Deactivation kinetics and the effects of additives on storage stability and structure of D-psicose 3-epimerase.

OBJECTIVE: To explore deactivation kinetics and the effects of some additives on the activity and conformational changes of D-psicose 3-epimerase (DPEase) during its storage.

RESULTS: The experimental data of DPEase inactivation during storage at 4-45 °C fitted with the first-order expression model. The inactivation rate constants of DPEase stored at 4, 10, 25, 35 and 45 °C were 0.0076, 0.01, 0.0223, 0.0351 and 0.0605 day, respectively. A regression formula of half-lives as storage temperatures, ln t 1/2  = 4.7396/T × 103  - 12.536, was obtained. MnSO4 at 0.15 g l-1 enhanced the residual activity by 16% after 15 days and 17% after 30 days compared with control, but 2 g ascorbic acid l-1 reduced activity by 69 and 58% at the same time. In addition, 0.15 g MnSO4 l-1 and 20 g ethylene glycol l-1 maintained the secondary and tertiary structure of DPEase.

CONCLUSIONS: MnSO4 and ethylene glycol actively promoted the storage and conformational stability of DPEase. In contrast, ascorbic acid was disadvantageous.