Effect of heat treatments on gene expression and enzyme activities associated to cell wall degradation in strawberry fruit

Strawberries at white ripening stage were heat treated at 45 °C for 3 h in an air oven and then stored at 20 °C for 72 h. Firmness, activity of enzymes associated to cell wall degradation, and expression of related genes were determined during the storage. Fruit firmness decreased during the incubation time, and after 24 h of storage the heat-treated fruit softened less than the control fruit. However, after 3 days at 20 °C no differences in firmness were detected between control and heat-treated fruit. Immediately after heat treatment application, the activity of endo-1,4-β-d-glucanase (EGase), β-xylosidase and β-galactosidase decreased, while polygalacturonase activity remained at a level similar to the control fruit. However, lower activities of all these enzymes, including polygalacturonase, were detected in heat-treated fruit after 24 h at 20 °C. The enzyme activity of β-xylosidase, β-galactosidase and polygalacturonase increased after 72 h up to similar or higher values than those of controls. However, endo-1,4-β-d-glucanase activity remained lower in heat-treated samples even after 72 h at 20 °C. The expression of genes encoding endoglucanase (FaCel1), β-xylosidase (FaXyl1), polygalacturonase (FaPG1) and expansin (FaExp2) was reduced immediately after treatment and during the following 4 h, and then increased after 24 h to levels similar to or higher than those of control fruit.Therefore, the selected treatment (45 °C, 3 h in air) effectively reduced strawberry softening and caused a temporary reduction of both the expression of above-mentioned genes and the activity of a set of enzymes involved in cell wall disassembly.