3.5.3. Total Anthocyanins

The change in the total anthocyanins of strawberry fruits coated with *A. vera* gel and *A. vera* gel with lemongrass EO is shown in Figure 7. The total anthocyanin content in all the treatments increased for the first 12 days of storage in both experiments. Thereafter, it decreased gradually for the remainder of storage. The untreated fruit showed the maximum anthocyanin concentration (277 mg·kg<sup>−</sup>1) on day 12 of the storage, followed by fruits treated with *A. vera* gel 40% + lemongrass EO 1% (246 mg·kg−1) and those treated with *A. vera* gel 20% + lemongrass EO 1% (221 mg·kg−1) at the end of the storage period, compared to 163 mg·kg−<sup>1</sup> when the fruits were initially stored.

**Figure 7.** Total anthocyanin (mg of cyanidin chloride.gm−1) (mean <sup>±</sup> S.E.) of strawberry fruits stored at 5 ◦C as affected by coating treatments when stored for different lengths of time in both experiments. The mean ± S.E. of treatments in the figures with the same letters shows a nonsignificant difference according to Duncan multiple range test for *p* ≤ 0.05. *A. vera* gel. (**a**) First experiment; (**b**) second experiment.

The significant increase in anthocyanin in control treatment could probably be related to the natural process during fruit ripening. However, the fruits treated with EOs showed a lower concentration of anthocyanin than the untreated ones. During cold storage the anthocyanin of treated fruits was increased, similar to those reported previously [77], which may be due to the continued biosynthesis of these compounds after harvest. Furthermore, total anthocyanin showed significant differences among fruits coated with a lemongrass EO and alginate-based edible coating [78].

### 3.5.4. Total Phenolic Content

It is clear from Figure 8 that all examined postharvest treatments decreased the total phenolic content (TPC) in both experiments. However, the highest TPC was recorded by untreated fruits, followed by fruits treated with *A. vera* gel 20%. The lowest values of TPC were scored by the treated fruits with *A. vera* gel 40% + lemongrass EO 1% and those treated with *A. vera* gel 20% + lemongrass EO 1% during both experiments. Figure 8 also indicates that regardless of the initial reading, the TPC was increased from day 4 to day 8 of storage.

**Figure 8.** Total phenolic content (mg of gallic acid.100 g fw−1) (mean <sup>±</sup> S.E.) of strawberry fruits stored at 5 ◦C as affected by coating treatments when stored for different lengths of time in both experiments. The mean ± S.E. of treatments in the figures with the same letters shows a nonsignificant difference according to Duncan multiple range test for *p* ≤ 0.05. AV: *A. vera*. (**a**) First experiment; (**b**) second experiment.

Anthocyanins are a group of phenolic compounds responsible for the red-blue color of many fruits and are important for human health [79]. The TPC and anthocyanin may be one of their most significant biological properties [80]. In the current study, the TPC decreased while anthocyanin increased in the untreated fruit. It is important for fruits to retain high levels of these compounds during storage and over their shelf life. The anthocyanin and TPC of the treated fruit increased during cold storage (Figure 8), similar to those reported previously [77], which may be due to the continued biosynthesis of these compounds after harvest. The evolution of the TPC of fruits during storage could be different depending on the species, temperature, cultivar, and climactic and environmental conditions during the growth period [48]. The findings indicate that both TPC and anthocyanin content in fruits treated with *A. vera* + ascorbic acid were higher than those in either untreated fruits or fruits treated with *A. vera* alone. Similarly, the use of ascorbic acid as a reducing agent prevented a decrease in the TPC in fresh-cut fruits [14,66].

### 3.5.5. Antioxidant Activity

The free-radical-scavenging activity (% inhibition) of strawberry fruits' ethanolic extracts was assessed by the DPPH test (Figure 9). Treatments with *A. vera* gel at 20% and 40% were more effective than treatment with *A. vera* gel with lemongrass EO, since the radical-scavenging activity was 77.04%, 74.58% and 58.22%, 54.29% for *A. vera* gel at 20% and 40% and *A. vera* gel with lemongrass EO, respectively, while it decreased in untreated extract to 64.24% at the end of the storage period. However, antioxidant activity was relatively stable during the 8 days of cold storage in fruits treated with *A. vera* gel and lemongrass EO, and the activity in fruits treated with *A. vera* gel at 20% or 40% was greater than the activity in fruits that underwent other treatments after 12 days of storage in both experiments. Moreover, the antioxidant activity decreased in untreated fruits and fruits treated with *A. vera* gel alone or combined with lemongrass EO. This means that *A. vera* gel at 20% and 40% has powerful potential antioxidant activity and increased the quality and stability of strawberry fruits.

