Abstract

Moisture sorption isotherms of Pleurotus ostreatus were determined at three different temperatures (10, 30 and 40) and relative humidity (6 to 88%), using standard static gravimetric method. The samples were used to determine the equilibrium moisture content and the data fitted to the Guggenheim-Anderson-de Boer (GAB) equation to describe the moisture adsorption characteristics within the water activity used for this study. Model parameters c, k and Mo were derived. The GAB monolayer moisture values (Mo) were 0.179, 0.163 and 0.123 at 10, 30 and 40°C respectively. The c and k value decreased from 0.729 to 0.613 at 10°C and 19.455 to 18.551 at 30°C, and increased to 0.712 and 24.737 when the temperature was further increased to 40°C. The mean relative percent modulus (%E) were 1.318, 5.393 and 3.224% at 10, 30 and 40°C respectively. The r2 values obtained varied between 0.980 and 0.997, indicating strong correlations between the experimental and predicted data; whereas the error values ranged from 0.007 to 0.017, showing very good fitness between the experimental moisture sorption and the modeled sorption. Thus, GAB model could be used to predict the moisture sorption behavior of P. ostreatus mushroom at the range of water activity used in this study.

Key words: Pleurotus ostreatus, mushroom, Guggenheim-Anderson-de Boer (GAB) model, adsorption, isotherm, monolayer.

Abbreviation

a_w, water activity; M_exp, the experimental moisture content; M_cal, the calculated moisture content; M_e, equilibrium moisture content of sample (g/g db); M_o, monolayer moisture value in g H₂0/100 g dry matter; α, k/M_o (1/c - 1); β, 1/M_o (1 - 2/c); γ, 1/M_o k c; c and k, sorption constants; c, constant related to thermal effects; k, the constant related to the properties of multilayer water molecules with respect to the bulk liquid; r², coefficient of determination; %E, mean relative percent deviation modulus; SEE, standard error of estimate.