维生素C粉末分解动力学研究

A STUDY ON THE DECOMPOSITION KINETICS OF VITAMIN C POWDER

在有氧避光条件下,用恒温恒湿加速试验法,研究了在相对湿度小于临界相对湿度时,维生素C粉末的表观变色速率常数k_C与温度、湿度的关系为:k_C=k′exp(-E_a/RT)exp(m′RH),k′与m′为常数,RH为相对湿度,E_a为活化能。RH<70％时的E_a=104.33 kJ·mol^(-1)。还研究了在各种相对湿度下维生素C粉末含量变化的曲线方程为:C=N/(1+Bt^n),速率方程为:k_d为分解反应的表现速率常数,N为原始百分含量,C为时间t的含量,B与n为常数。RH为97,93与79.5％时的E_a分别为86.87,88.22与202.64 kJ·mol^(-1)。

The effect of temperature and humidity on the discoloration and degradation of vitamin C powder was studied via accelerated test under isothermal and constant humidity conditions. The changes of color and concentration of vitamin C were monitored by diffuse reflectance spectroscopy and iodimetry respectively. Under the condition of relative humidity less than the critical relative humidity, the apparent rate constant of discoloration k_c of vitamin C powder is: k_c=kéxp (-Ea/RT)exp (m'RH ), where k' and m'are constants, RH is relative humidity and E_a is activation energy, when RH<70%, E_a=104.33 kJ·mol^(-1). The degradation curve of vitamin C powder under various temperatures and humidities can be expressed by C=N/(1+Bt^n), the rate equation of degradation of vitamin C powder is:-d C/dt =k_dC^(1+1/n) (N-C)^(1-1/n), where k_d is the apparent rate constant of degradation, B and n are constants, N is the initial content of vitamin C and C is the content of vitamin C at time t. When RH are 97,93, and 79.5%, Ea are 86.87,88.22 and 202.64kJ·mol^(-1), respectively.