Retention of β-galactosidase activity as related to Maillard reaction, lactose crystallization, collapse and glass transition in low moisture whey systems

Retention of beta-galactosidase activity was analyzed in whey model systems in relation to browning development and physical characteristics of the matrix (degree of matrix compression, crystallinity, glass transition). Amorphous systems were obtained by freeze-drying solutions containing beta-galactosidase and reduced lactose milk whey, with or without maltodextrin. Samples (porous or previously compressed) were exposed to atmospheres of relative humidities of 0%, 22% or 44% and stored at 70degreesC. Remaining enzymatic activity and color development were determined at selected time intervals. The decrease of enzyme activity was simultaneous to browning development, which was in turn accelerated in the low porosity samples and affected by the glass transition of the systems and lactose crystallization. The addition of maltodextrin improved retention of enzyme activity and delayed both browning development and lactose crystallization. (C) 2003 Elsevier Ltd. All rights reserved.