Metabolomics Study at the Postharvest Conditions of Cold Storage and Fungicide (Imazalil Sulfate) Treatment in Navel Oranges and Clementine Mandarins

Millions of citrus products are wasted every year due to postharvest fungal infections. To minimize fungal infections, packhouses utilize aqueous applications of fungicides to prevent infections that occur during harvest. The most prominent fungal pathogens of citrus fruit are commonly treated with imazalil sulfate (IMZ) due to its efficacy for controlling these pathogens at low cost and ease of handling. However, little is known on how it alters the tissues in the citrus fruit physiology. In this study, a nuclear magnetic resonance (NMR)-based metabolomics study is utilized to investigate the role of IMZ treatment in the juice, albedo, and flavedo tissues of two citrus commodities (navels and clementines). The experimental design consists of (a) fresh fruits at harvest, (b) raw fruits stored at 4 °C for 10 days, and (c) raw fruits treated with IMZ and stored at 4 °C for 10 days. Twenty-seven metabolites were identified, and several changes of metabolite composition due to either cold storage or IMZ treatment for both the spatial (albedo, flavedo, or juice) and temporal levels (days and storage) were found. The results show a notable difference between metabolomics profiles across the types and tissues, particularly significant changes on the albedo tissues of clementine. Furthermore, the pathways derived from the metabolomics profiles of the cold storage and the IMZ treatment are complementary to each other. Thus, the utility of metabolomics as a quality control tool in the citrus industry has the potential for broader applications to understand fruit growth and development.