Evaluation of antibrowning and antioxidant activities in unripe grapes recovered during bunch thinning

Research into new systems for controlling enzymatic browning in the agro-food industry has been focused on eco-friendly alternatives to conventional thermal treatments and traditional additives, which could impair the sensory, nutritional and health properties. The use of unripe grapes for reducing alcohol concentration and pH of wines has been previously reported; however, no studies have been made of the evaluation of unripe grapes as potential functional ingredients to control enzymatic browning and to enhance antioxidant properties of plant products Therefore, unripe berries were collected in two seasons during bunch thinning of Barbera and Merlot vineyards. Merlot grapes,which had the highest antioxidant activity in the 2,2-diphenyl-1-picrylhydrazyl and ferric reducing ability of plasma assays,were also the most effective in preventing enzyme browning, as confirmed by spectrophotometric assays using commercial mushroom tyrosinase, by zymographic techniques on the isoforms isolated from some plant polyphenol oxidases and by in vivo trials on fresh-cut fruits and vegetables. In brief, the juice of unripe grapes showed not only antibrowning but also antioxidant and whitening activities. In addition, unripe grapes discarded during bunch thinning of vineyards represent for the agro-food industry a significant source of bioactive compounds that are easy to produce and safe for human health, thus converting these agricultural wastes into value-added products.