Effect of Cinnamon Essential Oil Nanoemulsion Combined with Ascorbic Acid on Enzymatic Browning of Cloudy Apple Juice

Enzymatic browning seriously influenced the color and nutrition of fruits and vegetables. This study investigated the effect of cinnamon essential oil nanoemulsion (0.1, 0.2, and 0.4%) combined with 0.05% ascorbic acid (AA) on polyphenol oxidase (PPO) activity and related quality of cloudy apple juice. Cinnamon essential oil nanoemulsion was stable in the presence of AA with different concentrations. The individual cinnamon essential oil nanoemulsion showed 80–90% inhibition of PPO activity, which is not enough to effectively control the browning of apple juice. When the cinnamon essential oil nanoemulsion was combined with 0.05% AA, the cinnamon essential oil nanoemulsion acted as a PPO inhibitor and AA acted as a reducing agent, which completely inhibited PPO activity and preserved the color of apple juice during 48 h of storage at 4 °C. In addition, 0.2% and 0.4% cinnamon essential oil nanoemulsion combined with AA reduced the instability index of apple juice from 0.473 to 0.034 and 0.018, respectively. Furthermore, the combined treatment delayed the degradation of total phenol and AA content in apple juice. Collectively, these results indicated that the combination of cinnamon essential oil nanoemulsion and AA could be used to enhance the inhibition of enzymatic browning and maintain the quality of cloudy apple juice.