A comprehensive review of segment drying (vesicle granulation and collapse) in citrus fruit: Current state and future directions

• Segment drying, a severe internal physiological disorder of citrus fruit, often occurs during pre- and postharvest storage. • Citrus fruit affected by segment drying exhibit drying taste, flavor loss, and hardened texture. • The relevant metabolic pathways underlying the segment drying are summarized and discussed. • The new hypothesis has been proposed that the disorder of cell wall metabolism may be the main driving factor for segment drying in citrus fruit. Segment drying, a severe internal physiological disorder of citrus fruit, often occurs during pre- and postharvest storage. The disorder deteriorates fruit organoleptic quality, including drying taste, flavor loss, and hardened texture, leading to a loss of edible and marketable value. This study is aimed to comprehensively review the research progress related to segment drying in citrus fruit since the first report nearly 90 years ago. Vesicle granulation and collapse are the two main disorders during segment drying, and the disordered vesicles are highly heterogeneous. We discuss the concept of segment drying, deterioration in fruit quality by this disorder, and the relevant metabolic pathways. The major hypotheses underpinning the occurrence of segment drying are further summarized; herein, we propose the new hypothesis that the disorder of cell wall metabolism in pulp may be the main driving factor for segment drying. We also summarize current methods to prevent segment drying in citrus fruit throughout the whole citrus production chain, including preharvest, harvest, and postharvest periods. Additionally, we propose eight scientific questions to focus on as a vision for future segment drying research.