Solid-state tyrosinase stability as affected by water activity and glass transition

The effects of water activity (a(w)) and the state of the system as dictated by the glass transition temperature (Tg) on tyrosinase storage stability were evaluated in a model food system. Tyrosinase was incorporated into low and high molecular weight polyvinylpyrrolidone (PVP-LMW and PVP-K30, respectively). Samples were equilibrated and stored in desiccators from a(w) 0.33 to 0.77 at 20 degrees C. Tyrosinase activity was monitored for a week, and pseudo-first order rate constants for activity loss were calculated. Residual activity after equilibration correlated with T-g rather than a(w). An apparent rate constant increase slightly above T-g was observed and rate constants were the same at constant T-g, suggesting that molecular mobility as dictated by T-g was influencing tyrosinase storage stability. (C) 2000 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.