Heat treatments delay ripening and postharvest decay of strawberry fruit

Fully red strawberries (Fragaria x ananassa Duch. cv. Selva) were treated for 1-5 h at temperatures ranging from 39 to 50 degrees C. After treatments, fruits were placed at 0 degrees C overnight and then held at 20 degrees C for 3 days. Most of the heat treatments improved strawberry shelf life, with best results obtained for fruit heated at 42 degrees C and 48 degrees 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 degrees C compared to the control, while treatment at 42 degrees 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 degrees C for 3 h reduced protein synthesis, but this effect was partially reversed after holding fruits at 20 degrees C for 48 h. Heat treatments (42 and 48 degrees C) led to the accumulation of five heat shock proteins of 88, 76.5, 69, 19, and 17 kDa. In addition, treatment at 42 degrees C induced the synthesis of a 22 kDa polypeptide that was not observed in the 48 degrees C treatment. Fruits treated at 48 degrees C continued the synthesis of 69, 19, and 17 kDa polypeptides even after 48 h at 20 degrees 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.