*3.3. Firmness*

Significant di fferences in firmness (*p* < 0.05) between the treatments were observed (Figure 1b) The firmness of the C group decreased from the beginning of the evaluation (6.33 ± 0.81 N to day 10), while the fruits covered with N25 and N50 showed the greatest firmness at day 30 (42.66 ± 4.88 and 39.66 ± 6.40 N, respectively), suggesting that the nanoemulsion is e ffective in maintaining firmness for longer compared to C.

#### *3.4. pH and Total Soluble Solids*

From Table 1 it is clear that significant di fferences in pH between treatments (*p* < 0.05) were found. At day 30, the C group showed a pH of 6.40 ± 0.03, and N25 had a pH of 6.15 ± 0.03, which was the most acid. The results for total soluble solids (Table 1) relate with the pH values, where C had higher total soluble solids than the rest of the treatments at day 30 (4.00 ± 0.01, 2.83 ± 0.05, 2.86 ± 0.05, and 3.23 ± 0.15 for C, CN, N50 and N25, respectively). These results are associated with the pH when indicating the lower acidity in the C group.


**Table 1.** Physicochemical changes in avocado during postharvest.

Different lowercase letters in the same row indicate significant differences (*p* < 0.05) between treatments at same analysis day. Different capital letters in the same column indicate significant differences (*p* < 0.05) between each treatment at different analysis day. Total soluble solids (TSS) are expressed in ◦Brix. Polyphenol oxidase (PPO) activity is expressed in increase in absorbance/0.1 mL of extract.

#### *3.5. Determination of Polyphenol Oxidase Activity*

PPO activity (Table 1) showed significant di fferences (*p* < 0.05) between the treatments. Greater activity in the C group at day 30 (0.29 ± 0.01) was observed, while N25 had the lowest PPO activity (0.21 ± 0.01), observing that the nanoemulsion is e ffective to keep inactive this enzyme causing the darkening of the mesocarp in fruits.

#### *3.6. Determination of Colour*

The external color of the avocado during ripening changed from green to black. In Table 2 the results of color are shown. No significant di fferences (*p* > 0.05) between the treatments were found in the L\* parameter, although there is a decrease in value over time. The results of parameter a\* (green color) displayed a significant decrease with all treatments after 30 days. The most significant e ffect was found in the controls (C), indicating a faster maturation which is associated with degradation of chlorophyll. The b\* parameter showed significant di fferences (*p* < 0.05) and decreased in the all treatments after 30 days.


**Table 2.** Color changes in the skin of the avocado during postharvest.

Different lowercase letters in the same row indicate significant differences (*p* < 0.05) between treatments at same analysis day. Different capital letters in the same column indicate significant differences (*p* < 0.05) between each treatment at different analysis day. L\* = lightness, a\* = green to red, b\* = blue to yellow.

Table 3 shows the color results in the mesocarp of avocado fruits. In parameter L\*, there are no significant differences (*p* > 0.05) between the treatments for each day of analysis, but a decrease in the brightness values respect to time is observed. Differences in the parameter a\* (*p* < 0.05) are observed for treatments at day 30. C showed a greater increase in values, which is associated with the loss of green color, behavior similar to that observed for parameter b \*, where C showed a loss of yellow color compared to the rest of the treatments at day 30.


**Table 3.** Color changes in the mesocarp of the avocado during postharvest.

Different lowercase letters in the same row indicate significant differences (*p* < 0.05) between treatments at same analysis day. Different capital letters in the same column indicate significant differences (*p* < 0.05) between each treatment at different analysis days. L\* = lightness, a\* = green to red, b\* = blue to yellow.

#### *3.7. Bioactive Compounds and Antioxidant Activity*

## 3.7.1. Total Phenols

The results demonstrate significant differences (*p* < 0.05) in total phenolic compounds in the avocado mesocarp over a 60-day period as well as between controls and treatments with nanoemulsions (Table 4). After 30 days, there was a substantial drop in total phenolic concentration for all the treatments, but afterwards, a significant increase followed until day 60. The highest concentrations of total phenols at day 60 were found with N25 and N50 treatments (214.29 ± 7.78 and 240.15 ± 16.29 mg EAG/100 g).


**Table 4.** Bioactive compounds and antioxidant activity changes in the mesocarp during postharvest.

Different lowercase letters in the same row indicate significant differences (*p* < 0.05) between treatments at same analysis day. The different capital letters in the same column indicate significant differences (*p* < 0.05) between each treatment at different analysis days. Total phenols are expressed in mg GAE/100 g, total flavonoids are expressed in mg QE/100 g, DPPH are expressed in mg AAE/100 g, and ABTS are expressed in mg AAE/100 g.

#### 3.7.2. Total Flavonoid Content

Table 4 shows an increase in the total flavonoid concentration with respect to time. At day 60, the highest concentration of flavonoids was observed in the N25 and N50 treatment groups (48.18 ± 1.78 and 47.77 ± 2.82 mg EQ/100 g, respectively).

#### 3.7.3. Determination of Antioxidant Activity

There were significant differences in the antioxidant activity when the DPPH radical was inhibited (*p* < 0.05) (Table 4). The treatments coated with the nanoemulsion presented an increase in antioxidant activity from day 30 to 60 that corresponded to the increase in bioactive compounds (phenols and flavonoids). The C treatment showed a different behavior, whereby there was a decrease in antioxidant activity with respect to time (Table 4). The results for the antioxidant activity in avocado mesocarp with the inhibition of the ABTS radical are shown in Table 4. These results are similar to those for the inhibition of the DPPH radical. Treatments coated with the nanoemulsion presented an increase in the antioxidant capacity from day 30 to day 60. The N25 treatment presented the best values of antioxidant activity at days 30 and 60 (211.40 ± 5.15 and 233.87 ± 5.94 mg EAA/100 g, respectively), while the C treatment presented the lowest values (112.48 ± 13.77 and 68.32 ± 5.42 mg EAA/100 g).

## *3.8. Structural Evaluation*

In Figure 2, the changes in the pericarp of the avocados with respect to time are shown, demonstrating that the exocarp is constructed by epidermal cells in a vertical disposition. In the immature fruit (day 0) a thick cuticle covering the epidermal tissue is clearly visible. One of the most prominent changes of the treatments up to day 30 was the lignification of the cell wall as accessed through the red staining protocol by the action of safranin.

**Figure 2.** Structural evaluation of the avocado epicarp with respect to time. The columns indicate the same treatment with respect to time and the rows indicate the same day of analysis for different treatments, c = cuticle, e = epidermis, p = parenchyma.
