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Modeling of sorption isotherms of spring barley kernels :Microwave density-independent permittivity function correlated towater activity

Zeesham Ahmad, Ashutosh Prasad, H.N.Singh

The present study aims at correlating water activity (aw) to density independent microwave permittivity function () for spring barley (Hordeum Vulgares L.) kernels in the sorption isothermcorresponding to 240C. The data for  were derived fromthe experimental results of relative permittivity and loss factor measured at 2.45 GHz and nine moisture levels from8.2%to 25.1%,(wet basis) all taken fromthe literature. These values of relative permittivity for bulk materials were then converted to those for solids with the help of eight equations for effective permittivity of random media, such as the logarithmic law of mixing. With these data, quadratic model for variation of two dielectric properties, relative permittivity and loss factor, as functions of decimal moisture contents, have been proposed. Four[EquilibriumRelativeHumidity (ERH)/Equilibriummoisture content (EMC)] sorption isotherms were converted to aw/ type of sorption isotherms. The comparative goodness-of-fit for the four different isotherms was quantified through sigmoidal curve -fitting technique. The evaluated parameters showed that Modified Henderson Equation (MHE) provided the best fit with experimental results having minimal [chi-square/degrees of freedom(DOF)]7.6510-12 and maximumcoefficient of determination (r2) 0.9999. Consequently, it was supposed to be the most appropriate model in predicting sorption processes of spring barley kernels for the chosen range of temperature and water activity.