Molecular and biochemical effects of anoxia, hypoxia and CO2-enriched atmosphere on Springcrest peaches

Peach fruit (cv “Springcrest”), harvested at commercial maturity stage when flesh firmness was about 60N, were maintained at 20°C in humidified streams of air (control), nitrogen (N2), high (30%) carbon dioxide concentration (CO2), or ultra low (< 1%) oxygen (ULO) up to 96 h. Flesh softening rapidly occurred in control fruit which reached the value of about 10N after 72h. Fruit held in N2 did not show any change in firmness throughout the experimental period, whereas only a slight decrease of this parameter was observed at the end of treatments in ULO- and CO2- treated fruit. Off-flavors were detected at 72 and 96h in all treated fruits. Since oxygen deprivation and/or CO2-enriched atmospheres are known to affect pyruvate metabolism, acetaldehyde and ethanol contents in mesocarp were monitored. In control fruit, acetaldehyde was detected only at 48h and it reached the highest level at 72 and 96h. Altered atmospheres induced an earlier accumulation of the compound after 12h for ULO and CO2, and after 24h for N2. Ethanol content showed an increasing trend in fruit maintained in air during the considered period. Significant increases of ethanol concentration were detected in all treated fruit at 24, 48, 72 and 96h. Alcohol dehydrogenase (ADH) activity was higher than control at 24h in ULO and N2, and at 48, 72 and 96h in all treated samples. Results of a Southern blot carried out with a heterologous probe (pAdhl), indicated that, in peach, ADH is encoded by a multigene family. Transcript analysis carried out at 48h showed that Adh1-related mRNAs were undetectable in fruit flushed with air but clearly accumulated in ULO, N2, and CO2 treated fruit.