Effect of pH on pulsed light inactivation of polyphenol oxidase

Abstract

The inactivation of diverse food enzymes by pulsed light (PL) has been described before, including the inactivation of polyphenol oxidase (PPO) (at pH 6.5). Since the pH affects the conformation of enzymes, it may influence the inactivation of enzymes by PL. The aim of this work was to evaluate the effect of pH on the kinetics of the PL-inactivation and associated structural changes of a case enzyme. To this, PPO was treated by PL at different pHs (4.0-6.5) and its inactivation kinetics and changes in its structure were evaluated by spectrophotometric and spectrofluorometric methods. The inactivation proceeded faster at low pH and was highly correlated with the decrease in peak intrinsic fluorescence intensity. Phase diagrams and parameter A evolution indicated the absence of intermediate unfolded states during the course of the inactivation. No protein aggregation was detected by turbidimetry. Results indicate that although a low pH favors the PL-inactivation of PPO, the mechanism of inactivation is pH-independent. Beyond the specific outcome for PPO, the results are evidence of a general pH-independence in the mechanism of enzyme inactivation by PL in the pH range 4.0-6.5 and acidification can be a strategy to decrease treatment times during PL processing.

Keywords: Enzyme inactivation; Polyphenol oxidase; Pulsed light; Structure-function; pH.