Moisture Sorption Isotherms of Oolong Tea

The sorption isotherms of Oolong tea were determined at temperatures ranging from 5 to 50 °C. Estimated parameters and fitting ability for nine equilibrium relative humidity (ERH) models were evaluated. The modified Oswin equations were found to be an adequate model of three parameters to describe the sorption data. The Andrieu model was the only adequate model of four parameters. In comparing the results of this study with previously published data, it was found that the sorption properties were affected by species and manufacture techniques. The Guggenheim–Anderson–de Boer (GAB) model was not an adequate model as indicated by checking residual plots. The monolayer moisture content calculated from the Brunauer–Emmett–Teller (BET) model was lesser than that calculated from the GAB model. The errors of moisture content determined by measuring the ERH and temperature of samples was within 0.35%.