Influence of surface water activity on freezing/thawing times and weight loss prediction

A common assumption in heat and mass transfer modelling of processes such as chilling and freezing is to consider water activity (aw) being constant or equal to 1. However, this constant value assumption does not represent the actual variation of water activity during the process. In the present work, the effect of different values of water activity on the freezing/thawing times and weight loss prediction of cured cooked pork and beef, and chicken meat was studied. Experimental sorption data of these meats were previously obtained, and the results were incorporated to the developed computer simulation program. An explicit finite difference scheme, which incorporates the mass transfer and variation of aw was used in the analysis. Experimental data on freezing/thawing times and weight loss were also obtained to verify and compare with the model predictions.The high water activity range (aw = 0.85, 0.9, 0.95 and 1) was analysed. In general and for all the meats considered, the lowest error was obtained when variable aw was used. Results indicated that if data on the sorption isotherm are not available a constant water activity value of 0.875 could be used instead to predict the freezing time and weight loss for cooked cured pork and beef, and a value of 0.9 for chicken meat; while for the modelling of the thawing process aw values of 0.95 and 1 are recommended for cured cooked pork and beef and chicken meat, respectively. Hence, water activity is an important factor and should be incorporated in the modelling in order to improve the accuracy of the predictions.