Estimation of water activity from pH and °Brix values of some food products

In this study, a predictive model for the estimation of water activity ( a w 25 ° C ) as a function of pH (1.00–8.00) and °Brix (0–82.00) values of simulated food solutions (SFS) was developed, through response surface methodology. Response fit analyses resulted in a highly significant (pH < 0.0001) square root polynomial model that can predict a w 25 ° C of SFS in terms of pH and °Brix values within the defined variable ranges. The linear, quadratic and interactive influences of pH and °Brix on a w 25 ° C were all significant (pH < 0.0001). Model validations in SFS and in a number of actual food systems showed that the model had acceptable predictive performance, as indicated by the calculated accuracy and bias indices.