Quality and Enhancement of Bioactive Phenolics in Cv. Napoleon Table Grapes Exposed to Different Postharvest Gaseous Treatments

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Abstract
Ten different gaseous treatments were evaluated for their efficacy in the keeping quality of cv. Napoleon table grapes during 38 days of storage at 0 °C followed by 6 days of shelf life at 15 °C in air. These storage methods included modified atmosphere packaging (MAP) with and without SO2 or natural fungicides (hexanal and hexenal), two controlled atmospheres (CA), and intermittent and continuous applications of O3. As a control, air atmosphere during cold storage was used. Most of the treatments applied kept the postharvest quality of the grapes, although the best results were obtained by the use of a MAP with 5 kPa of O2 plus 15 kPa of CO2 plus 80 kPa of N2. The total anthocyanin content at harvest was 170 ± 19 μg/g of fresh weight (fw) of grapes, which declined in most of the treatments applied and was reflected in the loss of red color. Peonidin 3-glucoside was detected at all sampling times as the major anthocyanin (always >50% from the total content). Treatments applied kept or decreased the total flavonol content from that measured at harvest (17 ± 1.4 μg/g of fw of berries). However, an increase of up to 2-fold in total stilbenoid content after shelf life for CA and O3 treatments was observed. At all sampling times for almost every treatment piceid concentration remained unaltered or slightly changed, whereas large increases were observed after shelf life for resveratrol (1.2 ± 0.6 μg/g of fw of grapes sampled at harvest), even up to 3- and 4-fold for O3-treated grapes and 2-fold for CA-treated ones. Therefore, improved techniques for the keeping quality of cv. Napoleon table grapes during long-term storage seem to maintain or enhance their antioxidant compound content. Keywords: Table grapes; modified atmosphere packaging; controlled atmosphere; ozone; sulfur dioxide; hexanal; hexenal; anthocyanins; flavonols; resveratrol; piceid; stilbenoids