*Article* **Assessing the Use of** *Aloe vera* **Gel Alone and in Combination with Lemongrass Essential Oil as a Coating Material for Strawberry Fruits: HPLC and EDX Analyses**

**Hanaa S. Hassan 1, Mervat EL-Hefny 2,\*, Ibrahim M. Ghoneim 1, Mina S. R. Abd El-Lahot 3, Mohammad Akrami 4, Asma A. Al-Huqail 5, Hayssam M. Ali <sup>5</sup> and Doaa Y. Abd-Elkader <sup>1</sup>**


**Abstract:** Strawberry is a non-climacteric fruit but exhibits a limited postharvest life due to rapid softening and decay. A strawberry coating that is natural and safe for human consumption can be used to improve the appearance and safeguard the fruits. In this study, 20% and 40% *Aloe vera* gel alone or in combination with 1% lemongrass essential oil (EO) was used as an edible coating for strawberries. After application of all the treatments, the strawberry fruits were stored at a temperature of 5 ± 1 ◦C at a relative humidity (RH) of 90%–95% for up to 16 days and all the parameters were analyzed and compared to control (uncoated fruits). The results show that *A. vera* gel alone or with lemongrass EO reduced the deterioration and increased the shelf life of the fruit. Treatment with *A. vera* gel and lemongrass EO decreased acidity and total anthocyanins and maintained fruit firmness. Treatment with *A. vera* gel 40% + lemongrass EO 1% led to the lowest weight loss, retained firmness and acidity, but increased the total soluble solids and total anthocyanins compared to uncoated fruits during storage of up to 16 days. The phenolic compounds of *A. vera* gel were analyzed by HPLC, and the most abundant compounds were found to be caffeic (30.77 mg/mL), coumaric (22.4 mg/mL), syringic (15.12 mg/mL), sinapic (14.05 mg/mL), ferulic (8.22 mg/mL), and cinnamic acids (7.14 mg/mL). Lemongrass EO was analyzed by GC–MS, and the most abundant compounds were identified as *α*-citral (neral) (40.10%) *β*-citral (geranial) (30.71%), *γ*-dodecalactone (10.24%), isoneral (6.67%), neryl acetal (5.64%), and linalool (1.77%). When the fruits were treated with 20% or 40% *A. vera* gel along with 1% lemongrass, their total phenolic content was maintained during the storage period (from 4 to 8 days). The antioxidant activity was relatively stable during the 8 days of cold storage of the fruits coated with *A. vera* gel combined with lemongrass EO because the activity of both 20% and 40% gel was greater than that for the other treatments after 12 days of storage in both experiments. Moreover, all the treatments resulted in lower numbers of total microbes at the end of the storage period compared with the control treatment. This study indicates that the use of *Aloe vera* gel with lemongrass EO as an edible coating considerably enhances the productivity of strawberry fruits and the treatment could be used on a commercial scale.

**Keywords:** edible coatings; *Aloe vera* gel; lemongrass essential oil; shelf life; strawberry fruit

**Citation:** Hassan, H.S.; EL-Hefny, M.; Ghoneim, I.M.; El-Lahot, M.S.R.A.; Akrami, M.; Al-Huqail, A.A.; Ali, H.M.; Abd-Elkader, D.Y. Assessing the Use of *Aloe vera* Gel Alone and in Combination with Lemongrass Essential Oil as a Coating Material for Strawberry Fruits: HPLC and EDX Analyses. *Coatings* **2022**, *12*, 489. https://doi.org/10.3390/ coatings12040489

Academic Editor: Elena Torrieri

Received: 18 February 2022 Accepted: 1 April 2022 Published: 6 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

### **1. Introduction**

Strawberry (*Fragaria* × *ananassa*) is an economically important crop worldwide [1,2]. It has a great nutritional value because it contains minerals, vitamins, flavonoids, and phenolic compounds with beneficial biological properties, for instance antioxidant, anticancer, and anti-inflammatory activities [3,4]. Strawberry has tremendous prospects for commercial use, e.g., for the extraction of natural color with great potential for diverse value-added processed products [5]. However, the physiological characteristics of strawberry fruits deteriorate easily, as their softening reduces their postharvest shelf life during cold storage [6,7].

Postharvest losses in produce are a constant struggle for modern agriculture, which makes it urgent to develop new alternatives to reduce the waste [8,9]. To prolong the storage life of fresh and minimally processed fruits and vegetables, several physical, chemical, and biological alternatives and treatments have been proposed [10]. Recently, methods of ozone, electrolyzed water, modified/controlled atmospheric packaging, natural compounds, antifungal edible coatings, and biocontrol agents have emerged as safe alternatives and efficient preservation methods in the fresh produce industry [11–13].

Edible coatings are made up of natural polymers, such as carbohydrates, proteins, waxes, and their composites, that separate fruits from the surrounding atmosphere [14,15]. Coatings with edible films and essential oils (EOs) can also help to maintain the postharvest quality of fruits by reducing transpiration and respiration [16,17]. They also protect fruits and vegetables from deterioration by reducing the microbial growth and enhancing the textural quality [18–20].

*Aloe vera* (*Aloe barbadensis* Miller) is a succulent plant belonging to the family Asphodelaceae [21]. *A. vera* leaves have been used for many centuries for their therapeutic properties, and over 75 active ingredients have been identified in its gel [22].

*A. vera* gel is rich in soluble sugars and polysaccharides but has low properties of hydrophobic and lipid levels with gas barrier efficacy, making it an ideal edible coating material [23,24]. Moreover, *A. vera* gel coatings act as a barrier to moisture and O2, reducing the respiration rate, thereby preventing anaerobic conditions and conserving fruit quality [25].

As a coating material, *A. vera* gel maintains the texture, color, and shelf life of fruits and vegetables [26,27]. It is edible, invisible, odorless, and does not affect the quality of the fruit and vegetables, moreover, it is safe for human health and ecofriendly [28]. Furthermore, it reduces respiration rate, moisture loss, softening of tissues, oxidative browning, and proliferation of microorganisms in fruits, such as strawberry, cherry laurel fruit, and grapes [27,29,30]. Using *A. vera* gel dip coating reduced weight loss, changes in the physicochemical parameters, and decay, extending the shelf life of figs and litchi fruits [30,31].

EOs play an important role in the protection of the plants as they are antimicrobials and insecticides [32]. One of the advantages of plant EOs is their bioactivity in the vapor phase, which makes them possible fumigants to control postharvest rotting fungi in fruits and grains [33]. For example, lemongrass (*Cymbopogon citratus*), one of the important medicinal herbs, belonging to family Poaceae, is known to have strong antimicrobial and insecticidal properties [34–38]. It shows a strong fungicidal effect against microorganisms in fruit juices [39]. Lemongrass EOs are composed of terpenes and phenylpropenes compounds [40]. In addition, they contain other chemical groups like ketones, alcohols, esters, aldehyde, and flavonoid compounds [41]. The major components of Lemongrass EOs are nerol, *α*-citral, citronellal, *β*-citral, geraniol, terpinolene, myrcene, geranyl acetate, terpinol, and methylheptenone [34–37,42,43]. Mixtures of *A. vera* gel and EOs are widely studied as edible coatings for fresh-cut and whole fruit [14].

The present research assessed the effect of *A. vera* gel and lemongrass EO to enhance the postharvest quality, bioactive constituents, and shelf life of strawberry fruit.
