Role of UV-C irradiation scheme on cell wall disassembly and surface mechanical properties in strawberry fruit

UV-C treatments have been reported to prevent firmness loss and decay in part by delaying the degradation of fruit structural barriers. The influence of the irradiation regime on wall disassembly has not been determined. We evaluated the influence of single pre-storage and repeated-low dose UV-C treatments on strawberry mechanical properties and cell wall degradation. Ripe strawberry was subjected to Single-Step UV irradiation (4 kJ m(-2) prior to storage); Two-Step UV irradiation: two 2 kJ m(-2) treatments after 0 and 4 days at 0 degrees C and Multi-Step UV irradiation: five 0.8 kJ m(-2) UV-C applications every 2 days until day 8 at 0 degrees C. A non-irradiated group was used as a control. During storage we determined the changes in surface mechanical properties, hemicellulose and pectin solubility-beta-glucanase-beta-glucosidase, (Glcase) alpha-xylosidase (Xylase), polygalacturonase, (PG); pectin-methylesterase (PME), alpha-arabinofuranosidase (AFase), and beta-galactosidase (beta-gal) activities. UV treated berries showed higher surface hardness and resistance to compression and tolerated greater compression distance to tissue failure. Softening was more effectively reduced in fruit receiving Two-Step and Multi-Step irradiations. Though all UV-C treatments transiently decreased PG, PME and Glcase activities, the improved firmness retention found after Two-Step and Multi-Step irradiation was related to the inhibition of Xylase and beta-gal. Repeated low dose UV exposure prevented softening by delaying pectin solubilization.