DRYING OF ENZYMES - ENZYME RETENTION DURING DRYING OF A SINGLE DROPLET

A single suspended droplet (initial diameter, d(p) is approximately equal to 2 mm) of sugar solutions containing beta-galactosidase, glucose oxidase or alkaline phosphatase was dried at a constant air temperature. The average moisture content u(a), drop temperature T(d) and the relative remaining enzyme activity X(E) were measured as a function of drying time. Separate experiments were done for determining the inactivation rate k as a function of the water content u and temperature T. By using the k(u, T) data together with the water diffusivity and the water activity reported previously, we calculated the u(a)-t, T(d)-t and X(E)-t relations and compared with the experimental ones. The calculated and experimental results showed that lower air temperature and smaller droplets give a higher enzyme retention. The foamed droplets also resulted in a high retention. The enzyme retention was also strongly influenced by the type of dissolved sugars and oxidation. When an appropriate dissolved solid was chosen, the whole enzyme activity was found to be retained even at air temperature above 80-degrees-C.