Modelling the secondary shelf life of packaged breadsticks

The aim of this study was to establish a correlation between the secondary shelf life (SSL) of packaged breadsticks and their residual shelf life (RSL). To this aim, the packaged product was stored at 38 °C and external water activity of 0.912. Throughout the entire storage period, the internal water activity was monitored. At regular time intervals (every 7 days), the primary package was opened, and the internal water activity continued to be monitored. The above set of data were used to estimate both the primary shelf life (PSL) and the SSL. To this aim, two different models were proposed to describe the experimental data. The first assumes, among the other hypotheses, that the water sorption isotherm can be described by the GAB model, whereas the second assumes a linear relationship between the water absorbed by the breadsticks and the water activity. Both mathematical approaches were found satisfactory. Accordingly, the PSL and SSL values obtained from the two models were very similar. Considering the complexity of the models and their performance in describing the data, the approach based on a linear water sorption isotherm appears the most appropriate, as it offers a good balance between accuracy and simplicity. As expected, SSL is consistently lower than RSL and decreases as RSL decreases.