Volatile profiles of ripening West Indian and Guatemalan-West Indian avocado cultivars as affected by aqueous 1-methylcyclopropene

Abstract

Separate experiments were conducted with three major commercial avocado (Persea americana Mill.) cultivars grown in Florida: ‘Simmonds’ (early-season, West Indian race); ‘Booth 7’ (mid-season, Guatemalan-West Indian hybrid); and ‘Monroe’ (late-season, Guatemalan-West Indian hybrid). Fruit were harvested at preclimacteric stage and left untreated (Control) or treated 24h after harvest with aqueous 1-methylcyclopropene (1-MCP) at 1.39 (treatment M1) or 2.77μmolL−1 a.i. (treatment M2) (75 or 150μgL−1) for 1min at 20°C. Whole fruit ripening was monitored at 20°C/92%±3% R.H. and based on whole fruit firmness, respiration and ethylene evolution. Fruit volatiles were assessed at preclimacteric (24h after harvest), mid-ripe (half of initial fruit firmness) and ripe maturity stages, from 100g of chopped pulp using a purge and trap system. Untreated, firmer fruit ‘Monroe’ (268N at harvest) ripened within 12 d of harvest while softer fruit ‘Simmonds’ (118N) ripened within only 6 d. 1-MCP treatment extended ripening time from 33% (M1) to 83% (M2). All fruit softened normally, indicating the potential benefits of aqueous 1-MCP as a postharvest treatment for avocado when applied at these concentrations. Volatile profiles differed among the three cultivars with several compounds detected in only one cultivar, results that may contribute to a potential identification of the origin of the cultivar based on fruit volatile composition. The West Indian cultivar ‘Simmonds’ had much higher emission of hexanal (preclimacteric fruit) and cis-3-hexenal and cis-3-hexen-1-ol (ripe fruit) than the Guatemalan-West Indian hybrids ‘Booth 7’ and ‘Monroe’. On the other hand, these latter hybrids had much higher levels of alkanes than ‘Simmonds’. Treatment with 1-MCP increased emissions of alkanes during ripening of ‘Booth 7’ and ‘Monroe’. Total volatiles of avocado decreased during ripening mainly due to the significant reduction of sesquiterpenes, the main group of volatiles in all cultivars at harvest (‘Simmonds’, 53%; ‘Booth 7’, 78%; ‘Monroe’, 66%). β-Caryophyllene was the major compound at harvest, but decreased to less than 2% in ripe fruit, at which point most sesquiterpenes were not detected. Among the 10 sesquiterpenes commonly found in the avocado cultivars in this study, only α-Copaene had significantly higher emissions in mid-ripe fruit treated with the higher concentration of 1-MCP (2.77μmolL−1 a.i.), suggesting that ethylene participates in the regulation of this sesquiterpene.