Moisture sorption and the applicability of the Brunauer-Emmet-Teller (BET)equation for blanched and unblanched mushrooms

Moisture sorption isotherms of blanched and unblanched mushrooms over 0.11- 0.75 a(w) were determined at 27 degrees C and 37 degrees C by using the sta tic gravimetric method. Adsorption and desorption behaviors of blanched and unblanched mushrooms were compared. The unblanched material adsorbed more water than that of the blanched. In desorption isotherms, the equilibrium m oisture contents of the unblanched material were found to be higher than th ose of the blanched throughout the entire a, range. The BET equation was te sted to fit the experimental moisture sorption data over the 0.11-0.43 a(w) , 0.11-0.55 a(w), 0.11-0.64 a(w) and 0.11-0.75 a(w). Nonlinear regression a nalysis was used for the determination of the parameters in the equation. T he quality of the fit of the BET model over each a, range was judged from t he value of the relative percent root mean square (% RMS). The moisture sor ption behavior over 0.11-0.43 a(w) of mushrooms has indicated that the BET equation is applicable generally up to 0.43 a(w). Monolayer moisture conten ts and C constants in the BET equation obtained for each a(w) interval were reported. The water activities corresponding to the monolayer values have been determined and discussed related to mushroom storage. The net isosteric hears of adsorption and desorption were estimated from eq uilibrium sorption data, using the integrated form of the Clausius-Clapeyro n equation. The heats of adsorption/desorption decreased with increase in m oisture content and approached to a constant value. It was, concluded that moisture adsorption/desorption occurred by physical mechanisms at high mois ture contents,but at low moisture contents, besides physical adsorption, ch emisorption was also observed.