Heat Treatments Delay Ripening and Postharvest Decay of Strawberry Fruit

Fully red strawberries ( Fragaria × ananassa Duch. cv. Selva) were treated for 1−5 h at temperatures ranging from 39 to 50 °C. After treatments, fruits were placed at 0 °C overnight and then held at 20 °C for 3 days. Most of the heat treatments improved strawberry shelf life, with best results obtained for fruit heated at 42 °C and 48 °C for 3 h. Heat treatments prevented fungal development and decreased the number of damaged fruits. These treatments were then used to treat strawberries at 50−75% red to analyze effects on firmness, surface color, anthocyanin content, PAL activity, polypeptide composition, and protein synthesis. Softening rate and external color development was less in fruit heated at 48 °C compared to the control, while treatment at 42 °C did not significantly affect these parameters. However, both treatments reduced anthocyanin accumulation and PAL activity relative to the controls. In addition, treatment at 48 °C for 3 h reduced protein synthesis, but this effect was partially reversed after holding fruits at 20 °C for 48 h. Heat treatments (42 and 48 °C) led to the accumulation of five heat shock proteins of 88, 76.5, 69, 19, and 17 kDa. In addition, treatment at 42 °C induced the synthesis of a 22 kDa polypeptide that was not observed in the 48 °C treatment. Fruits treated at 48 °C continued the synthesis of 69, 19, and 17 kDa polypeptides even after 48 h at 20 °C. According to these results, the lower fungal development and the slower ripening rate shown by heat-treated fruits suggest that this physical method could be useful to extend the postharvest shelf life of strawberry.