Role of methyl jasmonate in enhancing pigmentation of Tarocco Sant'Alfio (Citrus sinensis [L.], Osbeck) oranges during cold storage

The aim of study was to evaluate the effectiveness of postharvest methyl jasmonate (MeJA) treatment in enhancing flesh pigmentation and quality in the red orange cv. Tarocco Sant'Alfio, a cultivar known for its late ripening time and limited natural anthocyanin accumulation. Moreover, we tested an image analysis methodology to understand the dynamic of tissue pigmentation and, eventually, we investigate the specific role of individual anthocyanins. Oranges were treated with 0.1 mM MeJA and stored at 8 °C for 28 days. Weekly during storage, physical and organoleptic fruit traits as well as anthocyanins amount and composition, and bioactive compound, were measured. MeJA-treated fruit developed a significantly more intense and earlier red colouration than untreated fruit and exhibited a significantly lower weight loss. Image analysis of the flesh pigmentation gave a valuable insights into the effects of postharvest treatments and the dynamics of pigment accumulation, revealing a marked shift from low to high-intense red distributions in MeJA-treated fruit, in line with the spectrophotometric and HPLC-based anthocyanin quantification. Regression analyses showed that cyanidin 3- O -(6”-dioxalyl)-glucoside, peonidin 3- O -(6”-malonyl)-glucoside, cyanidin 3- O – glucoside, cyanidin 3- O -sophoroside and cyanidin derivatives, were the main contributors to colour development, with moderate to high correlation coefficients with R² ranging from 0.71 to 0.78, confirming the key role of specific anthocyanins in the observed pigmentation dynamics. These findings underscore the potential of MeJA as an effective postharvest treatment to enhance both the visual appeal and nutritional value of blood oranges with naturally low pigmentation.