Moisture Sorption Isotherms And Safty Moisture In Summer Storage Conditions Of Soybean

This paper mainly studied on the moisture sorption isotherms(adsorption anddesorption) of domestic soybean(beidou No.3) and imported soybean fromArgentine,then studied safty moisture in simulative summer storage conditions. Themain results are as follow.Moisture adsorption and desorption isotherm of domestic and imported soybeanat temperatures(10,20,30,40℃) and relative humidity from11.29%to95.96%weredetermined using static gravimetric method. Drawn sorption isotherms to reflectrelationships of equilibrium moisture content and water activity(Aw).The experi-mental data were fit by five models(modified Henderson(MHDE),modified Chung-Pfost(MCE), modified Halsey(MHYE),modified Oswin(MOE),modified Guggenhein-Anderson–deBoer(MGAB)). The results showed that:(1) The sorption isotherms were nearly coincident at a specific temperatureconditions. Characteristics of adsorption and desorption were basically the same.(2) The equilibrium moisture content(EMC) increased with the increasing ofwater activity.The EMC increased fast at low Aw，and increased slow at midiumAw,then increased fast at high Aw. The sorption isotherms followed the characteristictype Ⅱsigmoid shape classification.(3) The sorption isotherms were affected by temperature.In sorption isothermsfiguers,the adsorption and desorption isotherms were ordered from top to downaccording the temperature from low to high.(4) The adsorption isotherms were located in the bottom of desorption isothermsat10,20,30and40℃,the hysteresis appears more obvious as the temperaturedecrease.(5) Statistics test show that: experimental data fitted with five models to sorptionisotherm of domestic soybean were valid.Overall, MGAB was identified as the mostappropriate model for adsorption isotherms,MOE was identified as the mostappropriate model for desorption isotherms.Domestic soybean were set4initial moisture content conditions(12.1%,13.3%,14.2%,15.4%), imported soybean were also set4initial moisture contentconditions (10.3%,11.2%,12.1%,13.3%).They were stored at three temperatures(25,30,35℃) Simulated in summer storage conditions and sampled once every15 days.Moisture content, germination rate, nitrogen solubility index （NSI）,fatty acidvalue and mold content were measured during the storage,the odor of soybean wasalso analyzed by electronec nose, the experiments were lasted105days. The resultsshowed that:(1) The moisture content was slowly descend in the storage time, the higher thestorage temperature was, the more rapidly the reducing of moisture content.(2) The germination rate and NSI were decreased with the prolonging of storagetime.The higher the storage temperature was, the more rapid reduction of germinationrate and NSI with the same initial moisture content were. The higher initial moisturecontent was, the more rapid reduction of germination rate and NSI at the sametemperature were.The effect of initial moisture content and storage time ongermination rate and NSI were extremely significant（P<0.01）.(3) The fatty acid value and mold content were increased with the prolonging ofstorage time. The higher temperature was, the more rapid increase of fatty acid valueand mold content were. The higher initial moisture content was, the more rapidincrease of fatty acid value and mold content were at the same temperature. The effectof initial moisture content and storage time on fat acid value were extremelysignificant（P<0.01）. The effect of initial moisture content on mold content wasextremely significant, the effect of storage time on mold content was extremelysignificant at25℃and significant at25and30℃to domestic soybean（0.01<P<0.05）.But the effect of storage time on mold content was not significant toimported soybean（P>0.05）.(4) Electronic nose was able to identify the samples stored at different initialmoisture content by PCA and LDA methods.When the initial moisture content of domestic soybean were12.1%and13.3%,initial moisture content of imported soybean were10.3%and11.2%, the germinationrate and NSI decreased slowly, the fatty acid value and mold content increased slowly.Based on moisture sorption isotherms and the change of quality in storage of atdifferent initial moisture content of two soybeans, concluded that the safty moisturedomestic soybean is from12%to13%,and the safty moisture imported soybean isfrom10%to11%in summer storage conditions.