DIFFERENTIATING BETWEEN THE EFFECTS OF WATER ACTIVITY AND GLASS-TRANSITION DEPENDENT MOBILITY ON A SOLID-STATE CHEMICAL-REACTION - ASPARTAME DEGRADATION

Recent debates have emerged on whether it is water activity (alpha(w)) or the state of the system as dictated by the glass transition temper ature (T-g) that impacts the rates of chemical reactions in reduced-mo isture solid systems. Previously, model systems could not evaluate the effects of water activity and glass transition independently. By usin g poly(vinylpyrrolidone) (PVP) of different molecular weights, the eff ect of water activity and glass transition on chemical reactions can b e studied independently and at a constant temperature. The kinetics of aspartame degradation, via its rearrangement into diketopiperazine, w as evaluated in the PVP model system. Reaction rates at constant water activity, but different T-g values, were not significantly different. However, rates at a similar distance from T-g, but different water ac tivities, were significantly different. Thus, the rate of aspartame de gradation depends upon the water activity rather than upon the state o f the system.