THERMOSTABILITY AND BROWNING DEVELOPMENT OF FUNGAL ALPHA-AMYLASE FREEZE-DRIED IN CARBOHYDRATE AND PVP MATRICES

Thermal stability and browning development of systems containing funga l cr-amylase in lactose, raffinose, sucrose, trehalose and polyvinylpy rrolidone (PVP) matrices after heat treatment at 70 degrees C in a con stant relative humidity (RH) environment and in connection with phase transitions were studied. Matrices showed considerable variability in their ability to stabilize alpha-amylase and in browning development. Amorphous trehalose was the most efficient matrix for preventing non-e nzymatic browning and thermal inactivation of the alpha-amylase. Remai ning alpha-amylase activity decreased as RH% and heating time were inc reased, the extent of the effect being different for each matrix. Treh alose matrix appeared the most efficient in preventing alpha-amylase d eactivation at '0', 11 and 20% RH. At 42% RH all the matrices showed t he lowest degree of enzyme stabilization. The matrices' glassy conditi on was not enough to ensure enzyme thermal stability; the glassy matri ces of trehalose and lactose allowed the retention of 80% enzyme activ ity after 96 h of heat treatment; the remaining activity in raffinose and PVP matrices was 50% or less. The degree of enzymatic activity pro tection given by different glassy matrices was related to their molecu lar weight (which affects molecular packing) and to their associated w ater content. The degree of browning in each matrix did not follow the same pattern as loss of enzymatic activity. Browning in trehalose and PVP systems was minimal and not accelerated above the glass transitio n, even in conditions at which trehalose crystallization should occur (42% RH). (C) 1998 Academic Press Limited.