Moisture Sorption Behavior of Potato Crisps and Biscuits

Sorption isotherms were measured for potato crisps and digestive biscuits at 20°C and 30°C using a novel method, and water activity models were applied. The sorption properties of finished food products are rarely measured due to stability issues associated with oil content. The novel method presented in this study allows for the accurate quantification of the sorption properties and finished moisture contents of complex foods. The quantification of the sorption properties of potato crisps demonstrated that the sorption properties are not significantly affected by the frying process. The final packaged moisture content of potato crisps was measured to be 0.017 kg kg^-1 wet basis, with a calculated total heat of sorption of 5.2 × 10⁶ J kg^-1. The final packaged moisture content of biscuits was measured to be 0.025 kg kg^-1 wet basis, with a calculated total heat of sorption of 6.7 × 10⁶ J kg^-1. The presented moisture dependent heat of sorption is particularly useful when considering the design of drying equipment. The study affirms previous observations that the BET theoretical sorption model accurately describes the sorption monolayer content. It does not accurately describe the behavior of multilayer and condensation at higher moisture contents, a recognized limitation of the model. The Peleg equation, which is purely a mathematical curve-fitting model rather than a theoretical model, provided the best overall average fit, with an average mean relative error (MRE) of just 0.41%. PRACTICAL APPLICATIONS: This study presents a novel method for accurately measuring the sorption isotherms of finished products without the need for hazardous chemicals. New sorption data for potato crisps and biscuits are presented that are of interest for industrial finish drying applications.