**Figure 9.** Antioxidant activity (% capacity) (mean ± S.E.) of strawberry fruits stored at 5 ◦C as affected by coating treatments after being stored for different lengths of time in both experiments. The mean ± S.E. of treatments in the figures with the same letters shows a nonsignificant difference according to Duncan multiple range test for *p* ≤ 0.05. AV: *A. vera* gel. (**a**) First experiment; (**b**) second experiment.

Several studies have shown that strawberry is a good source of natural antioxidants [27]. It has been reported that fruits treated with *A. vera* had higher antioxidant capacity than the sample in the case of mango [81], raspberry [77], and table grapes (*Vitis vinifera* L. cv. Yaghouti) [82]. *A. vera* may also increase tissue resistance to decay by enhancing their antioxidant system and free-radical-scavenging capability [83]. Hidayati et al. [84] stated that antioxidant activity can be affected by the phenolic compounds and pigment content. Phenolic compounds and flavonoids as primary antioxidants can play an important role in absorbing and neutralizing free radicals, preventing the progress of diseases such as cancer [85].

### 3.5.6. Fruit Extraction and HPLC Analysis of the Fruit's Flavonoids

As presented in Table 6, the flavonoid concentration (μg/mL) of strawberry fruit was affected on treatment with *A. vera* gel and lemongrass EO. The highest value of rutin was obtained on treatment with *A. vera* gel 40% + lemongrass EO 1% compared with the initial value in the fruits and the value in the control fruit sample (16.25, 6.14, and 9.14 μg/mL, respectively). Naringin and hesperidin values were the best in the control, with concentrations of 8.16 and 14.56 μg/mL, respectively. Isorhamnetin and genistein were not detected in any treatment except for fruits treated with *A. vera* gel 40% + lemongrass EO 1%, with concentrations of 10.23 and 3.52 μg/mL, respectively. The highest concentration of quercetin was identified in strawberry fruits treated with *A. vera* gel 20% (15.36 μg/mL), the highest value of kaempferol was obtained on treatment with *A. vera* gel 40% (20.47 μg/mL), the highest values for luteolin and catechin were observed in fruits treated with *A. vera* gel 20% (14.66 and 20.56 μg/mL, respectively), and the highest value of 7-hydroxyflavone was obtained in fruits treated with *A. vera* gel 40% (14.16 μg/mL). The best value of chrysoeriol was observed in the initial sample, followed by fruits treated with *A. vera* gel 40%, with concentrations of 25.08 and 17.44 μg/mL. The compound myricetin was not detected in any treatment except in fruits treated with *A. vera* 40%, with a concentration of 2.25 μg/mL. These results are in good agreement with the studies of Hannum [86] and Co and Markakis [87].

**Table 6.** Flavonoid concentration in strawberry fruit as affected by different treatments of *A. vera* gel and lemongrass EO.


ND: not detected; R.T.: retention time.

### *3.6. EDX Analysis for Elemental Composition of Strawberry Fruits*

Table 7 and Figure 10 present the EDX analysis to measure the changes in the element composition of strawberry fruits due to different treatments. There was a significant effect of various treatments on element O percentage (*p* < 0.05), the highest value obtained on treatment with *A. vera* gel 20% (56.1%), followed by control (55.61%). There was a significant effect of treatments on element Ca percentage (*p* < 0.0001), with the highest value observed in strawberry fruits treated with *A. vera* gel 40% + lemongrass EO 1% (1.23%), followed by fruits treated with *A. vera* gel 20% + lemongrass EO 1% (0.48%). The rest of the treatments were not significant. However, the highest values of elements C, P, and K in strawberry fruits were obtained on treatment with *A. vera* gel 40% + lemongrass EO 1%, with percentages of 45.06%, 0.17%, and 1.8%, respectively, compared with the other treatments. The highest value of Mg in strawberry fruits was obtained on treatment with *A. vera* gel 40% (0.19%), whereas N was identified only in strawberry fruits treated with *A. vera* gel 40% alone.


**Table 7.** Elemental analysis of strawberry fruits coated by *A. vera* gel and lemongrass EO.

ns: not significant; the mean values with the same superscript letter/s within the same column show a nonsignificant difference according to LSD at 0.05 level of probability. nd: not detected.

**Figure 10.** EDX analysis for the elemental composition of strawberry fruits as affected by different treatments; each treatment was measured at three points.
