Postharvest ethylene and 1-MCP treatments both affect phenols, anthocyanins, and aromatic quality of Aleatico grapes and wine

Abstract

Aleatico grapes (Vitis vinifera L. cv. Aleatico) picked at 20.4–20.6oBrix were treated with air containing 500 mg/L ethylene for 15 h, or 1 mg/L 1-MCP (1-methylcyclopropene) for 15 h, or 1 mg/L 1-MCP for 15 h + 500 mg/L ethylene for further 15 h, or air (control). All treatments were imposed at 20oC and 95–100% relative humidity. Samples undergoing treatment were then held in air at 20oC and 85% relative humidity for 13 days. Ethylene production from ethylene-treated grapes was very high (25 μL/kg.h) immediately after treatment, and declined progressively until day 6; 1-MCP-ethylene-treated grapes showed lower ethylene production (10 μL/kg.h). This high ethylene production was mainly due to in-out diffusion of ethylene absorbed during the treatment, but a potential effect of 1-MCP is postulated, since 1-MCP-treated grapes did not show ethylene production for 2 days after treatment, whereas control grapes produced constant amounts (3–4 μL/kg.h) of ethylene. After day 6, no significant difference was observed among samples. No difference in respiration was revealed. Total phenols were increased significantly by ethylene treatment from 520 mg/L up to 710, while total anthocyanins were lost in air-treated samples (from 175 mg/L to 120) and remained constant in ethylene and 1-MCP-treated grapes. HPLC analyses of anthocyanins confirmed this result: air-treated samples lost anthocyanins rapidly while this loss was delayed in gas-treated samples. Terpenols, esters, alcohols, and C6 compounds were increased by ethylene treatment. Conversely, 1-MCP-treated grapes showed a significant loss of terpenols and esters, although maintaining alcohols, especially hexan-1-ol. Berry pathology was also affected, with 1-MCP and 1-MCP-ethylene treated grapes hosting a diffuse attack of grey mould. Wine analyses revealed higher concentrations of phenols and anthocyanins in wine from ethylene-treated grapes, although aromatic compounds were lost, and thus the aroma profile of those wines was diminished.