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Modeling of the adsorption isotherm of Pleurotus ostreatus using Guggenheim-Anderson-de Boer (GAB) equation

 Modeling of the adsorption isotherm of Pleurotus ostreatus using Guggenheim-Anderson-de Boer (GAB) equation    

 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. In this work, freshly cultivated P. ostreatus mushroom were sorted according to uniform maturity, size and cleaning. The average initial moisture content (dry basis) of the mushroom samples was determined using the standard method (AOAC, 2002). The adsorption isotherms of the mushroom samples were determined using a standard static gravimetric method at air temperature of 10, 30, and 40°C with five saturated salt solutions of known water activity. The prepared fresh samples were put into a container saturated with saturated salt solutions. About 3 g bone dried sample was placed in a Petri dish inside five dessicators containing saturated salt solutions of KOH, MgCl2, (MgNO3)2, NaCl2, Na2C7H5O2 with relative humidity 6, 33, 52, 75 and 88% respectively. At high relative humidity (aw > 0.7), toluene (1.5 ml) was placed in the desiccators to prevent microbial growth. The dessicators were placed inside incubators maintained at three different temperatures of 10, 30, and 40°C. The sample weight was measured periodically until constant value was reached, where the samples were assumed to be at equilibrium and subsequently the moisture content of the sample was determined by means of hot-air oven (AOAC, 1990). The equilibrium moisture content (EMC) of the mushroom sample was subsequently plotted against the water activity to obtain sorption isotherm curves. The data for the water adsorption were fitted to the GAB equation (Van de Berg and Bruin, 1981) to describe the moisture adsorption process.