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Module  Water activity calculation for seafood
Reference Ross, T. and Dalgaard, P. (2004). Secondary models. In: McKeller, R.C.and Lu, X. (Eds.), Modeling Microbial Responses in Foods. CRC Press, Boca Raton, USA, pp. 63-150.


To predict the effect of NaCl on growth of microorganisms in seafood the concentration of water phase salt (WPS) or water activity (aw) is ofter needed (Eqn. 1-3).  

                                              Eqn. 1

For mixtures of NaCl and water there is direct relation between the WPS content and aw (Eqn. 2, Resnik and Chirife 1988). For cured seafood where NaCl is the only major additive the same relation has been observed e.g. for cold-smoked salmon (Jørgensen et al. 2000).     

                              Eqn. 2

                                        Eqn. 3


To facilitate conversion between water activity and WPS and to calculate WPS from seafoods content of NaCl and dry matter a 'Water activity calculation for seafood' module has been included in FSSP. See dialog box below.  The FSSP module is not always directly related to the microbial growth models and after calculation of water activity or WPS values these need to be use in the relevant FSSP modela. To facilitate transfer of relevant WPS values a dedicated calculator has been added to several models as shown below to the right.