## 3 Results
### Field Experiments on Vineyards  
#### 3.2.1 Evolution of Physicochemical Parameters in Grapes  
The evolution of the different physicochemical parameters studied (\({}^{\circ}\)Brix, total acidity, pH and berry weight) can be seen in Figure 2 (numerical data can be seen in ST1 of the Supplementary Materials). The results showed that physiological changes in the berries are evident after veraison, with a constant increase in sugar concentration, pH and weight of the berries, and a reduction in acidity. Other authors have observed the same results in grapes during grape maturation [36; 37]. Figure 1: TEM micrographs of Ap-MeJA (**A**) and Nano-MeJA (**B**) nanoparticles. Scale bar = 50 nm. Figure 2: Physicochemical parameters in grapes during ripening period (**(A)** evolution of \({}^{\circ}\)Brix; **(B)** evolution of total acidity; **(C)** evolution of pH and **(D)** evolution of berry weight). Abbreviations: MeJA: methyl jasmonate; Nano-MeJA: methyl jasmonate adsorbed on amorphous calcium phosphate; Ap-MeJA: methyl jasmonate adsorbed on nanocrystalline apatite. * Indicates significant differences among treatments according to [PERSON]’s test (\(p<0.05\)). With respect to the \({}^{\circ}\)Brix parameter, the evolution of the accumulation of sugars in the berries was faster in the control grapes than in the rest of the grapes treated with MeJA in its different forms. The sugar contents of the control samples, MeJA and Nano-MeJA, at different ripening stages ranged between 14.40 and 26.10, 25.56 and 25.35 \({}^{\circ}\)Brix, respectively, whereas in the case of Ap-MeJA it ranged between 14.40 and 24.80 \({}^{\circ}\)Brix. Thus, we were able to observe how from sampling 2, the \({}^{\circ}\)Brix was always higher in the control samples. On the other hand, it can be seen that up to the third sampling, the grapes treated with conventional MeJA are the ones that accumulate sugar more slowly, however from the fourth sampling, the grapes treated with nanoparticles accumulate sugar more slowly, highlighting the Ap-MeJA treatment. Only at harvest time were sugar concentrations equalised between control grapes and MeJA- and Nano-MeJA-treated grapes, and only Ap-MeJA-treated grapes were harvested with a lower \({}^{\circ}\)Brix. Therefore, it could be said that, in general, this treatment delayed the accumulation of sugars in the berries during the ripening period. Some studies showed a delay in the ripening process of grapes after applying MeJA, such as those by [PERSON] et al. [38] or [PERSON] et al. [24], where MeJA or Nano-MeJA were applied on Monastrell grapes, or in work by [PERSON] et al. [23], where this elicitor was applied in Graciano grapes. On the contrary, other authors have found an advance in the maturation of Tempranillo grapes [39]. It should be noted that a delay in the ripening process could be interesting in warm areas such as southeast Spain, where there is a decoupling between technological and phenolic maturity due to the consequences of climate change. As is normal, in Figure 2B, we can observe how acidity level decreased during the ripening period in the same way for control and treated grapes, finding no differences between Nano-MeJA and Ap-MeJA at the different ripening stages. The acidity values ranged between 15.13 and 2.45 and 2.25 and 2.40 g/L tartaric acid for Nano-MeJA and Ap-MeJA, respectively. We could observe how from the third sampling, the control grapes showed a more accelerated decrease in acidity compared to the treated grapes (see Table S1 of the Supplementary Materials). It can also be observed how in the fourth and fifth samplings, a somewhat less marked decrease was observed in the Nano-MeJA treatment (see Table S1 of the Supplementary Materials), although at harvest time all berries had very similar values. In contrast, other studies have shown an increase in total acidity at harvest time in Monastrell grapes [28; 40] or Tempranillo grapes when MeJA was applied [23].