Moisture adsorption behaviour of biscuit during storage investigated by using a new Dynamic Dewpoint method

• Equilibrium moisture content of biscuits underwent modifications during storage.
• The monolayer moisture content increased during product ageing.
• Hardness decreased and peroxide values increased as a consequence of product hydration.
• DDI is a valid tool to investigate water interactions on biscuit during storage.

The changes in moisture adsorption isotherms of commercial biscuits during storage were investigated by means of a rapid Dynamic Dewpoint Isotherms (DDIs) method. Moreover, the relationships between the changes in moisture content and some quality characteristics of biscuits (moisture, aw, peroxide value – PV and texture) were studied during 92 days of storage at 35 °C. GAB model was used to fit the experimental sorption behaviours. During storage, moisture content and aw of biscuits increased and the obtained isotherms showed modifications in behaviour and shape. Significant changes were observed in PV values and texture, particularly during the first 40 days of storage.The monolayer moisture content, obtained by the BET equation, significantly increased during storage from 1.473 to 2.080 g water 100 g db−1, probably because of the increase in the active sites for water binding due to the chemical and physical changes of the main components, induced by product ageing.