Effects of postharvest elicitors on ripening-related metabolic processes of Sangiovese berries

With the aim of better understanding basic processes of Sangiovese berry ripening and considering that postharvest manipulation (to produce special wines as “passiti” and/or reinforced) is now possible in environmentally-controlled dehydration tunnels where specific treatments can be easily performed, trials using two gaseous elicitors (carbon dioxide and ethylene) have been carried out on Sangiovese berries. The effects of CO2 treatment (30% v/v for 3 days followed by storage in air up to 9 days) have been evaluated on flesh and skin separately in terms of both transcript profiling, using the Aros V1 grape microarray (Operon, 14,562 oligos), and polyphenol content. At the end of the treatment and compared with berries at harvest, 214 and 107 targets resulted differentially expressed in the skin and pulp, respectively. This clearly indicates the different metabolic reactivity of the two tissues to environmental stimuli. BLASTX analysis assigned a putative function to 144 (skin) and 107 (pulp) differentially expressed targets. GO categories with the highest number of sequences were: Interaction with the Environment, Cell rescue defence and virulence, Protein with binding function, (primary and secondary) metabolism. Biochemical analyses pointed out that the presence of a CO2-enriched atmosphere after harvest affects polyphenol content: in fact, total phenol and , in particular flavan-3-ols concentration increased in skins of treated berries. These data clearly demonstrate that physiological-metabolic changes occur in Sangiovese berries following the postharvest treatment with CO2: some of these changes might be beneficial in terms of disease control (an important aspect for wine grapes undergoing postharvest dehydration and for the storage of table grapes) and antioxidant properties of the resulting wines. A similar methodological approach has been used for the evaluation of the effects of postharvest ethylene treatments (1000 ppm for 3 days followed by storage in air for 9 days): preliminary analyses pointed out a decrease of pectin content indicating an effect of the hormone on cell wall and on the extractability index. Considering polyphenols, stilbenic compounds (trans-resveratrol) appeared to increase in skins of ethylene-treated berries. This work has been financially supported by the Fondazione Cassa di Risparmio di Pisa.