Glassy state and thermal inactivation of invertase and lactase in dried amorphous matrices

CAROLINA SCHEBOR; LEILA BURIN; MARÍA DEL PILAR BUERA; JOSÉ M. AGUILERA; JORGE CHIRIFE

BIOTECHNOLOGY PROGRESS

Wiley InterScience

Año: 1997 vol. 13 p. 857 - 863

8756-7938

The thermal stability of enzymes lactase and invertase in dried, amorphous matricesof sugars (trehalose, maltose, lactose, sucrose, raffinose) and some other selectedsystems (casein, PVP, milk) was studied. The glass transition temperature (Tg) waslimited as a threshold parameter for predicting enzyme inactivation because (a) enzymeinactivation was observed in glassy matrices, (b) a specific effect of enzyme stabilizationby certain matrices particularly trehalose was observed, and (c) enzyme stabilityappeared to depend on heating temperature (T) “per se” rather than (T - Tg). Forthese reasons, a protective mechanism by sugars related to the maintenance of thetertiary structure of the enzyme was favored. A rapid loss of enzyme (lactase) activitywas observed in heated sucrose systems at T > Tg, and this was attributed to sucrosecrystallization since it is known that upon crystallization the protective effect of sugarsis lost. Thus, the stabilizing effect could be indirectly affected by the Tg of the matrix,since crystallization of sugars only occurs above Tg. Trehalose model systems (withadded invertase) showed an exceptional stability toward “darkening” (e.g., nonenzymaticbrowning) when heated in the dried state to elevated temperatures andfor long periods of time.