*3.7. Microbiological Analysis*

Strawberry shows high metabolic activities and sensitivity against pathogens. The bioactive compounds and phytochemicals of the fruit rapidly decrease during storage [88]. Increased soluble sugars and sweetness and decreased acidity and defense metabolites, such as phenolic and antioxidants, make the fruit more susceptible to pathogen attack and postharvest losses [77].

The initial populations of total aerobic mesophilic bacteria and yeasts + molds in the fruit were 80 and 6 CFU g−1, respectively, which increased in the untreated and treated fruit during 16 days of cold storage (Figures 11 and 12), but the samples treated with *A. vera* gel alone or with lemongrass EO showed a strong effect on the total count of microbes in terms of preservation during the storage period, and the counts remained lower than in untreated fruits. These results are comparable with the results of coating with *A. vera* gel and cinnamon EO in modified atmosphere packaging of strawberry. A reduction in microbial populations during storage was observed but there was no change observed in the mold and yeast counts until day 10 of storage; however, on day 15, a decrease in the microbial load was noticed [89].

**Figure 11.** TMM (10<sup>3</sup> CFU.g−1) (mean <sup>±</sup> S.E.) of strawberry fruits stored at 5 ◦C as affected by coating treatments when store 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.

**Figure 12.** TYM (CFU g−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* gel. (**a**) First experiment; (**b**) second experiment.

At the end storage, the fruits treated with *A. vera* gel 40% and lemongrass EO recorded a lower microbial count than the fruits that underwent all other treatments. The control sample had the highest microbial count at the end of storage. Therefore, fruits treated with *A. vera* gel at 20% and 40% with lemongrass EO were able to resist fungal growth better than fruits treated with *A. vera* gel alone, and *A. vera* also remarkably reduced aerobic bacteria and yeast and mold counts during the 16 days of storage. In our study, a combination of *A. vera* gel and lemongrass EO seemed to have a synergistic effect on controlling microbial growth in strawberry during storage in a concentration-dependent manner. In a similar study, the effect of coating using *A. vera* gel 20% with 3% starch + 0.1% mandarin EO on physical and mechanical properties of blackberry indicated that this coating is suitable due to its thickness and shows the best mechanical properties observed, providing the fruit with greater thickness and improving its resistance to possible damage [90]. A bioactive coating combined with cinnamon EO significantly reduced mesophilic bacteria and yeast and molds in apple slices during a storage time of 25 days [91].

Coatings of *A. vera* gel with lemongrass EO effectively controlled or inhibited microbial populations (Figures 11 and 12). The present results are comparable with the results when sweet cherries and table grapes were coated with *A. vera* gel, which showed a reduction in the populations of mesophilic aerobic bacteria and yeast and mold during storage. *A. vera* gel compounds such as saponins, acemannan, and anthraquinones derivatives are reported to be responsible for antibacterial activity [92].

Rasouli et al. [93] reported that the inhibition effect of *A. vera* gel on microbial load arises from the presence of ingredients such as aleonin and aloeemodin, which is a possible rationale for the diminishing of germination and mycelial growth of fungi. Antara et al. [94] stated that the compounds responsible for the antimicrobial mechanism of lemongrass EO are a group of terpenoids, e.g., geranial (*β*-citral) and neral (*α*-citral).

Certain phenolic compounds are reported to be associated with antioxidant activity, such as radical-scavenging activity [95]. As shown in Figure 8, extracts contain polyphenols and flavonoids, which exhibit not only antioxidant activity but also antimicrobial activity (e.g., ferulic acid, caffeic acid, *p*-coumaric acid, syringic acid, sinapic acid, and cinnamic acid). Therefore, the antioxidant and antibacterial activities of extracts are linked to the activity of individual phenolic and flavonoid compounds. Extracts of *A. vera* gel 40% with lemongrass EO presented higher antimicrobial activity due to their high contents of total phenol content, total flavonoid content, and terpenoids. These results thus suggest that *A. vera* gel with lemongrass EO can be used as a natural antimicrobial.

Strawberries coated with *A. vera* gel 40% + lemongrass EO 1% had increased storage time because this treatment contributed to a decrease in the decay rate. Therefore, *A. vera* gel with lemongrass EO helps maintain the quality of strawberries during storage.

### **4. Conclusions**

The results obtained from this study show that an *Aloe vera* gel coating with lemongrass EO on strawberry fruit has a positive influence on the quality and biochemical properties of the fruit and reduces the microbial growth on the fruit. It was observed that between the two best treatments, treatment with *A. vera* gel 40% followed by *A. vera* gel 20% + lemongrass EO 1% gives better results as compared to treatment with *A. vera* gel (20% or 40%); additionally, for both treatments, significantly higher results were observed as compared to control. Treatment with *A. vera* gel 40% + lemongrass EO 1% enhanced the shelf life of the fruit at 5 ◦C by maintaining its quality and reducing the spoilage by postharvest pathogens. Thus, this treatment has the potential to be practiced on other different types of strawberry fruits. The present results may show an economical and natural way to improve fruit quality as well as resistance to a wide range of microorganisms.

**Author Contributions:** Conceptualization, H.S.H., M.E.-H. and D.Y.A.-E.; methodology, H.S.H., M.E.-H., M.S.R.A.E.-L., A.A.A.-H. and D.Y.A.-E.; software, H.S.H., M.S.R.A.E.-L., I.M.G., M.E.-H., A.A.A.-H., M.A. and D.Y.A.-E.; validation, H.S.H., M.E.-H., I.M.G., M.S.R.A.E.-L. and D.Y.A.-E.; formal analysis, H.S.H., M.E.-H. and D.Y.A.-E.; investigation, H.S.H., M.S.R.A.E.-L., I.M.G., M.E.-H., A.A.A.-H., M.A. and D.Y.A.-E.; resources, H.S.H., M.S.R.A.E.-L., I.M.G., M.E.-H., A.A.A.-H., M.A. and D.Y.A.-E.; data curation, H.S.H., M.S.R.A.E.-L., M.E.-H. and D.Y.A.-E.; writing—original draft preparation, H.S.H., M.S.R.A.E.-L., I.M.G., M.E.-H., H.M.A., M.A. and D.Y.A.-E.; writing—review and editing, H.S.H., M.S.R.A.E.-L., I.M.G., M.E.-H., A.A.A.-H., M.A. and D.Y.A.-E.; visualization, H.S.H., M.S.R.A.E.-L., I.M.G., M.E.-H., A.A.A.-H., M.A. and D.Y.A.-E.; supervision, H.S.H. and D.Y.A.-E.; project administration, D.Y.A.-E.; funding acquisition, A.A.A.-H. and H.M.A. Article revision, figure amendment, and proofreading of the revised article, H.S.H., M.E.-H., D.Y.A.-E. and H.M.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Researchers Supporting Project number (RSP-2021/186) King Saud University, Riyadh, Saudi Arabia.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Authors would like to extend their sincere appreciation to the Researchers Supporting Project number (RSP-2021/186), King Saud University, Riyadh, Saudi Arabia. Authors also acknowledge Alexandria University, Egypt for facilitating performing this research work as well.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

