中、碱性条件下L-抗坏血酸自降解非酶褐变过程动力学研究

Self-degradation reaction kinetics of L-ascorbic acid under neutral and alkaline condition

在中、碱性溶液环境下,对L-抗坏血酸自降解过程非酶褐变反应的化学行为进行了研究。考察了反应温度、时间、pH等对L-抗坏血酸自降解过程的影响,包括对底物消耗、无色中间体及褐色物质生成的影响;分析探讨了褐色物质生成的动力学特征。结果表明:反应体系温度越高,时间越长,溶液越偏向碱性环境,越有利于L-抗坏血酸的自降解及无色中间体和褐色物质的生成。生成褐色物质动力学研究表明:褐色物质的生成只与L-抗坏血酸的降解有关;通过建立褐色物质生成动力学方程发现,褐色物质的生成符合准零级动力学特征。不同pH环境,生成褐色物质的活化能不一样。当溶液pH值为9.5时,褐色物质的生成活化能为27.62kJ·mol^-1,均小于其它pH值下的生成活化能。根据L-抗坏血酸降解过程,对L-抗坏血酸降解机理进行了探讨,提出了在中、碱性条件下可能的降解机理。

The kinetic characteristics of non-enzymatic browning reaction about the self-degradation of L-ascorbic acid(ASA)were investigated in neutral and alkaline solutions.The influences of temperature,time and pH on formation of uncolored-intermediate-products(UIPs)and brown-products(BPs)were studied.The kinetic formation characteristics of BPs were also discussed.The results showed that the higher temperature,the longer time and the stronger the alkali of the solution,the more favorable for the self-degradation of ASA and the formation of UIPs and BPs.The kinetics studies had shown that the formation of BPs was only related the self-degradation of ASA.The formation kinetics model of BPs was established,which showed that the formation of BPs was consistent with pseud-zero-order kinetics.Surrounding in the different pH conditions,the activation energy(Ea)of BPs was different.When the pH value was 9.5,the E a for formation of BPs was 27.62 kJ·mol^-1 ,which was less than those other pH solution.The self-degradation mechanism of ASA was discussed and its possible degradation mechanism was proposed according to the degradation process of ASA.