[A study on the decomposition kinetics of vitamin C powder].

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 of Kc of vitamin C powder is: kc = 'exp (-Ea/RT) exp (m 'RH), where k' and m' are constants, RH is relative humidity and Ea is activation energy, when RH less than 70%, Ea = 104.33 kJ . mol-1. The degradation curve of vitamin C powder under various temperatures and humidities can be expressed by C = N/(1 + Btn), the rate equation of degradation of vitamin C powder is: -dC/dt = kdC(1 + 1/n) (N-C)(1 - 1/n), where kd 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 202.64 kJ.mol-1, respectively.