Potential Metabolic Pathways and Related Processes Involved in Pericarp Browning for Postharvest Pomegranate Fruits

Abstract

Pericarp browning occurs widely in postharvest pomegranate fruit, but little is known about its mechanism. In this study, ‘Baiyushizi’, a browning-sensitive cultivar, was used to investigate the physiological and genetic changes during pericarp browning. The pericarp browning index (BI) increased greatly after 3 d storage at room temperature, and, consequently, the fruit appearance became unattractive after 6 d. The increasing concentration of malondialdehyde (MDA) and electrolyte leakage were detected in browning pericarp. Polyphenol oxidase (PPO) activity increased significantly after 3 d, while ascorbate peroxidase (APX) and catalase (CAT) activity decreased steadily during storage. Total phenolics content decreased gradually during storage, while ascorbic acid (AsA) and glutathione (GSH) contents increased firstly, then declined. Differentially expressed genes (DEGs) of pericarp under different browning degrees were identified in the metabolic processes of phenolic compounds, lipids, ascorbic acid, glutathione, sugar, starch, energy-related, ethylene biosynthesis and signal transduction pathways. Accordingly, the potential metabolic pathways and related processes involved in pericarp browning were described. The results not only provided insights on the genetic mechanism of pericarp browning in pomegranate but also guidance on controlling postharvest fruit browning in general.