Evaluation of natural extracts as potential enzymatic browning inhibitors

Enzymatic browning in fruits represents a difficult problem for Food Industry, especially with recent restrictions in the use of synthetic antioxidants. It is often associated with undesirable off-flavors and negative effects on taste and nutritional value. This physiological disorder is mainly due to the oxidation of natural phenolic compounds into quinones that are polymerized to brown pigments by polyphenol oxidase (PPO). Peroxidase (POX) is also alleged to be related to browning development, by inducing H2O2 oxidation of phenolic compounds. Prevention of browning reactions, catalyzed by these enzymes, has traditionally been accomplished by various chemicals, as ascorbic and citric acids. Partial control of this disorder can be obtained with the application of antioxidants, which compete with common substracts for the enzymatic activity. This study assessed the potential of natural extracts, with antioxidant properties (such as soy protein concentrate, extracts of apple byproduct and olive leaves) as novel enzymatic browning inhibitors. The antioxidant capacity was assessed by the radical scavenging assay using ABTS+ radical. The natural extracts inhibitory effect on PPO and POX activity was evaluated using a spectrophotometric assay by reaction of the natural extracts with the pure enzymes, using catechol and guaiacol as substrates, respectively. The present study demonstrated that olive leaves had the highest antioxidant capacity (2.688 ± 0.006 mg/mL TEAC equivalent), however, apple byproduct was the most effective on PPO and POX activity inhibition. The study has practical implications in generating novel natural extracts with potential application as anti-browning agents.