Plum Storability Improved after Calcium and Heat Postharvest Treatments: Role of Polyamines

Plums were treated with calcium or heat (45°C) and then stored at 2°C for 28 d. Fruit firmness, ethylene, and CO 2 production rates were investigated. The concentrations of endogenous polyamines (free, conjugated‐soluble, and cell wall‐bound) were also studied. Both treatments improved fruit firmness by increases in Magness‐Taylor force and force‐deformation ratio, and decreases in flesh deformation. No differences were found in either ethylene or respiration rate production among fruits due to the low storage temperature. Calcium‐treating plums increased the conjugated forms of putrescine (conjugated‐soluble and cell wall‐bound), which are related to higher firmness. Heat‐treated plums mainly increased cell wall‐bound spermidine, inducing a greater cell wall stability and plum firmness.