Changes in Volatile Compounds During Ripening of West Indian-Type ‘Simmonds' Avocado Treated with Ethylene and Aqueous 1-Methylcyclopropene

Two experiments were conducted to identify volatile compounds during ripening of 'Simmonds' avocado (Persea americana Mill.) and how the volatile composition is affected by exogenous ethylene and 1-methylcyclopropene (MCP) treatments. For Experiment 1, treatments were: C1 - non-treated control; E24 – exogenous ethylene for 24 h at 20 °C; MCP – immersion in aqueous formulation of 1-MCP at 150 µg.L^-1 a.i. for 1 min at 20 °C. In Experiment 2, treatments were: C2 - non-treated control; E12 – exogenous ethylene for 12 h, E12+MCP – exogenous ethylene for 12 h + 12 h air + aqueous 1-MCP at 150 µg.L^-1 a.i. for 1 min. Treatments were applied to mature-green fruit 24 h after harvest and fruit ripening was monitored at 20 °C. Respiration and ethylene production rates were measured daily, while whole fruit firmness was determined every other day. Fruit were considered commercially ripe upon reaching 10 to 15 N firmness at the equator (5-cm dia. flat-plate probe at 2.5 mm deformation). Fruit were assessed for volatile analysis at mature-green, mid-ripe (half of initial fruit firmness) and ripe maturity stages. Volatiles were collected for 1 h from 100 g of diced pulp using a purge-and-trap system and compounds were identified by GC-MS. In Experiment 1, C1-fruit ripened within 7 d. Treatment E24 hastened the onset of the ethylene climacteric peak by 1 d and ripening by 2 d, while MCP delayed both by 2 d. In Experiment 2, C2-fruit ripened in 6 d. Treatment E12 did not hasten the climacteric nor ripening, but E12+MCP delayed both by 2 d. Total volatiles decreased during ripening, most markedly from mid-ripe to ripe stage. The main group of volatiles identified was sesquiterpenes, predominant in mature-green and mid-ripe stages; β-caryophyllene, α-copaene and β-cubebene were the most abundant compounds. Hexanal was also a great contributor to total volatiles. Only a few compounds were detected in ripe fruit; alcohols and aldehydes were predominant and several sesquiterpenes were not detected. Reduced amounts of several compounds and total volatiles were found for MCP-treated fruit when assessed at mid-ripe maturity stage. However, application of exogenous ethylene or 1-MCP did not affect total volatiles in ripe fruit. The additional benefit of shelf-life extension promoted by aqueous 1-MCP treatments corroborates the potential use as a postharvest treatment for the fast-ripening West Indian ‘Simmonds’ avocado.