Influence of short-term postharvest ozone treatments in nitrogen or air atmosphere on the metabolic response of white wine grapes.

Grapes were exposed to ozone gas in air (GO) or in nitrogen atmosphere (GNO) for 12 h at 10 A degrees C and then kept in normal atmosphere for 1 day at room temperature. Grapes kept at 10 A degrees C, for 12 h without ozone treatment plus 1 day at room temperature, were considered as the control sample (GC). Low temperature induced a great change of ripening features only in GC with reduction of weight, loss of sugars (about 20 %) and increase in titratable acidity but, above all, 15 % of increase in malondialdehyde (MDA). The use of ozone in air or in nitrogen neither altered the fruit quality attributes nor modified MDA concentration. Ozone provoked a high decrease of hydroxycinnamic acids, compared to the harvest grapes, overall in GNO samples (caftaric acid -38.8 %; coutaric acid -26.1 %). Cold storage treatment without ozone enhanced antiradical capacity. Three main flavonols, named hyperoside (quercetin-3-O-galactoside), rutin (quercetin-3-O-rutinoside), and kaempferol-3-O-glucoside were found in all grape extracts analyzed, and the total flavonol content increased significantly (p < 0.008) in all the samples starting from 1.79 mg/g dry matter of grapes at harvest (GH sample) up to 2.13 mg/g of GNO one. Both cold storage and ozone in air treatments significantly increased catechin content compared to that in the grapes at harvest (+54.6 and +35.7 % for GC and GO, respectively; p < 0.008). The interrelationships between the parameters analyzed and the different postharvest treatments, as well as the relationships among variables, were investigated by principal component analysis. Component loadings showed significant groupings for concentrations of hydroxycinnamic acid derivates and flavonols, which appeared as good candidates to be further considered as biomarkers of the physiological status of grapes. Similarly, the component scores grouped according to the different postharvest treatments, highlighting hyperoside as a useful indicator of the ozone effect on the grape's physiology.