**4. Discussion**

Postharvest weight loss is mainly attributed to perspiration caused by a deficit of steam pressure of the product in relation to its environment [22]. Sellamuthu et al. [23] found that weight loss decreased by applying thyme oil vapour and packaging of avocados from different cultivars in modified atmosphere and Russo et al. [24] observed that the firmness of the fruits decreased during storage from the fifth day in avocado fruits stored in different atmospheres (CO2/O2). Maftoonazad and Ramaswamy [15] applied a coating based on methylcellulose in avocado fruits, observing that coated treatments managed to maintain avocado firmness, which indicates that the use of a nanoemulsion as a coating is an effective alternative to prevent loss of firmness

Higher pH values can be associated with the conversion of organic acids and other complex molecules present in fruits into sugars, which is a source of energy reserve used in the metabolic processes during ripening [24,25]. Saucedo-Pompa et al. [26] coated avocado fruits with candelilla wax and ellagic acid and found that the fruits that were not coated had pH values closer to neutrality compared with the other treatments. Aguirre-Joya et al. [16] observed similar results in avocados coated with candelilla wax, pectin, aloe mucilage and polyphenols of *Larrea tridentate*, where the control showed a tendency to increase ◦Brix value as the storage time increased.

PPO is responsible for the darkening of the avocado, and it has been reported that PPO activity increases with a more accelerated ripening in stored fruits [23,27]. The results obtained in the present study are similar to those reported by Tesfay and Magwaza [2] in which the activity of PPO in the mesocarp of avocados decreased by applying edible moringa leaf extract coatings to avocado, showing that the maintenance of the integrity of the membrane in the coated fruit contributed to the reduction of darkening.

A decrease in luminosity in the epicarp of avocado has been related to the synthesis of some anthocyanins such as cyanidin 3-O-glucoside that confers dark colors [19]. The treatments that were coated with the nanoemulsion showed slower changes in colour, directly affecting the ripening attributes of the fruits [28]. Villa-Rodríguez et al. [19] evaluated the changes during the ripening of avocado fruits, reporting that there is a change in colour with respect to time that is related to the degradation (mainly chlorophyll) and synthesis of compounds. Correa-Pacheco et al. [29] determined

color in mesocarp and epicarp of avocado fruits coated with chitosan-thyme essential oil nanoparticles, observing that there were no differences between the coated and uncoated treatments; however, the results of the present study show that the nanoemulsion was able to maintain the color of the mesocarp as opposed to the fruits that were not coated. Cenobio-Galindo et al. [5] mentioned that bioactive compounds from xoconostle can remain effectively included in certain coatings without losing their activity, finding that certain compounds, such as rutin, ferulic acid, quercetin and apigenin, were maintained even after being incorporated into films and provided antioxidant activity.

Tesfay et al. [30] mentioned that the production of polyphenols can be stimulated by some biotic or abiotic factors; therefore, the application of the nanoemulsion could act as stimulus to increase phenolic compounds. Taking into account the results obtained, it is possible that this behavior is related to the diluted nanoemulsion treatments forming a more stable semipermeable coating with respect to the CN, and the stress in the fruit can remain for a longer time, affecting the synthesis of compounds. Wang et al. [20] evaluated the concentration of total phenols in different cultivars of avocado, finding that the cultivar "Hass" had high concentrations in the seeds and peels. Similar results were found by Vinha et al. [25], in which the concentration of total phenolics in avocados from the Algarve region in Portugal were highest in the seed and skin.

Sellamuthu et al. [23] indicated that essential oils can act as signaling compounds, causing a slight stress situation in the fruit, resulting in the increase in certain compounds, such as flavonoids. The procyanidins (catechin and epicatechin) are the main flavonoids present in avocados and are considered potent antioxidants with beneficial health effects [19,20]. From the results of Vinha et al. [25], it was clear that the highest concentration of total flavonoids was detected in the pericarp and seeds. Their reported value in the mesocarp was lower at 21.9 ± 1.0 mg / 100 g than our findings, in which, even at day 0, a higher amount (37.07 ± 0.71 mg EQ/100 g) was noted.

The antioxidant activity present in the avocado is given by the bioactive compounds present in the fruit, which include phenolic compounds such as procyanidins, chlorophylls and carotenoids [15]. Wang et al. [20] determined the antioxidant activity in different cultivars of avocado by inhibiting the DPPH radical and found that the cultivar "Hass" had the greatest antioxidant activity. Villa-Rodríguez et al. [19] determined antioxidant activity in avocado with different extractions and found that lipophilic extracts showed a greater antioxidant activity than hydrophilic extracts, compared by the different methods analyzed. There are reports suggesting that essential oils acting as signaling compounds are also capable of increasing antioxidant activity; therefore, nanoemulsions can fulfil this function [31].

Higher lignification of the cell walls in fruits treated with C and CN, compared to the N25 and N50 treatments, is an indication of accelerated maturation of the fruit. The colour change among treatments is because the green colour prevails in cells that have a slower metabolism, and cells that showed a more lignified wall were stained red by the action of safranin [32]. The effects that retard the fruit maturation (weight loss, firmness and PPO activity) are attributed to the action of the nanoemulsion as a coating. In all the treatments, it was observed that the cuticle remained until the end of the analysis. Schroeder [33] mentioned that the elimination or destruction of this protective epidermal layer makes the surface of the fruit more susceptible to attack by fungal and bacterial infections or can cause physiological disorders as a result of drying out.
