α-Farnesene, conjugated Trienols, fermentative metabolites and superficial scald in 'conference' pears as affected by 1-methylcyclopropene, initial low oxygen stress and controlled atmosphere storage

The effect of initial low oxygen stress (ILOS) on α-farnesene, conjugated trienols (CTols), fermentative metabolites and superficial scald development in ‘Conference’ pears was investigated. At harvest, fruit were untreated or treated with 300 ppb 1-MCP. After 4 weeks at -0.5°C, fruit were stored up to 13 weeks in controlled atmosphere (CA, 2 kPaO2 + 0.7 kPaCO2) with or without ILOS (0.3-0.5 kPaO2) or in air (NA) at -0.5°C. ILOS was applied for 2 weeks either one time (ILOS1) or twice at 3 weeks interval (ILOS2), while monitored with fluorescence sensors (HarvestWatchTM). α-farnesene, CTols and fermentative metabolites were measured at the beginning and at the end of ILOS1 and ILOS2 in comparison with NA and CA storage and after 13 weeks of storage. Scald incidence was evaluated at the end of storage after 7 days at 20°C. Fluorescence monitoring indicated that in order to achieve the low oxygen stress in ‘Conference’ pears, O2 has to be kept lower than 0.4 kPa in control fruit, and that 1-MCP treatment lowered the low O2 limit. As in ILOS1 containers O2 did not drop below 0.4 kPa, ILOS1 pears have not undergone any stress, as confirmed by the trends of fermentative metabolites, α-farnesene and CTols, which did not differ from the CA stored fruit. In ILOS2 there was lower α-farnesene and CT268 than in CA and NA, coupled to an increase in ethanol production. On average, fruit treated with 1-MCP had lower α-farnesene and CTols than untreated pears. α-Farnesene, CTols and ethyl acetate increased and acetaldehyde and ethanol decreased with storage. Storage atmosphere did not influence α-farnesene and CTols, but affected acetaldehyde and ethanol contents in the pulp, with CA, ILOS1 and ILOS2 stored fruit being characterized by lower amounts of acetaldehyde, and higher quantities of ethanol than NA stored pears. In all storage conditions, untreated fruit developed brown scald, with NA fruits having the highest incidence and severity. 1-MCP treated fruit developed some scald in in all storage regimes, but less than untreated ones. ILOS2 pears showed the highest percentage of healthy fruits, irrespective of 1-MCP treatment. Our results indicated that, even if stress was obtained in ILOS2 storage, a clear correlation between α-farnesene, CTols and brown scald development was not found. However, ILOS2 fruit, having less α-farnesene and fermentative metabolites, showed the lowest percentage of scald.