Role of Mono- and Disaccharides on the Inactivation of Peroxidase and Polyphenol Oxidase Induced by Cold Atmospheric Plasma

Polyphenol oxidase (PPO) and peroxidase (POD) are among the most detrimental enzymes in plant-processed foods responsible for enzymatic browning, off-flavors, and loss of bioactive compounds. Among innovative technologies cold atmospheric plasma (CAP) revealed great potential in the inactivation of these enzymes. However, plant foods are complex matrices, and some constituents may counteract the CAP effects. This study investigated the effect of different CAP exposures on the activity of POD and PPO in phosphate buffer and in model systems with different concentrations of monosaccharides (glucose, fructose) and disaccharides (sucrose, trehalose) to evaluate the potential role of sugars in enzyme inactivation. Spectroscopic analyses (fluorescence, circular dichroism, UV-Vis absorption) were conducted to highlight structural modifications possibly accountable for the enzyme inactivation. In buffered systems, the inactivation induced by CAP was dependent on the enzyme, the treatment time, and the ozone concentration in the chamber. Sugars were shown to modify the POD and PPO activity and the enzymes’ ternary and secondary structure to a varying extent depending on their type and concentration. Notably, sucrose and trehalose, especially at the highest concentrations, highlighted a protective effect on the functionality of both proteins. Structural modifications were retained to explain only partially the different protective effects of sugars on HRP and PPO; indeed, other factors, such as the different abilities of sugars to quench plasma reactive species, reduce the system mobility, and stabilize the protein by the hydration shell preservation, possibly played a role in the reduction of enzymes’ inactivation induced by CAP.