芝麻平衡水分及吸着等热研究

Study on sorption equilibrium moisture and isosteric heat of sesame

采用静态称重法测定了我国4个芝麻品种的平衡水分等温线，并采用CAE、修正Chung—Pfost（MCPE）、修正Halsey（MHAE）、修正Henderson（MHE）、修正Guggenheim—Anderson—deBoer（MGAB）、修正Oswin（MOE）及Strohman—Yoerger（STYE）7个水分吸着方程进行拟合，指出MOE最适合描述芝麻平衡含水率（EMC）-平衡相对湿度（ERH）之间的关系，并用于计算芝麻吸着等热。在含水率〈7．5％湿基，芝麻吸着等热均随含水率增大而快速减少，同一温度下的解吸等热显著高于吸附等热。在含水率7．5％以上，芝麻吸着等热随含水率增大而变化平缓，同一温度下的解吸等热趋同于吸附等热。在含水率〈7．5％湿基条件下，较低温度下的芝麻吸附等热与解吸等热均高于较高温度。在含水率10％湿基的自由水点，芝麻的吸着等热（汽化热）接近纯水的潜热，约是2450kJ／kg。在测定温度10～35℃范围，黑芝麻吸着等热数值类似白芝麻吸着等热数值。计算的25℃芝麻储运绝对安全水分是6．46％，相对安全水分是6．94％。

Equilibrium moisture content（EMC） data for sesame seeds of four Chinese varieties were collected by gravimetric method at 11% to 96% relative humidity（ERH） and 10,15,20,25,30,and 35℃ above nine saturated salt solutions.Seven models, named CAE, Modified - Chung - Pfost （ MCPE）, Modified - Halsey （ MHAE）, Modified - Henderson （MHE）, Modified- Guggenheim- Anderson- deBoer （ MGAB ）, Modified- Oswin （MOE） and Strohman- Yoerger（STYE） were fitted to the sorption data, and the best fitted equation was determined to be MOE.The isosteric heats for both sesame adsorption and desorption decreased rapidly with increasing seed moisture initially,however,after the moisture was more than 7.5% wet basis （wb）, they decreased tardily with increasing moisture content（ mc）.The isosteric heats of sesame desorption were considerably higher than those of adsorption below 7.5% mc.The heat of vaporization of sesame approached the latent heat of pure water at a moisture content of about 10% wb,which was about 2450kJ/kg.The isosteric heats of black sesame sorption were similar to those of white sesame sorption.The absolutely safe storage moisture content of sesame at 25℃ was 6.46% wb, and the relatively safe mc at 25℃ was 6.94%wb.