applied sciences  
The Effect of Methyl Jasmonate-Doped Nano-Particles and Methyl Jasmonate on the Phenolics and Quality in Monastrell Grapes during the Ripening Period  
[PERSON] 1,*, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 2, [PERSON] 2 and [PERSON] 2  
the special characteristics in the different grape varieties and of the resulting wine. The concentration of polyphenols in grape berries depends on the grapevine variety and is influenced by viticultural and environmental factors [4, 5], and they are the most common chemical compounds present in grapes. Climate plays an important role in optimal grape growth and quality wine production [6, 7]. The increase in temperature, as a consequence of climate change, has resulted in advanced harvest dates in most of the wine producing countries [8]. In our area, southeast Spain, the climate is very warm and dry. Therefore, the current situation has resulted in an uncoupling of technological and phenolic maturity in red grape cultivars, resulting in unbalanced grape maturity and berry composition [9]. Different alternatives are being adopted in different world regions to mitigate the effects of climate change. This effect is noticeable in crops such as wine grapes (_Vitis vinifera_ L.), a very important crop in many places, which covers more than 7.4 million hectares worldwide with high social and economic impact [10]. In recent years, phytochemical contents and other quality parameters have been improved with pre- and post-harvest plant growth regulator treatments [11, 12]. Methyl jasmonate (MeJA) is among the most common of such plant growth regulators. It is an organic volatile compound derived from jasmonic acid that is present in several plant tissues. Its biological behaviour in plants is that it triggers the activity of the enzymes responsible for the biosynthesis of polyphenols, such as phenylalanine ammonia-lyap (PAL), polyphenol oxidase (PPO), peroxididases (POD) and other related enzymes [13, 14, 15, 16]. Since it has a regulatory role in fruit growth and ripening, it can easily affect the ripening processes of both climacter and non-climacter fruits [17, 18]. Different authors have studied MeJA's effect on grapes at harvest and its wines by investigating its effect on different families of analytes, such as phenolic and nitrogen compounds [19, 20]. Specifically, in wine grapes, several reports have shown that MeJA treatments on vineyards led to increased phenolic content, mainly anthocyanins, flavonoids and stilbenes, in grapes and wine, although huge differences between growing seasons and varieties were found [21, 22, 23, 24]. Nevertheless, no information is available in these papers regarding the effects of MeJA treatments on the grape ripening process. Only in a recent paper has a 10-day delay on the technological maturity ('Brix and pH), as a consequence of MeJA vineyard treatment, been reported in the wine variety 'Sangiovese' [25]. [PERSON] et al. [26] studied the evolution of phenolic compounds during ripening in grapes treated with MeJA and benzothiadiazole (BTH) in three different varieties (Monastrell, Syrah and Merlot). However, in all the mentioned works, to achieve an increase in the phenolic composition of grapes, it was necessary to use high concentrations of MeJA (10 mM). This concentration is the minimum to use in order to corroborate its effect, since other authors, such as [PERSON] et al. [27], have showed how the application of MeJA in two concentrations (5 mM and 10 mM) on Monastrell grapes in veraison only increased stilbene content when the higher concentration was applied (10 mM). In addition, a novel nanocomposite (i.e., Nano-MeJA) with amorphous structure (ACP), allowed to reduce the MeJA dosage to 1 mM while maintaining a stilbene content similar to the values obtained for MeJA at 10 mM [27].