Color loss in ethanolic solutions of chlorophyll a.

The present study investigated the stability of green color in 1-60% ethanolic solutions of chlorophyll a. Kinetics studies were performed. The results show that the color loss follows first-order reaction kinetics, similar to that in aqueous systems, with a reaction rate constant between 0.013 and 13.575 day(-1) at 20 degrees C and an activation energy between 18.4 and 85.1 kJ mol(-1). The rate of color loss increases with the temperature and varies with the ethanol concentration. It reaches the maximum at 40% ethanol concentrations. The difference among the absorption spectra of the ethanolic solutions suggests that the interaction between water and ethanol molecules may be the major factor affecting the color stability of chlorophyll in the solutions. The bathochromic shift is most obvious around 40% ethanol concentration. We postulate that the formation of clusters of water-ethanol molecules is responsible for the increase in the rate of color loss.