Abstract: In order to reveal the relationships between temperature and moisture content and water activity (aw) of peanut shell (PS) and peanut kernel (PK) and thus to improve the storage stability of peanut, the moisture adsorption isotherms of PS and PK were investigated at 10, 20 and 30 ℃ by the static weighing method. Thermodynamic properties such as net isosteric heat of sorption (qst), differential entropy (Sd), spreading pressure, integral entropy, integral enthalpy, enthalpyentropy compensation, and glass transition temperature (Tg) of PS and PK were also discussed. The results showed that the water adsorption of PK and PS followed a typical type Ⅲ isotherm behavior, and the water contents of PK and PS increased with increasing aw. The GAB model showed the best fit with the experimental data. The qst and Sd of PS and PK decreased with increasing moisture content. The spreading pressure increased with increasing aw, and decreased with increasing temperature. The integral enthalpy decreased with increasing moisture content, whereas reverse trend was observed for the integral entropy. Both qst and Sd of PS were higher than those of PK, while the spreading pressure of PK at the same temperature was higher than that of PS. At the same moisture content, the integral enthalpy of PK was lower than that of PS, whereas integral entropy of PK was higher than that of PS. The water adsorption processes of PS and PK were both a spontaneous process driven by enthalpy and Tg of PS and PK decreased with increasing water content, with the former being higher than the latter at the same water content. According to the state diagram, at 10 ℃, critical water activity and critical water content were 0.80 and 0.175 4 g/g for PS and 0.68 and 0.095 5 g/g for PK, respectively. These results can provide a theoretical basis for peanut drying and improved storage stability of dehydrated peanut.

Key words: peanut, moisture adsorption isotherms, thermodynamic properties, glass transition temperature, state diagram