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

Abstract

Background and Aims: 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. Methods and Results: 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. Conclusions: The juice of unripe grapes showed not only antibrowning but also antioxidant and whitening activities. Significance: 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.

A Naturally Occurring Antioxidant Complex from Unripe Grapes: The Case of Sangiovese (v. Vitis vinifera)

“…A potential use of unripe grapes in winemaking to reduce the alcohol concentration and pH of wine was investigated by other authors, who observed a partial reduction of alcohol content and simultaneous decrease of pH of both Cabernet Sauvignon and Merlot experimental wines [ 12 ]. Although the bioactive compounds and antioxidant activities of grapes at maturity and by-products of the wine production chain have been the subject of many investigations, unripe grapes and their potential application in the food industry have been scarcely studied [ 13 , 14 ]. Unripe grapes are a source of natural antioxidants such as polyphenols and resveratrol.…”

Valorization of onion extracts as anti-browning agents

“…white, yellow, and red) were purchased from a local market, while the inner layers of Borettane onions were collected at the Naturello company (Pojana Maggiore, Vicenza, Italia). Juices and distillates were obtained from the peeled onions of white (CB and DB,), yellow (CG and DG) and red (CR and DR) varieties, and from Borettana onion wastes (CBo and DBo) by following the procedures described by Tinello and Lante (2017) and Lante and Tinello (2015), respectively. Onion samples were filtered through a Millipore 0.45μm filter membrane (Merck Millipore, Billerica, MA, USA) and stored at -20 °C in the dark until use.…”

“…The pH values were in the range of was approximately of 5.7±0.1 and 6.2±0.2 for onion juices and distillates, respectively. The inhibitory effect of onion juices and distillates as well as 0.05% w/v ascorbic acid (AA, reference inhibitor) on TYR and plant PPOs has been in vitro evaluated according to the spectrophotometric assay of Tinello and Lante (2017). Before measuring the enzyme activity, the freeze-dried enzymes were dissolved in 0.1 M sodium citrate buffer at pH 6.0 for TYR (9,390 U/mL), while at pH 6.0, 6.3, 5.5 for respectively potato (10 mg/mL), fennel (100 mg/mL) and eggplant (50 mg/mL) PPOs.…”

“…The images of zymograms were acquired by a scanner. The anti-browning effect was in vivo evaluated by monitoring over time (5, 10, 20, 30, 60 min) at 25 °C the colour change on the surface of potato slices treated with distilled water (C, control), onion samples and AA after 10 mM catechol application according to Tinello and Lante (2017).…”

“…Currently, the research of new anti-browning strategies is moving towards replacing synthetic additives (e.g. organic acids and sulphites) as well as thermal treatments with nonthermal technologies (Lante et al 2013;Lanteet al 2016) and/or natural extracts derived from plants (Zocca et al, 2011), agricultural by-products (Lante and Tinello 2015) and wastes (Zocca et al 2010;Tinello and Lante 2017;Tinello and Lante 2019). In this regard, the species belonging to the Allium family are recognized as a good source of healthy phenolic and organosulfur compounds (Corzo-Martínez et al 2007;Santas et al 2008;Mihaylova et al 2014;Putnik et al 2019).…”