Kojic acid: evaluation of its effectiveness in controlling pulp browning in minimally processed ‘Royal Gala’ apples

Minimally processed apples (MPA) are tasty, easy to consume, nutritious (sugars, vitamins and minerals) and functional (dietary fiber and secondary metabolites such as flavonoids, isoflavonoids, carotenoids and phenolic acids). However, following processing, pulp browning rapidly compromises its natural color, texture, flavor, and health benefits. To deal with this problem, refrigerated storage combined with antioxidant treatment is usually employed. In this study, kojic acid (KA), a metabolite of fungi ( Aspergillus and Penicillium ) widely used as a food additive to prevent enzymatic browning and bacterial growth, was used as an antioxidant. It was tested at three different concentrations (0.03%, 0.05% and 0.07%) in minimally processed ‘Royal Gala’ apples, for up to 9 days of cold storage. Distilled water and 0.6% L-cysteine chloride were used as negative and positive controls, respectively. Browning index, Hue angle, antioxidant activity, total phenolic compounds, enzyme activity (peroxidase and polyphenoloxidase) and sensory attributes were evaluated. The browning of ‘Royal Gala’ apples was dependent on KA concentration for all related variables (L*, a* e b*, Hue angle and browning index). KA at concentrations of 0.05% and 0.07% showed results similar to the positive control (L-cysteine). The values of total phenolic compounds and antioxidant activity were stable for apples treated with KA 0.07% during the 9 days of storage. The peroxidase activity of apples treated with KA 0.07% was similar to that of apples treated with L-cysteine 0.6%. Sensorial analysis showed that KA-treated apples scored better than L-cysteine-treated apples. KA 0.07% was effective in controlling the browning of ‘Royal Gala’ apple pulp, without altering the sensory characteristics during the 9 days of refrigerated storage.