Cytological and metabolomic analysis of Citrus fruit to elucidate puffing disorder

Puffiness, a physiological disorder commonly observed during the ripening and post-harvest processes of fruits in Citrus reticulata, significantly affects the quality and shelf-life of citrus fruits. The complex array of factors contributing to puffiness has obscured the current understanding of its mechanistic basis. This study examined the puffing index (PI) of 12 citrus varieties at full ripeness, focusing on the albedo layer as a crucial tissue, and investigated the correlation between cellular structural characteristics, key primary metabolites and PI. The findings revealed that the cell gap difference and the number of lipid droplets were closely linked to PI. Chlorogenic acid, Ferulic acid, D-Galacturonic acid, D-Glucuronic acid, (9Z,11E)-Octadecadienoic acid, and 9(10)-EpOME were identified as pivotal primary metabolites for rind puffing. Determination of lignin, protopectin, cellulose and lipoxygenase content further validated the relationship between cell wall, lipid metabolism and rind puffing. This study furnishes novel insights into the mechanisms underlying puffing disorder.