The combined thermal (25-65°C) and ultraviolet processing (UV-C) effects on lipoxygenase (LOX), peroxidase (POD) and polyphenoloxidase (PPO) at different pH values (4.0-7.0) were studied using a central composite design. An initial screening design revealed that all factors had a significant effect on enzymatic activity except wavelength which showed a negligible effect. A synergistic effect was found between temperature and UV exposure time for POD and PPO and between pH and exposure time for LOX. LOX enzyme was affected by acidic conditions. POD was UV-C labile whereas PPO was the most UV-C resistant enzyme but was thermolabile. Second-order polynomial equations indicated that enzyme activities were inactivated after exposure to 58.2mJ/cm2 UV at 60°C or higher temperatures at any pH condition. Combination of UV and thermal processing allowed the use of low energy/doses to obtain complete enzymatic inactivation. This study may serve as a basis to design UV-C processes for the inactivation of enzymes in liquid matrices.
Bibliographical noteFunding Information:
The authors are grateful to the Fundación Española para la Ciencia y la Tecnología (FECYT) from Ministerio de Innovación y Ciencia from Spain for providing the postdoctoral grant to Dr. Fernando Sampedro. The authors acknowledge Drs. Gerald Sapers and James Smith for their helpful review of the final draft. The authors also want to acknowledge Drs. Lihan Huang and Kathleen Rajkowski, Ms. Jennifer Cassidy and Ms. Kimberly Sokorai for providing technical assistance with the UV unit and the analytical methods.
- Central composite design