Chlorine Dioxide Delays Enzymatic Browning in Postharvest Cherimoya and Enables Establishment of Kinetics Substrate Model

Abstract

Cherimoya (Annona squamosa L.) is a nutrient-rich fruit. However, it is not easy to store because of its susceptibility to browning. In order to prolong the storage period of cherimoya, the fruit was treated with chlorine dioxide (ClO2) at different concentrations (20, 40, 60, 80, and 100 mg L−1) and stored at 15 °C for 8 days. The quality and biochemical indexes of the fruit were investigated using a chromameter, high-performance liquid chromatography and scanning electron microscopy, etc. The results showed that all the treatments with various concentrations of ClO2 could delay the increase in the browning index, loss of weight, and decrease in hardness. Meanwhile, ClO2 treatment effectively reduced the consumption of starch, titratable acids, and phenolics as well as inhibited the polyphenol oxidase (PPO) activity and enzymatic oxidation. It can be seen from the Fourier transform infrared spectrum (FTIR) that the C=O stretching peak at 1731 cm−1 disappeared at a ClO2 concentration of 60 mg L−1. We think the ClO2 treatment may inhibit the oxidation of phenol to quinone. According to the Arrhenius formula, the values of the apparent activation energy (Ea) for enzymatic browning reaction were estimated. The Ea with catechol in cherimoya pericarp and flesh were 67.00 and 47.83 kJ mol−1, respectively. It was found that the phenolic enzyme reaction with catechol has a much smaller Ea and a higher affinity for PPO. Therefore, treatment with ClO2 at a suitable concentration for cherimoya stored at 15 °C could effectively maintain fruit quality and prolong the storage period; the most appropriate concentration is 60 mg L−1.