Abstract
Abstract A comprehensive investigation was conducted to determine the effects of exogenous melatonin treatment of pre-veraison grapes on phenolic components and antioxidants of grape berries and wine. The results showed an increase in the concentration of cyanin-3-O-glucoside, peonidin derivatives, and two flavanols [namely (+)-catechins and (−)-epicatechins] of grapes, as well as flavonols in both grapes and wine due to the application of melatonin. These compounds are derivatives of the catalysate of flavonoid 3’-hydroxylase (F3’H) in the flavonoid synthesis pathway of plants. It can be inferred that melatonin increased the activity of F3’H or expression of VvF3’H during grape berry maturation. In addition, two melatonin treatments of pre-veraison grape berries reduced the DPPH radical-scavenging ability and copper ion-reducing power of grapes and wine, whereas one melatonin treatment just reduced those in wine. This study will provide a practical strategy to change the phenolic composition of grapes and wine.
Highlights
Phenolic compounds are some of the most important quality parameters of wine due to their direct influence on some important organoleptic characteristics (Garrido & Borges, 2011)
We investigated the effect of melatonin on the phenolic composition of mature grape berries and wine by spraying an exogenous melatonin solution on grape berries during the pre-veraison period
Melatonin treatment had increased the content of titratable acids, had no significant effect on Brix and total sugar
Summary
Phenolic compounds are some of the most important quality parameters of wine due to their direct influence on some important organoleptic characteristics (i.e. colour, flavour, bitterness, and astringency) (Garrido & Borges, 2011). The phenolics found in wine are active in biochemical processes and may offer significant antioxidant protection (Duthie et al, 2000). These translate to the fact that chemicals found in wine have the potential to overcome free radicals that are bound and determined to cause cellular damage, which are a root cause of various forms of cancer and cardiovascular diseases (Matés & Sánchez-Jiménez, 2000). The majority of phenolic compounds are grape-derived (Kennedy, 2008) Their composition and content in grape berries depends on the variety of the grapevine and is influenced by climatic and geographical factors, as well as cultural practices such as light, irrigation, temperature, soil, and plant growth regulators (Obreque-Slier et al, 2010). The use of plant growth regulators, including gibberellin, ethylene, cytokinins, abscisic acid, and salicylic acid is an effective method and is widely applied in grape cultivation
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