pasteurisation process. The shelf life is theref ore limited and can be extended by adding Na-lactate. A previously develope d model for the spoilage of gas packed cooked meat products, including temp erature, water activity and dissolved CO2 as independent variables, was ext ended with a fourth factor: the Na-lactate concentration in the aqueous pha se of the meat product. Models were developed for the maximum specific grow th rate mu(max) and the lag phase lambda of the specific spoilage organism Lactobacillus sake subsp. carnosum. Quadratic response surface equations we re compared with extended Ratkowsky models. In general, response surface eq uations fitted the experimental data best but in the case of mu(max), the r esponse surface model predicted illogical growth behaviour at low water act ivities and high Na-lactate concentrations. A extensive product validation of the mathematical models was performed by means of inoculated as well as naturally contaminated industrially prepared cooked meat products. The devi ations of the experimentally determined versus predicted growth parameters in inoculated cooked meat products were in general small. Both types of mod els were also able to predict the shelf life of naturally contaminated cook ed meat products, except for pate where an under-estimation of the shelf li fe was predicted by the response surface equations. The validation studies revealed higher accuracy of the extended Ratkowsky models in comparison to the response surface equations. A significant shelf life extending effect o f Na-lactate was predicted, which was more pronounced at low refrigerated t emperatures. A synergistic effect has also been noticed between Na-lactate and carbon dioxide which, at least partly, could be explained by the pH-dec reasing effect of CO2. (C) 2000 Elsevier Science B.V. All rights reserved.