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

Alcatico grapes (Vitis vinifera L. cv. Aleatico) picked at 20.4-20.6 degrees Brix were treated with air containing 500 mg/L ethylene for 15 h, or I mg/L I-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 20 degrees C and 95-100% relative humidity. Samples undergoing treatment were then held in air at 20 degrees C and 85% relative humidity for 13 days. Ethylene production from ethylene-treated grapes was very high (25 mu L/kg.h) immediately after treatment, and declined progressively until day 6;1-MCP-ethylene-treated grapes showed lower ethylene production (10 mu L/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 mu L/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.