Using elicitors in different grape varieties. Effect over their phenolic composition

Abstract

Phenolic compounds are very important in crop plants and have been the subject of a large number of studies. Three main reasons can be cited for optimizing the level of phenolic compounds in crop plants: their physiological role in plants, their technological significance for food processing, and their nutritional characteristics1 Indeed, an enormous diversity of phenolic antioxidants is found in fruits and vegetables, and their presence and roles can be affected or modified by several pre- and postharvest cultural practices and/or food processing technologies (Ruiz-García et al. 2012, Goldman et al. 1999, Tudela et al. 2002). In winegrapes, the technological importance of phenolic compounds, mainly flavonoids, is well-known. They are responsible for the color of wines, especially anthocyanins (colored pigments responsible for the chromatic characteristics of red wines), tannins (responsible for the long-term stability of red wine color), and flavonols (compounds that may influence wine color through copigmentation). Moreover, they influence on other organoleptic properties such as astringency, bitterness, and body (Ruiz-García et al. 2012). Several techniques have been applied to improve the phenolic content of grapes. Leaving aside genetically modified plants, which are not allowed by the regulations of most countries, the most common techniques are related to cultural practices: pruning (González-Neves et al. 2002, Pérez-Lamela et al. 2007), cluster thinning (Fanzone et al. 2012, Soufleros et al. 2011), leaf removal (Gatti et al. 2012), and deficit irrigation (De la Hera et al. 2005, Koundouras et al. 2009). Another, more recent, technique for the same purpose is the use of elicitors, which are growing in interests. Elicitors are phytochemicals that do not kill pathogens themselves but trigger plant mechanisms that improve pathogen resistance, among them an increase in the levels of phenolic compounds (Vitallini et al. 2011), which are not only toxic to pathogens but also the precursors of disease-resistant material such as lignin (Pan and Liu 2011). This observed increase in phenolic compounds after the application of some elicitors justifies the interest in their application in fruits and vegetables. In our study, the effect of the application of benzhothiadiazol (BTH) and methyl jasmonate at veraison on the phenolic composition of grapes from three varieties (Monastrell, Cabernet Sauvignon and Merlot) was studied at harvest and after that, in wines at the end of alcoholic fermentation.The results showed that the effects of the treatments differed in the three varieties for the several phenolic compounds.