| The adsorption and desorption isotherms of equilibrium moisture contents of six soybean meals samples were determined by gravimetric metho d. The modified Chung-Pfost equation (MCPE), modified Halsey equation (MHAE), modified Henderson equation (MHE), modified Guggenheim-Anderson-de Boer (MGAB), modified Oswin equation (MOE) and Strohman-Yoerger equation (STYE) were employed to fit the sorption datas, and the better fitting equations were determined to be MGAB, MHAE and MOE. The sorption isosteric heat of soybean meal decreased rapidly with moisture increasing, and the desorption isosteric heat was significantly higher than adsorption isosteric heat at the same temperature when the moisture was below 15%. However, when the moisture was above 15%, the sorption isosteric heat of soybean meal changed gently with moisture increasing, and the desorption isosteric heat was similar to the adsorption isosteric heat at the same temperature. When the moisture was below 15%, both the adsorption isosteric heat and desorption isosteric heat of soybean meal at low temperature were higher than those at high temperature. When the moisture was 17.5%, the sorption isosteric heat of soybean meal was close to the latent heat of pure water, about 2 500 kJ/kg. The isotherm analysis results showed that the absolutely safe moisture and relatively safe moisture of soybean meal were 12.48% and 13.90%,respectively. |
