Thermodynamic sorption properties of potato and sweet potato flakes

The moisture sorption isotherms of potato and sweet potato flakes were determined using a gravimetric method at 15, 20, 25 and 30 °C for water activity ranging from 0.1 to 0.9. The GAB was found to be the most suitable for describing the relationship between equilibrium moisture content and water activity for the whole range of temperatures and relative humidities. The differential and integral thermodynamic functions of enthalpy and entropy were estimated from the sorption data for potato and sweet potato flakes. The differential enthalpy was determined using the Clausius–Clapeyron equation and decreased with increase in moisture content, the same behavior as found for differential entropy. From the values obtained for differential enthalpy and entropy, it was verified that the compensation theory could be applied, the process being carried out by enthalpy (Tβ > Thm) and non-spontaneous (ΔG > 0). The spreading pressures increased with increasing water activity for all the temperatures studied. With respect to the integral properties, it was observed that the enthalpy increased with moisture content, but the entropy decreased. It was also shown that for the moisture range evaluated, the values for integral entropy were negative.

► The thermodynamic functions for potato and sweet potato flakes were studied.
► The differential enthalpy and differential entropy decreased with increase in moisture content.
► The values indicated that the process was not spontaneous (ΔG > 0).
► The net integral enthalpy increased with moisture content.
► The net integral entropy presenting negative values.