Thermostability and Browning Development of Fungal α-amylase Freeze-dried in Carbohydrate and PVP Matrices

Abstract

Thermal stability and browning development of systems containing fungal α-amylase in lactose, raffinose, sucrose, trehalose and polyvinylpyrrolidone (PVP) matrices after heat treatment at 70 °C in a constant relative humidity (RH) environment and in connection with phase transitions were studied.Matrices showed considerable variability in their ability to stabilize α-amylase and in browning development. Amorphous trehalose was the most efficient matrix for preventing non-enzymatic browning and thermal inactivation of the α-amylase.Remaining α-amylase activity decreased as RH% and heating time were increased, the extent of the effect being different for each matrix. Trehalose matrix appeared the most efficient in preventing α-amylase deactivation at ‘0’, 11 and 20% RH. At 42% RH all the matrices showed the lowest degree of enzyme stabilization.The matrices' glassy condition was not enough to ensure enzyme thermal stability; the glassy matrices of trehalose and lactose allowed the retention of 80% enzyme activity after 96 h of heat treatment; the remaining activity in raffinose and PVP matrices was 50% or less.The degree of enzymatic activity protection given by different glassy matrices was related to their molecular weight (which affects molecular packing) and to their associated water 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 transition, even in conditions at which trehalose crystallization should occur (42% RH).