香椿干燥特性及其特征香气化合物热降解动力学

Drying Characteristics of Toona sinensis and Thermal Degradation Kinetics of Its Characteristic Aroma Compounds

对香椿干燥过程中水分迁移规律进行研究,同时考察不同热处理条件对香椿的特征香气有机化合物之一2-巯基-3,4-二甲基-2,3-二氢噻吩(2-Mercapto-3,4-Dimethyl-2,3-Dihydrothiophene,MDD)稳定性的影响,分析MDD热降解的动力学以及热力学规律。结果表明:热处理温度越高,香椿干燥速率越快,符合传统的干燥速率变化规律。MDD降解过程符合一级动力学反应规律和Arrhenius模型,反应速率常数介于0.0155~0.0345 min^(-1)之间,并且随着处理温度的升高而增大,不同温度下半衰期分别为44.719、32.239、20.091 min,随着干燥处理温度的升高而呈现出减少的变化趋势,反应的活化能(Ea)为39.052 kJ/mol。焓变(ΔH)为正值说明MDD热降解过程是吸热反应,吉布斯自由能(ΔG)也为正值,说明MDD热降解反应为非自发反应。研究可为有效控制香椿加工生产过程特征风味物质的降解提供理论依据。

The moisture transfer pattern during the drying process of Toona sinensis was studied,and the effects of different heat treatment conditions on the stability of the characteristic aroma compound of Toona sinensis,2-mercapto-3,4-dimethyl-2,3-dihydrothiophene(MDD),were investigated.The kinetics and thermodynamics of MDD thermal degradation were analyzed.The results showed that the higher the temperature for heat treatment,the higher the drying rate for Toona sinensis,which was in accordance with the rate changing trend for traditional drying.The MDD degradation process accorded with the first-order kinetics and Arrhenius model.The reactionrate constants ranged from 0.0155 to 0.0345 min^(-1) and increased with an elevated heat treatment temperature.The half-life values(t1/2)at different temperatures were 44.719,32.239 and 20.091 min,respectively,and decreased with an increase of thermal treatment temperature.The activation energy(Ea)value of the reaction was 39.052 kJ/mol.The positive activation enthalpy(ΔH)value indicated that the thermal degradation of MDD was an endothermic reaction,and the positive Gibbs free energy(ΔG)value indicated that MDD thermal degradation was a non-spontaneous process.The results provide a theoretical basis for effective control of the degradation of characteristic flavor substances in Toona sinensis processing process.