Inactivation of polyphenol oxidase using 254Â nm ultraviolet light in a model system

- UV light (254 nm) inactivated tyrosinase (polyphenol oxidase, PPO) activity.
- Conformational changes in protein due to UV exposure cause the inactivation.
- UV induced PPO inactivation was accelerated by presence of fructose and at lower pH.
- UV induced PPO inactivation was decelerated by presence of suspended particles.
- PPO remained inactive during post-processing storage.

Ultraviolet light (254 nm) induced inactivation of mushroom tyrosinase (polyphenol oxidase or PPO) was evaluated. Effect of typical fruit and vegetable juice components such as sugars (glucose, sucrose and fructose at 10 g/100 mL level), pH (3.5-6.8) and suspended particles (844 NTU) on UV induced PPO inactivation was also studied. PPO activity was measured spectroscopically using catechol as a substrate. UV processing was performed in a bench-top, batch scale unit with incident UV intensity of 20 mW/cm2. UV exposure resulted in more than 90% reduction in PPO activity after 5 min of exposure (4.8 J/cm2). PPO inactivation was accelerated by fructose (p < 0.05) due to generation of reactive oxidative species by fructose in presence of UV light. Sucrose and glucose had no effect on the inactivation rate (p > 0.05). PPO inactivation rate was significantly (p < 0.05) higher at pH 3.5 than at pH 6.8 and suspended particles significantly (p < 0.05) reduced the UV induced PPO inactivation due to scattering of UV light. Post-UV processing storage measurements showed that PPO was not reactivated during storage. UV processing can be used to inactivate PPO in fresh produce, albeit the required UV dose may be higher than that needed for a substantial (5-log) reduction in pathogenic microorganisms.