A biochemical and molecular dissection of the response induced by postharvest UV-B radiation on quality traits of peach fruits

In the present study the possibility of enhancing the content of health-promoting compounds of peaches and nectarines (Prunus persica L. Batsch) by post-harvest irradiation with UV-B was assessed. Moreover, the impact of UV-B on the cell wall metabolism of peach fruits was also investigated. Fruits of ‘Suncrest’ (Melting flesh-type, MF) and ‘Babygold 7’ (Non-Melting flesh-type, NMF) peach and ‘Big Top’ nectarine (Slow Melting flesh-type, SM) cultivars were firstly irradiated with UV-B (1.69 W/m2) for 12 h, 24 h and 36 h. A photosynthetic photon flux density of 500 μmol m-2 s-1 was provided. Control fruits underwent the same conditions but UV-B lamps were screened by benzophenone-treated polyethylene film. Subsequently, fruits of ‘Suncrest’ and ‘Big Top’ cultivars, which showed a positive response to the UV-B radiation, were subjected to a second different experiment providing 24 h of irradiation after which treated and control fruits were stored up to 36 hours at 10 °C. The effectiveness of the UV-B treatment in modulating the concentration of phenolic compounds and ascorbic acid was cultivar-dependent. ‘Big Top’ and ‘Suncrest’ fruits were generally affected by increasing health-promoting compounds whereas in ‘Babygold 7’levels of secondary metabolites decreased after UV-B irradiation. A corresponding trend was exhibited by most of phenylpropanoid biosynthetic genes which were tested by qRT-PCR. In MF-type fruits, UV-B radiation slowed down the softening process and reduced the flesh firmness loss. This evidence was attributed to the inhibition of expansin synthesis, regulated at gene level by UV-B. The UV-B treatment did not induce differences in flesh firmness between control and treated fruits of NMF and SM fruits. After 36 h of storage at 10°C, fruits treated with UV-B exhibited generally higher contents of antioxidant compounds. In both experiments, the concentration of phenolic compounds and ascorbic acid were correlated with the accumulation of radicals measured by EPR analysis. Based on these results UV-B irradiation can be considered a promising technique to increase the health-promoting potential of peach fruits at the same time improving shelf-life and quality.